| RFC : | rfc9605 |
| Title: | DNS Security Extensions (DNSSEC) |
| Date: | August 2024 |
| Status: | PROPOSED STANDARD |
Internet Engineering Task Force (IETF) E. Omara
Request for Comments: 9605 Apple
Category: Standards Track J. Uberti
ISSN: 2070-1721 Fixie.ai
S. G. Murillo
CoSMo Software
R. Barnes, Ed.
Cisco
Y. Fablet
Apple
August 2024
Secure Frame (SFrame): Lightweight Authenticated Encryption for
Real-Time Media
Abstract
This document describes the Secure Frame (SFrame) end-to-end
encryption and authentication mechanism for media frames in a
multiparty conference call, in which central media servers (Selective
Forwarding Units or SFUs) can access the media metadata needed to
make forwarding decisions without having access to the actual media.
This mechanism differs from the Secure Real-Time Protocol (SRTP) in
that it is independent of RTP (thus compatible with non-RTP media
transport) and can be applied to whole media frames in order to be
more bandwidth efficient.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9605.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
Table of Contents
1. Introduction
2. Terminology
3. Goals
4. SFrame
4.1. Application Context
4.2. SFrame Ciphertext
4.3. SFrame Header
4.4. Encryption Schema
4.4.1. Key Selection
4.4.2. Key Derivation
4.4.3. Encryption
4.4.4. Decryption
4.5. Cipher Suites
4.5.1. AES-CTR with SHA2
5. Key Management
5.1. Sender Keys
5.2. MLS
6. Media Considerations
6.1. Selective Forwarding Units
6.1.1. RTP Stream Reuse
6.1.2. Simulcast
6.1.3. Scalable Video Coding (SVC)
6.2. Video Key Frames
6.3. Partial Decoding
7. Security Considerations
7.1. No Header Confidentiality
7.2. No Per-Sender Authentication
7.3. Key Management
7.4. Replay
7.5. Risks Due to Short Tags
8. IANA Considerations
8.1. SFrame Cipher Suites
9. Application Responsibilities
9.1. Header Value Uniqueness
9.2. Key Management Framework
9.3. Anti-Replay
9.4. Metadata
10. References
10.1. Normative References
10.2. Informative References
Appendix A. Example API
Appendix B. Overhead Analysis
B.1. Assumptions
B.2. Audio
B.3. Video
B.4. Conferences
B.5. SFrame over RTP
Appendix C. Test Vectors
C.1. Header Encoding/Decoding
C.2. AEAD Encryption/Decryption Using AES-CTR and HMAC
C.3. SFrame Encryption/Decryption
Acknowledgements
Contributors
Authors' Addresses
1. Introduction
Modern multiparty video call systems use Selective Forwarding Unit
(SFU) servers to efficiently route media streams to call endpoints
based on factors such as available bandwidth, desired video size,
codec support, and other factors. An SFU typically does not need
access to the media content of the conference, which allows the media
to be encrypted "end to end" so that it cannot be decrypted by the
SFU. In order for the SFU to work properly, though, it usually needs
to be able to access RTP metadata and RTCP feedback messages, which
is not possible if all RTP/RTCP traffic is end-to-end encrypted.
As such, two layers of encryption and authentication are required:
1. Hop-by-hop (HBH) encryption of media, metadata, and feedback
messages between the endpoints and SFU
2. End-to-end (E2E) encryption (E2EE) of media between the endpoints
The Secure Real-Time Protocol (SRTP) is already widely used for HBH
encryption [RFC3711]. The SRTP "double encryption" scheme defines a
way to do E2E encryption in SRTP [RFC8723]. Unfortunately, this
scheme has poor efficiency and high complexity, and its entanglement
with RTP makes it unworkable in several realistic SFU scenarios.
This document proposes a new E2EE protection scheme known as SFrame,
specifically designed to work in group conference calls with SFUs.
SFrame is a general encryption framing that can be used to protect
media payloads, agnostic of transport.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
MAC: Message Authentication Code
E2EE: End-to-End Encryption
HBH: Hop-by-Hop
We use "Selective Forwarding Unit (SFU)" and "media stream" in a less
formal sense than in [RFC7656]. An SFU is a selective switching
function for media payloads, and a media stream is a sequence of
media payloads, regardless of whether those media payloads are
transported over RTP or some other protocol.
3. Goals
SFrame is designed to be a suitable E2EE protection scheme for
conference call media in a broad range of scenarios, as outlined by
the following goals:
1. Provide a secure E2EE mechanism for audio and video in conference
calls that can be used with arbitrary SFU servers.
2. Decouple media encryption from key management to allow SFrame to
be used with an arbitrary key management system.
3. Minimize packet expansion to allow successful conferencing in as
many network conditions as possible.
4. Decouple the media encryption framework from the underlying
transport, allowing use in non-RTP scenarios, e.g., WebTransport
[WEBTRANSPORT].
5. When used with RTP and its associated error-resilience
mechanisms, i.e., RTX and Forward Error Correction (FEC), require
no special handling for RTX and FEC packets.
6. Minimize the changes needed in SFU servers.
7. Minimize the changes needed in endpoints.
8. Work with the most popular audio and video codecs used in
conferencing scenarios.
4. SFrame
This document defines an encryption mechanism that provides effective
E2EE, is simple to implement, has no dependencies on RTP, and
minimizes encryption bandwidth overhead. This section describes how
the mechanism works and includes details of how applications utilize
SFrame for media protection as well as the actual mechanics of E2EE
for protecting media.
4.1. Application Context
SFrame is a general encryption framing, intended to be used as an
E2EE layer over an underlying HBH-encrypted transport such as SRTP or
QUIC [RFC3711][MOQ-TRANSPORT].
The scale at which SFrame encryption is applied to media determines
the overall amount of overhead that SFrame adds to the media stream
as well as the engineering complexity involved in integrating SFrame
into a particular environment. Two patterns are common: using SFrame
to encrypt either whole media frames (per frame) or individual
transport-level media payloads (per packet).
For example, Figure 1 shows a typical media sender stack that takes
media from some source, encodes it into frames, divides those frames
into media packets, and then sends those payloads in SRTP packets.
The receiver stack performs the reverse operations, reassembling
frames from SRTP packets and decoding. Arrows indicate two different
ways that SFrame protection could be integrated into this media
stack: to encrypt whole frames or individual media packets.
Applying SFrame per frame in this system offers higher efficiency but
may require a more complex integration in environments where
depacketization relies on the content of media packets. Applying
SFrame per packet avoids this complexity at the cost of higher
bandwidth consumption. Some quantitative discussion of these trade-
offs is provided in Appendix B.
As noted above, however, SFrame is a general media encapsulation and
can be applied in other scenarios. The important thing is that the
sender and receivers of an SFrame-encrypted object agree on that
object's semantics. SFrame does not provide this agreement; it must
be arranged by the application.
+------------------------------------------------------+
| |
| +--------+ +-------------+ +-----------+ |
.-. | | | | | | HBH | |
| | | | Encode |----->| Packetize |----->| Protect |----------+
'+' | | | ^ | | ^ | | | |
/|\ | +--------+ | +-------------+ | +-----------+ | |
/ + \ | | | ^ | |
/ \ | SFrame SFrame | | |
/ \ | Protect Protect | | |
Alice | (per frame) (per packet) | | |
| ^ ^ | | |
| | | | | |
+---------------|-------------------|---------|--------+ |
| | | v
| | | +------+-+
| E2E Key | HBH Key | Media |
+---- Management ---+ Management | Server |
| | | +------+-+
| | | |
+---------------|-------------------|---------|--------+ |
| | | | | |
| V V | | |
.-. | SFrame SFrame | | |
| | | Unprotect Unprotect | | |
'+' | (per frame) (per packet) | | |
/|\ | | | V | |
/ + \ | +--------+ | +-------------+ | +-----------+ | |
/ \ | | | V | | V | HBH | | |
/ \ | | Decode |<-----| Depacketize |<-----| Unprotect |<---------+
Bob | | | | | | | |
| +--------+ +-------------+ +-----------+ |
| |
+------------------------------------------------------+
Figure 1: Two Options for Integrating SFrame in a Typical Media Stack
Like SRTP, SFrame does not define how the keys used for SFrame are
exchanged by the parties in the conference. Keys for SFrame might be
distributed over an existing E2E-secure channel (see Section 5.1) or
derived from an E2E-secure shared secret (see Section 5.2). The key
management system MUST ensure that each key used for encrypting media
is used by exactly one media sender in order to avoid reuse of
nonces.
4.2. SFrame Ciphertext
An SFrame ciphertext comprises an SFrame header followed by the
output of an Authenticated Encryption with Associated Data (AEAD)
encryption of the plaintext [RFC5116], with the header provided as
additional authenticated data (AAD).
The SFrame header is a variable-length structure described in detail
in Section 4.3. The structure of the encrypted data and
authentication tag are determined by the AEAD algorithm in use.
+-+----+-+----+--------------------+--------------------+<-+
|K|KLEN|C|CLEN| Key ID | Counter | |
+->+-+----+-+----+--------------------+--------------------+ |
| | | |
| | | |
| | | |
| | | |
| | Encrypted Data | |
| | | |
| | | |
| | | |
| | | |
+->+-------------------------------------------------------+<-+
| | Authentication Tag | |
| +-------------------------------------------------------+ |
| |
| |
+--- Encrypted Portion Authenticated Portion ---+
Figure 2: Structure of an SFrame Ciphertext
When SFrame is applied per packet, the payload of each packet will be
an SFrame ciphertext. When SFrame is applied per frame, the SFrame
ciphertext representing an encrypted frame will span several packets,
with the header appearing in the first packet and the authentication
tag in the last packet. It is the responsibility of the application
to reassemble an encrypted frame from individual packets, accounting
for packet loss and reordering as necessary.
4.3. SFrame Header
The SFrame header specifies two values from which encryption
parameters are derived:
* A Key ID (KID) that determines which encryption key should be used
* A Counter (CTR) that is used to construct the nonce for the
encryption
Applications MUST ensure that each (KID, CTR) combination is used for
exactly one SFrame encryption operation. A typical approach to
achieve this guarantee is outlined in Section 9.1.
Config Byte
|
.-----' '-----.
| |
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+------------+------------+
|X| K |Y| C | KID... | CTR... |
+-+-+-+-+-+-+-+-+------------+------------+
Figure 3: SFrame Header
The SFrame header has the overall structure shown in Figure 3. The
first byte is a "config byte", with the following fields:
Extended KID Flag (X, 1 bit): Indicates if the K field contains the
KID or the KID length.
KID or KID Length (K, 3 bits): If the X flag is set to 0, this field
contains the KID. If the X flag is set to 1, then it contains the
length of the KID, minus one.
Extended CTR Flag (Y, 1 bit): Indicates if the C field contains the
CTR or the CTR length.
CTR or CTR Length (C, 3 bits): This field contains the CTR if the Y
flag is set to 0, or the CTR length, minus one, if set to 1.
The KID and CTR fields are encoded as compact unsigned integers in
network (big-endian) byte order. If the value of one of these fields
is in the range 0-7, then the value is carried in the corresponding
bits of the config byte (K or C) and the corresponding flag (X or Y)
is set to zero. Otherwise, the value MUST be encoded with the
minimum number of bytes required and appended after the config byte,
with the KID first and CTR second. The header field (K or C) is set
to the number of bytes in the encoded value, minus one. The value
000 represents a length of 1, 001 a length of 2, etc. This allows a
3-bit length field to represent the value lengths 1-8.
The SFrame header can thus take one of the four forms shown in
Figure 4, depending on which of the X and Y flags are set.
KID < 8, CTR < 8:
+-+-----+-+-----+
|0| KID |0| CTR |
+-+-----+-+-----+
KID < 8, CTR >= 8:
+-+-----+-+-----+------------------------+
|0| KID |1|CLEN | CTR... (length=CLEN) |
+-+-----+-+-----+------------------------+
KID >= 8, CTR < 8:
+-+-----+-+-----+------------------------+
|1|KLEN |0| CTR | KID... (length=KLEN) |
+-+-----+-+-----+------------------------+
KID >= 8, CTR >= 8:
+-+-----+-+-----+------------------------+------------------------+
|1|KLEN |1|CLEN | KID... (length=KLEN) | CTR... (length=CLEN) |
+-+-----+-+-----+------------------------+------------------------+
Figure 4: Forms of Encoded SFrame Header
4.4. Encryption Schema
SFrame encryption uses an AEAD encryption algorithm and hash function
defined by the cipher suite in use (see Section 4.5). We will refer
to the following aspects of the AEAD and the hash algorithm below:
* AEAD.Encrypt and AEAD.Decrypt - The encryption and decryption
functions for the AEAD. We follow the convention of RFC 5116
[RFC5116] and consider the authentication tag part of the
ciphertext produced by AEAD.Encrypt (as opposed to a separate
field as in SRTP [RFC3711]).
* AEAD.Nk - The size in bytes of a key for the encryption algorithm
* AEAD.Nn - The size in bytes of a nonce for the encryption
algorithm
* AEAD.Nt - The overhead in bytes of the encryption algorithm
(typically the size of a "tag" that is added to the plaintext)
* AEAD.Nka - For cipher suites using the compound AEAD described in
Section 4.5.1, the size in bytes of a key for the underlying
encryption algorithm
* Hash.Nh - The size in bytes of the output of the hash function
4.4.1. Key Selection
Each SFrame encryption or decryption operation is premised on a
single secret base_key, which is labeled with an integer KID value
signaled in the SFrame header.
The sender and receivers need to agree on which base_key should be
used for a given KID. Moreover, senders and receivers need to agree
on whether a base_key will be used for encryption or decryption only.
The process for provisioning base_key values and their KID values is
beyond the scope of this specification, but its security properties
will bound the assurances that SFrame provides. For example, if
SFrame is used to provide E2E security against intermediary media
nodes, then SFrame keys need to be negotiated in a way that does not
make them accessible to these intermediaries.
For each known KID value, the client stores the corresponding
symmetric key base_key. For keys that can be used for encryption,
the client also stores the next CTR value to be used when encrypting
(initially 0).
When encrypting a plaintext, the application specifies which KID is
to be used, and the CTR value is incremented after successful
encryption. When decrypting, the base_key for decryption is selected
from the available keys using the KID value in the SFrame header.
A given base_key MUST NOT be used for encryption by multiple senders.
Such reuse would result in multiple encrypted frames being generated
with the same (key, nonce) pair, which harms the protections provided
by many AEAD algorithms. Implementations MUST mark each base_key as
usable for encryption or decryption, never both.
Note that the set of available keys might change over the lifetime of
a real-time session. In such cases, the client will need to manage
key usage to avoid media loss due to a key being used to encrypt
before all receivers are able to use it to decrypt. For example, an
application may make decryption-only keys available immediately, but
delay the use of keys for encryption until (a) all receivers have
acknowledged receipt of the new key, or (b) a timeout expires.
4.4.2. Key Derivation
SFrame encryption and decryption use a key and salt derived from the
base_key associated with a KID. Given a base_key value, the key and
salt are derived using HMAC-based Key Derivation Function (HKDF)
[RFC5869] as follows:
def derive_key_salt(KID, base_key):
sframe_secret = HKDF-Extract("", base_key)
sframe_key_label = "SFrame 1.0 Secret key " + KID + cipher_suite
sframe_key =
HKDF-Expand(sframe_secret, sframe_key_label, AEAD.Nk)
sframe_salt_label = "SFrame 1.0 Secret salt " + KID + cipher_suite
sframe_salt =
HKDF-Expand(sframe_secret, sframe_salt_label, AEAD.Nn)
return sframe_key, sframe_salt
In the derivation of sframe_secret:
* The + operator represents concatenation of byte strings.
* The KID value is encoded as an 8-byte big-endian integer, not the
compressed form used in the SFrame header.
* The cipher_suite value is a 2-byte big-endian integer representing
the cipher suite in use (see Section 8.1).
The hash function used for HKDF is determined by the cipher suite in
use.
4.4.3. Encryption
SFrame encryption uses the AEAD encryption algorithm for the cipher
suite in use. The key for the encryption is the sframe_key. The
nonce is formed by first XORing the sframe_salt with the current CTR
value, and then encoding the result as a big-endian integer of length
AEAD.Nn.
The encryptor forms an SFrame header using the CTR and KID values
provided. The encoded header is provided as AAD to the AEAD
encryption operation, together with application-provided metadata
about the encrypted media (see Section 9.4).
def encrypt(CTR, KID, metadata, plaintext):
sframe_key, sframe_salt = key_store[KID]
# encode_big_endian(x, n) produces an n-byte string encoding the
# integer x in big-endian byte order.
ctr = encode_big_endian(CTR, AEAD.Nn)
nonce = xor(sframe_salt, CTR)
# encode_sframe_header produces a byte string encoding the
# provided KID and CTR values into an SFrame header.
header = encode_sframe_header(CTR, KID)
aad = header + metadata
ciphertext = AEAD.Encrypt(sframe_key, nonce, aad, plaintext)
return header + ciphertext
For example, the metadata input to encryption allows for frame
metadata to be authenticated when SFrame is applied per frame. After
encoding the frame and before packetizing it, the necessary media
metadata will be moved out of the encoded frame buffer to be sent in
some channel visible to the SFU (e.g., an RTP header extension).
+---------------+
| |
| |
| plaintext |
| |
| |
+-------+-------+
|
.- +-----+ |
| | +--+--> sframe_key ----->| Key
Header | | KID | | |
| | | +--> sframe_salt --+ |
+--+ +-----+ | |
| | | +---------------------+->| Nonce
| | | CTR | |
| | | | |
| '- +-----+ |
| |
| +----------------+ |
| | metadata | |
| +-------+--------+ |
| | |
+------------------+----------------->| AAD
| |
| AEAD.Encrypt
| |
| SFrame Ciphertext |
| +---------------+ |
+-------------->| SFrame Header | |
+---------------+ |
| | |
| |<----+
| ciphertext |
| |
| |
+---------------+
Figure 5: Encrypting an SFrame Ciphertext
4.4.4. Decryption
Before decrypting, a receiver needs to assemble a full SFrame
ciphertext. When an SFrame ciphertext is fragmented into multiple
parts for transport (e.g., a whole encrypted frame sent in multiple
SRTP packets), the receiving client collects all the fragments of the
ciphertext, using appropriate sequencing and start/end markers in the
transport. Once all of the required fragments are available, the
client reassembles them into the SFrame ciphertext and passes the
ciphertext to SFrame for decryption.
The KID field in the SFrame header is used to find the right key and
salt for the encrypted frame, and the CTR field is used to construct
the nonce. The SFrame decryption procedure is as follows:
def decrypt(metadata, sframe_ciphertext):
KID, CTR, header, ciphertext = parse_ciphertext(sframe_ciphertext)
sframe_key, sframe_salt = key_store[KID]
ctr = encode_big_endian(CTR, AEAD.Nn)
nonce = xor(sframe_salt, ctr)
aad = header + metadata
return AEAD.Decrypt(sframe_key, nonce, aad, ciphertext)
If a ciphertext fails to decrypt because there is no key available
for the KID in the SFrame header, the client MAY buffer the
ciphertext and retry decryption once a key with that KID is received.
If a ciphertext fails to decrypt for any other reason, the client
MUST discard the ciphertext. Invalid ciphertexts SHOULD be discarded
in a way that is indistinguishable (to an external observer) from
having processed a valid ciphertext. In other words, the SFrame
decrypt operation should take the same amount of time regardless of
whether decryption succeeds or fails.
SFrame Ciphertext
+---------------+
+---------------| SFrame Header |
| +---------------+
| | |
| | |-----+
| | ciphertext | |
| | | |
| | | |
| +---------------+ |
| |
| .- +-----+ |
| | | +--+--> sframe_key ----->| Key
| | | KID | | |
| | | | +--> sframe_salt --+ |
+->+ +-----+ | |
| | | +---------------------+->| Nonce
| | | CTR | |
| | | | |
| '- +-----+ |
| |
| +----------------+ |
| | metadata | |
| +-------+--------+ |
| | |
+------------------+----------------->| AAD
|
AEAD.Decrypt
|
V
+---------------+
| |
| |
| plaintext |
| |
| |
+---------------+
Figure 6: Decrypting an SFrame Ciphertext
4.5. Cipher Suites
Each SFrame session uses a single cipher suite that specifies the
following primitives:
* A hash function used for key derivation
* An AEAD encryption algorithm [RFC5116] used for frame encryption,
optionally with a truncated authentication tag
This document defines the following cipher suites, with the constants
defined in Section 4.4:
+============================+====+=====+====+====+====+
| Name | Nh | Nka | Nk | Nn | Nt |
+============================+====+=====+====+====+====+
| AES_128_CTR_HMAC_SHA256_80 | 32 | 16 | 48 | 12 | 10 |
+----------------------------+----+-----+----+----+----+
| AES_128_CTR_HMAC_SHA256_64 | 32 | 16 | 48 | 12 | 8 |
+----------------------------+----+-----+----+----+----+
| AES_128_CTR_HMAC_SHA256_32 | 32 | 16 | 48 | 12 | 4 |
+----------------------------+----+-----+----+----+----+
| AES_128_GCM_SHA256_128 | 32 | n/a | 16 | 12 | 16 |
+----------------------------+----+-----+----+----+----+
| AES_256_GCM_SHA512_128 | 64 | n/a | 32 | 12 | 16 |
+----------------------------+----+-----+----+----+----+
Table 1: SFrame Cipher Suite Constants
Numeric identifiers for these cipher suites are defined in the IANA
registry created in Section 8.1.
In the suite names, the length of the authentication tag is indicated
by the last value: "_128" indicates a 128-bit tag, "_80" indicates an
80-bit tag, "_64" indicates a 64-bit tag, and "_32" indicates a
32-bit tag.
In a session that uses multiple media streams, different cipher
suites might be configured for different media streams. For example,
in order to conserve bandwidth, a session might use a cipher suite
with 80-bit tags for video frames and another cipher suite with
32-bit tags for audio frames.
4.5.1. AES-CTR with SHA2
In order to allow very short tag sizes, we define a synthetic AEAD
function using the authenticated counter mode of AES together with
HMAC for authentication. We use an encrypt-then-MAC approach, as in
SRTP [RFC3711].
Before encryption or decryption, encryption and authentication
subkeys are derived from the single AEAD key. The overall length of
the AEAD key is Nka + Nh, where Nka represents the key size for the
AES block cipher in use and Nh represents the output size of the hash
function (as in Section 4.4). The encryption subkey comprises the
first Nka bytes and the authentication subkey comprises the remaining
Nh bytes.
def derive_subkeys(sframe_key):
# The encryption key comprises the first Nka bytes
enc_key = sframe_key[..Nka]
# The authentication key comprises Nh remaining bytes
auth_key = sframe_key[Nka..]
return enc_key, auth_key
The AEAD encryption and decryption functions are then composed of
individual calls to the CTR encrypt function and HMAC. The resulting
MAC value is truncated to a number of bytes Nt fixed by the cipher
suite.
def truncate(tag, n):
# Take the first `n` bytes of `tag`
return tag[..n]
def compute_tag(auth_key, nonce, aad, ct):
aad_len = encode_big_endian(len(aad), 8)
ct_len = encode_big_endian(len(ct), 8)
tag_len = encode_big_endian(Nt, 8)
auth_data = aad_len + ct_len + tag_len + nonce + aad + ct
tag = HMAC(auth_key, auth_data)
return truncate(tag, Nt)
def AEAD.Encrypt(key, nonce, aad, pt):
enc_key, auth_key = derive_subkeys(key)
initial_counter = nonce + 0x00000000 # append four zero bytes
ct = AES-CTR.Encrypt(enc_key, initial_counter, pt)
tag = compute_tag(auth_key, nonce, aad, ct)
return ct + tag
def AEAD.Decrypt(key, nonce, aad, ct):
inner_ct, tag = split_ct(ct, tag_len)
enc_key, auth_key = derive_subkeys(key)
candidate_tag = compute_tag(auth_key, nonce, aad, inner_ct)
if !constant_time_equal(tag, candidate_tag):
raise Exception("Authentication Failure")
initial_counter = nonce + 0x00000000 # append four zero bytes
return AES-CTR.Decrypt(enc_key, initial_counter, inner_ct)
5. Key Management
SFrame must be integrated with an E2E key management framework to
exchange and rotate the keys used for SFrame encryption. The key
management framework provides the following functions:
* Provisioning KID / base_key mappings to participating clients
* Updating the above data as clients join or leave
It is the responsibility of the application to provide the key
management framework, as described in Section 9.2.
5.1. Sender Keys
If the participants in a call have a preexisting E2E-secure channel,
they can use it to distribute SFrame keys. Each client participating
in a call generates a fresh base_key value that it will use to
encrypt media. The client then uses the E2E-secure channel to send
their encryption key to the other participants.
In this scheme, it is assumed that receivers have a signal outside of
SFrame for which client has sent a given frame (e.g., an RTP
synchronization source (SSRC)). SFrame KID values are then used to
distinguish between versions of the sender's base_key.
KID values in this scheme have two parts: a "key generation" and a
"ratchet step". Both are unsigned integers that begin at zero. The
key generation increments each time the sender distributes a new key
to receivers. The ratchet step is incremented each time the sender
ratchets their key forward for forward secrecy:
base_key[i+1] = HKDF-Expand(
HKDF-Extract("", base_key[i]),
"SFrame 1.0 Ratchet", CipherSuite.Nh)
For compactness, we do not send the whole ratchet step. Instead, we
send only its low-order R bits, where R is a value set by the
application. Different senders may use different values of R, but
each receiver of a given sender needs to know what value of R is used
by the sender so that they can recognize when they need to ratchet
(vs. expecting a new key). R effectively defines a reordering
window, since no more than 2^R ratchet steps can be active at a given
time. The key generation is sent in the remaining 64 - R bits of the
KID.
KID = (key_generation << R) + (ratchet_step % (1 << R))
64-R bits R bits
<---------------> <------------>
+-----------------+--------------+
| Key Generation | Ratchet Step |
+-----------------+--------------+
Figure 7: Structure of a KID in the Sender Keys Scheme
The sender signals such a ratchet step update by sending with a KID
value in which the ratchet step has been incremented. A receiver who
receives from a sender with a new KID computes the new key as above.
The old key may be kept for some time to allow for out-of-order
delivery, but should be deleted promptly.
If a new participant joins in the middle of a session, they will need
to receive from each sender (a) the current sender key for that
sender and (b) the current KID value for the sender. Evicting a
participant requires each sender to send a fresh sender key to all
receivers.
It is the application's responsibility to decide when sender keys are
updated. A sender key may be updated by sending a new base_key
(updating the key generation) or by hashing the current base_key
(updating the ratchet step). Ratcheting the key forward is useful
when adding new receivers to an SFrame-based interaction, since it
ensures that the new receivers can't decrypt any media encrypted
before they were added. If a sender wishes to assure the opposite
property when removing a receiver (i.e., ensuring that the receiver
can't decrypt media after they are removed), then the sender will
need to distribute a new sender key.
5.2. MLS
The Messaging Layer Security (MLS) protocol provides group
authenticated key exchange [MLS-ARCH] [MLS-PROTO]. In principle, it
could be used to instantiate the sender key scheme above, but it can
also be used more efficiently directly.
MLS creates a linear sequence of keys, each of which is shared among
the members of a group at a given point in time. When a member joins
or leaves the group, a new key is produced that is known only to the
augmented or reduced group. Each step in the lifetime of the group
is known as an "epoch", and each member of the group is assigned an
"index" that is constant for the time they are in the group.
To generate keys and nonces for SFrame, we use the MLS exporter
function to generate a base_key value for each MLS epoch. Each
member of the group is assigned a set of KID values so that each
member has a unique sframe_key and sframe_salt that it uses to
encrypt with. Senders may choose any KID value within their assigned
set of KID values, e.g., to allow a single sender to send multiple,
uncoordinated outbound media streams.
base_key = MLS-Exporter("SFrame 1.0 Base Key", "", AEAD.Nk)
For compactness, we do not send the whole epoch number. Instead, we
send only its low-order E bits, where E is a value set by the
application. E effectively defines a reordering window, since no
more than 2^E epochs can be active at a given time. To handle
rollover of the epoch counter, receivers MUST remove an old epoch
when a new epoch with the same low-order E bits is introduced.
Let S be the number of bits required to encode a member index in the
group, i.e., the smallest value such that group_size <= (1 << S).
The sender index is encoded in the S bits above the epoch. The
remaining 64 - S - E bits of the KID value are a context value chosen
by the sender (context value 0 will produce the shortest encoded
KID).
KID = (context << (S + E)) + (sender_index << E) + (epoch % (1 << E))
64-S-E bits S bits E bits
<-----------> <------> <------>
+-------------+--------+-------+
| Context ID | Index | Epoch |
+-------------+--------+-------+
Figure 8: Structure of a KID for an MLS Sender
Once an SFrame stack has been provisioned with the
sframe_epoch_secret for an epoch, it can compute the required KID
values on demand (as well as the resulting SFrame keys/nonces derived
from the base_key and KID) as it needs to encrypt or decrypt for a
given member.
...
|
|
Epoch 14 +--+-- index=3 ---> KID = 0x3e
| |
| +-- index=7 ---> KID = 0x7e
| |
| +-- index=20 --> KID = 0x14e
|
|
Epoch 15 +--+-- index=3 ---> KID = 0x3f
| |
| +-- index=5 ---> KID = 0x5f
|
|
Epoch 16 +----- index=2 --+--> context = 2 --> KID = 0x820
| |
| +--> context = 3 --> KID = 0xc20
|
|
Epoch 17 +--+-- index=33 --> KID = 0x211
| |
| +-- index=51 --> KID = 0x331
|
|
...
Figure 9: An Example Sequence of KIDs for an MLS-based SFrame
Session (E=4; S=6, Allowing for 64 Group Members)
6. Media Considerations
6.1. Selective Forwarding Units
SFUs (e.g., those described in Section 3.7 of [RFC7667]) receive the
media streams from each participant and select which ones should be
forwarded to each of the other participants. There are several
approaches for stream selection, but in general, the SFU needs to
access metadata associated with each frame and modify the RTP
information of the incoming packets when they are transmitted to the
received participants.
This section describes how these normal SFU modes of operation
interact with the E2EE provided by SFrame.
6.1.1. RTP Stream Reuse
The SFU may choose to send only a certain number of streams based on
the voice activity of the participants. To avoid the overhead
involved in establishing new transport streams, the SFU may decide to
reuse previously existing streams or even pre-allocate a predefined
number of streams and choose in each moment in time which participant
media will be sent through it.
This means that the same transport-level stream (e.g., an RTP stream
defined by either SSRC or Media Identification (MID)) may carry media
from different streams of different participants. Because each
participant uses a different key to encrypt their media, the receiver
will be able to verify the sender of the media within the RTP stream
at any given point in time. Thus the receiver will correctly
associate the media with the sender indicated by the authenticated
SFrame KID value, irrespective of how the SFU transmits the media to
the client.
Note that in order to prevent impersonation by a malicious
participant (not the SFU), a mechanism based on digital signature
would be required. SFrame does not protect against such attacks.
6.1.2. Simulcast
When using simulcast, the same input image will produce N different
encoded frames (one per simulcast layer), which would be processed
independently by the frame encryptor and assigned an unique CTR value
for each.
6.1.3. Scalable Video Coding (SVC)
In both temporal and spatial scalability, the SFU may choose to drop
layers in order to match a certain bitrate or to forward specific
media sizes or frames per second. In order to support the SFU
selectively removing layers, the sender MUST encapsulate each layer
in a different SFrame ciphertext.
6.2. Video Key Frames
Forward security and post-compromise security require that the E2EE
keys (base keys) are updated any time a participant joins or leaves
the call.
The key exchange happens asynchronously and on a different path than
the SFU signaling and media. So it may happen that when a new
participant joins the call and the SFU side requests a key frame, the
sender generates the E2EE frame with a key that is not known by the
receiver, so it will be discarded. When the sender updates his
sending key with the new key, it will send it in a non-key frame, so
the receiver will be able to decrypt it, but not decode it.
The new receiver will then re-request a key frame, but due to sender
and SFU policies, that new key frame could take some time to be
generated.
If the sender sends a key frame after the new E2EE key is in use, the
time required for the new participant to display the video is
minimized.
Note that this issue does not arise for media streams that do not
have dependencies among frames, e.g., audio streams. In these
streams, each frame is independently decodable, so a frame never
depends on another frame that might be on the other side of a key
rotation.
6.3. Partial Decoding
Some codecs support partial decoding, where individual packets can be
decoded without waiting for the full frame to arrive. When SFrame is
applied per frame, partial decoding is not possible because the
decoder cannot access data until an entire frame has arrived and has
been decrypted.
7. Security Considerations
7.1. No Header Confidentiality
SFrame provides integrity protection to the SFrame header (the KID
and CTR values), but it does not provide confidentiality protection.
Parties that can observe the SFrame header may learn, for example,
which parties are sending SFrame payloads (from KID values) and at
what rates (from CTR values). In cases where SFrame is used for end-
to-end security on top of hop-by-hop protections (e.g., running over
SRTP as described in Appendix B.5), the hop-by-hop security
mechanisms provide confidentiality protection of the SFrame header
between hops.
7.2. No Per-Sender Authentication
SFrame does not provide per-sender authentication of media data. Any
sender in a session can send media that will be associated with any
other sender. This is because SFrame uses symmetric encryption to
protect media data, so that any receiver also has the keys required
to encrypt packets for the sender.
7.3. Key Management
The specifics of key management are beyond the scope of this
document. However, every client SHOULD change their keys when new
clients join or leave the call for forward secrecy and post-
compromise security.
7.4. Replay
The handling of replay is out of the scope of this document.
However, senders MUST reject requests to encrypt multiple times with
the same key and nonce since several AEAD algorithms fail badly in
such cases (see, e.g., Section 5.1.1 of [RFC5116]).
7.5. Risks Due to Short Tags
The SFrame cipher suites based on AES-CTR allow for the use of short
authentication tags, which bring a higher risk that an attacker will
be able to cause an SFrame receiver to accept an SFrame ciphertext of
the attacker's choosing.
Assuming that the authentication properties of the cipher suite are
robust, the only attack that an attacker can mount is an attempt to
find an acceptable (ciphertext, tag) combination through brute force.
Such a brute-force attack will have an expected success rate of the
following form:
attacker_success_rate = attempts_per_second / 2^(8*Nt)
For example, a gigabit Ethernet connection is able to transmit
roughly 2^20 packets per second. If an attacker saturated such a
link with guesses against a 32-bit authentication tag (Nt=4), then
the attacker would succeed on average roughly once every 2^12
seconds, or about once an hour.
In a typical SFrame usage in a real-time media application, there are
a few approaches to mitigating this risk:
* Receivers only accept SFrame ciphertexts over HBH-secure channels
(e.g., SRTP security associations or QUIC connections). If this
is the case, only an entity that is part of such a channel can
mount the above attack.
* The expected packet rate for a media stream is very predictable
(and typically far lower than the above example). On the one
hand, attacks at this rate will succeed even less often than the
high-rate attack described above. On the other hand, the
application may use an elevated packet arrival rate as a signal of
a brute-force attack. This latter approach is common in other
settings, e.g., mitigating brute-force attacks on passwords.
* Media applications typically do not provide feedback to media
senders as to which media packets failed to decrypt. When media-
quality feedback mechanisms are used, decryption failures will
typically appear as packet losses, but only at an aggregate level.
* Anti-replay mechanisms (see Section 7.4) prevent the attacker from
reusing valid ciphertexts (either observed or guessed by the
attacker). A receiver applying anti-replay controls will only
accept one valid plaintext per CTR value. Since the CTR value is
covered by SFrame authentication, an attacker has to do a fresh
search for a valid tag for every forged ciphertext, even if the
encrypted content is unchanged. In other words, when the above
brute-force attack succeeds, it only allows the attacker to send a
single SFrame ciphertext; the ciphertext cannot be reused because
either it will have the same CTR value and be discarded as a
replay, or else it will have a different CTR value and its tag
will no longer be valid.
Nonetheless, without these mitigations, an application that makes use
of short tags will be at heightened risk of forgery attacks. In many
cases, it is simpler to use full-size tags and tolerate slightly
higher bandwidth usage rather than to add the additional defenses
necessary to safely use short tags.
8. IANA Considerations
IANA has created a new registry called "SFrame Cipher Suites"
(Section 8.1) under the "SFrame" group registry heading.
8.1. SFrame Cipher Suites
The "SFrame Cipher Suites" registry lists identifiers for SFrame
cipher suites as defined in Section 4.5. The cipher suite field is
two bytes wide, so the valid cipher suites are in the range 0x0000 to
0xFFFF. Except as noted below, assignments are made via the
Specification Required policy [RFC8126].
The registration template is as follows:
* Value: The numeric value of the cipher suite
* Name: The name of the cipher suite
* Recommended: Whether support for this cipher suite is recommended
by the IETF. Valid values are "Y", "N", and "D" as described in
Section 17.1 of [MLS-PROTO]. The default value of the
"Recommended" column is "N". Setting the Recommended item to "Y"
or "D", or changing an item whose current value is "Y" or "D",
requires Standards Action [RFC8126].
* Reference: The document where this cipher suite is defined
* Change Controller: Who is authorized to update the row in the
registry
Initial contents:
+========+============================+===+===========+============+
| Value | Name | R | Reference | Change |
| | | | | Controller |
+========+============================+===+===========+============+
| 0x0000 | Reserved | - | RFC 9605 | IETF |
+--------+----------------------------+---+-----------+------------+
| 0x0001 | AES_128_CTR_HMAC_SHA256_80 | Y | RFC 9605 | IETF |
+--------+----------------------------+---+-----------+------------+
| 0x0002 | AES_128_CTR_HMAC_SHA256_64 | Y | RFC 9605 | IETF |
+--------+----------------------------+---+-----------+------------+
| 0x0003 | AES_128_CTR_HMAC_SHA256_32 | Y | RFC 9605 | IETF |
+--------+----------------------------+---+-----------+------------+
| 0x0004 | AES_128_GCM_SHA256_128 | Y | RFC 9605 | IETF |
+--------+----------------------------+---+-----------+------------+
| 0x0005 | AES_256_GCM_SHA512_128 | Y | RFC 9605 | IETF |
+--------+----------------------------+---+-----------+------------+
| 0xF000 | Reserved for Private Use | - | RFC 9605 | IETF |
| - | | | | |
| 0xFFFF | | | | |
+--------+----------------------------+---+-----------+------------+
Table 2: SFrame Cipher Suites
9. Application Responsibilities
To use SFrame, an application needs to define the inputs to the
SFrame encryption and decryption operations, and how SFrame
ciphertexts are delivered from sender to receiver (including any
fragmentation and reassembly). In this section, we lay out
additional requirements that an application must meet in order for
SFrame to operate securely.
In general, an application using SFrame is responsible for
configuring SFrame. The application must first define when SFrame is
applied at all. When SFrame is applied, the application must define
which cipher suite is to be used. If new versions of SFrame are
defined in the future, it will be the application's responsibility to
determine which version should be used.
This division of responsibilities is similar to the way other media
parameters (e.g., codecs) are typically handled in media
applications, in the sense that they are set up in some signaling
protocol and not described in the media. Applications might find it
useful to extend the protocols used for negotiating other media
parameters (e.g., Session Description Protocol (SDP) [RFC8866]) to
also negotiate parameters for SFrame.
9.1. Header Value Uniqueness
Applications MUST ensure that each (base_key, KID, CTR) combination
is used for at most one SFrame encryption operation. This ensures
that the (key, nonce) pairs used by the underlying AEAD algorithm are
never reused. Typically this is done by assigning each sender a KID
or set of KIDs, then having each sender use the CTR field as a
monotonic counter, incrementing for each plaintext that is encrypted.
In addition to its simplicity, this scheme minimizes overhead by
keeping CTR values as small as possible.
In applications where an SFrame context might be written to
persistent storage, this context needs to include the last-used CTR
value. When the context is used later, the application should use
the stored CTR value to determine the next CTR value to be used in an
encryption operation, and then write the next CTR value back to
storage before using the CTR value for encryption. Storing the CTR
value before usage (vs. after) helps ensure that a storage failure
will not cause reuse of the same (base_key, KID, CTR) combination.
9.2. Key Management Framework
The application is responsible for provisioning SFrame with a mapping
of KID values to base_key values and the resulting keys and salts.
More importantly, the application specifies which KID values are used
for which purposes (e.g., by which senders). An application's KID
assignment strategy MUST be structured to assure the non-reuse
properties discussed in Section 9.1.
The application is also responsible for defining a rotation schedule
for keys. For example, one application might have an ephemeral group
for every call and keep rotating keys when endpoints join or leave
the call, while another application could have a persistent group
that can be used for multiple calls and simply derives ephemeral
symmetric keys for a specific call.
It should be noted that KID values are not encrypted by SFrame and
are thus visible to any application-layer intermediaries that might
handle an SFrame ciphertext. If there are application semantics
included in KID values, then this information would be exposed to
intermediaries. For example, in the scheme of Section 5.1, the
number of ratchet steps per sender is exposed, and in the scheme of
Section 5.2, the number of epochs and the MLS sender ID of the SFrame
sender are exposed.
9.3. Anti-Replay
It is the responsibility of the application to handle anti-replay.
Replay by network attackers is assumed to be prevented by network-
layer facilities (e.g., TLS, SRTP). As mentioned in Section 7.4,
senders MUST reject requests to encrypt multiple times with the same
key and nonce.
It is not mandatory to implement anti-replay on the receiver side.
Receivers MAY apply time- or counter-based anti-replay mitigations.
For example, Section 3.3.2 of [RFC3711] specifies a counter-based
anti-replay mitigation, which could be adapted to use with SFrame,
using the CTR field as the counter.
9.4. Metadata
The metadata input to SFrame operations is an opaque byte string
specified by the application. As such, the application needs to
define what information should go in the metadata input and ensure
that it is provided to the encryption and decryption functions at the
appropriate points. A receiver MUST NOT use SFrame-authenticated
metadata until after the SFrame decrypt function has authenticated
it, unless the purpose of such usage is to prepare an SFrame
ciphertext for SFrame decryption. Essentially, metadata may be used
"upstream of SFrame" in a processing pipeline, but only to prepare
for SFrame decryption.
For example, consider an application where SFrame is used to encrypt
audio frames that are sent over SRTP, with some application data
included in the RTP header extension. Suppose the application also
includes this application data in the SFrame metadata, so that the
SFU is allowed to read, but not modify, the application data. A
receiver can use the application data in the RTP header extension as
part of the standard SRTP decryption process since this is required
to recover the SFrame ciphertext carried in the SRTP payload.
However, the receiver MUST NOT use the application data for other
purposes before SFrame decryption has authenticated the application
data.
10. References
10.1. Normative References
[MLS-PROTO]
Barnes, R., Beurdouche, B., Robert, R., Millican, J.,
Omara, E., and K. Cohn-Gordon, "The Messaging Layer
Security (MLS) Protocol", RFC 9420, DOI 10.17487/RFC9420,
July 2023, <https://www.rfc-editor.org/info/rfc9420>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/info/rfc5869>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. Informative References
[MLS-ARCH] Beurdouche, B., Rescorla, E., Omara, E., Inguva, S., and
A. Duric, "The Messaging Layer Security (MLS)
Architecture", Work in Progress, Internet-Draft, draft-
ietf-mls-architecture-15, 3 August 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-mls-
architecture-15>.
[MOQ-TRANSPORT]
Curley, L., Pugin, K., Nandakumar, S., Vasiliev, V., and
I. Swett, Ed., "Media over QUIC Transport", Work in
Progress, Internet-Draft, draft-ietf-moq-transport-05, 8
July 2024, <https://datatracker.ietf.org/doc/html/draft-
ietf-moq-transport-05>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, DOI 10.17487/RFC3711, March 2004,
<https://www.rfc-editor.org/info/rfc3711>.
[RFC6716] Valin, JM., Vos, K., and T. Terriberry, "Definition of the
Opus Audio Codec", RFC 6716, DOI 10.17487/RFC6716,
September 2012, <https://www.rfc-editor.org/info/rfc6716>.
[RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and
B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms
for Real-Time Transport Protocol (RTP) Sources", RFC 7656,
DOI 10.17487/RFC7656, November 2015,
<https://www.rfc-editor.org/info/rfc7656>.
[RFC7667] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 7667,
DOI 10.17487/RFC7667, November 2015,
<https://www.rfc-editor.org/info/rfc7667>.
[RFC8723] Jennings, C., Jones, P., Barnes, R., and A.B. Roach,
"Double Encryption Procedures for the Secure Real-Time
Transport Protocol (SRTP)", RFC 8723,
DOI 10.17487/RFC8723, April 2020,
<https://www.rfc-editor.org/info/rfc8723>.
[RFC8866] Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP:
Session Description Protocol", RFC 8866,
DOI 10.17487/RFC8866, January 2021,
<https://www.rfc-editor.org/info/rfc8866>.
[RTP-PAYLOAD]
Murillo, S. G., Fablet, Y., and A. Gouaillard, "Codec
agnostic RTP payload format for video", Work in Progress,
Internet-Draft, draft-gouaillard-avtcore-codec-agn-rtp-
payload-01, 9 March 2021,
<https://datatracker.ietf.org/doc/html/draft-gouaillard-
avtcore-codec-agn-rtp-payload-01>.
[TestVectors]
"SFrame Test Vectors", commit 025d568, September 2023,
<https://github.com/sframe-wg/sframe/blob/025d568/test-
vectors/test-vectors.json>.
[WEBTRANSPORT]
Vasiliev, V., "The WebTransport Protocol Framework", Work
in Progress, Internet-Draft, draft-ietf-webtrans-overview-
08, 25 August 2024,
<https://datatracker.ietf.org/api/v1/doc/document/draft-
ietf-webtrans-overview/>.
Appendix A. Example API
*This section is not normative.*
This section describes a notional API that an SFrame implementation
might expose. The core concept is an "SFrame context", within which
KID values are meaningful. In the key management scheme described in
Section 5.1, each sender has a different context; in the scheme
described in Section 5.2, all senders share the same context.
An SFrame context stores mappings from KID values to "key contexts",
which are different depending on whether the KID is to be used for
sending or receiving (an SFrame key should never be used for both
operations). A key context tracks the key and salt associated to the
KID, and the current CTR value. A key context to be used for sending
also tracks the next CTR value to be used.
The primary operations on an SFrame context are as follows:
* *Create an SFrame context:* The context is initialized with a
cipher suite and no KID mappings.
* *Add a key for sending:* The key and salt are derived from the
base key and used to initialize a send context, together with a
zero CTR value.
* *Add a key for receiving:* The key and salt are derived from the
base key and used to initialize a send context.
* *Encrypt a plaintext:* Encrypt a given plaintext using the key for
a given KID, including the specified metadata.
* *Decrypt an SFrame ciphertext:* Decrypt an SFrame ciphertext with
the KID and CTR values specified in the SFrame header, and the
provided metadata.
Figure 10 shows an example of the types of structures and methods
that could be used to create an SFrame API in Rust.
type KeyId = u64;
type Counter = u64;
type CipherSuite = u16;
struct SendKeyContext {
key: Vec<u8>,
salt: Vec<u8>,
next_counter: Counter,
}
struct RecvKeyContext {
key: Vec<u8>,
salt: Vec<u8>,
}
struct SFrameContext {
cipher_suite: CipherSuite,
send_keys: HashMap<KeyId, SendKeyContext>,
recv_keys: HashMap<KeyId, RecvKeyContext>,
}
trait SFrameContextMethods {
fn create(cipher_suite: CipherSuite) -> Self;
fn add_send_key(&self, kid: KeyId, base_key: &[u8]);
fn add_recv_key(&self, kid: KeyId, base_key: &[u8]);
fn encrypt(&mut self, kid: KeyId, metadata: &[u8],
plaintext: &[u8]) -> Vec<u8>;
fn decrypt(&self, metadata: &[u8], ciphertext: &[u8]) -> Vec<u8>;
}
Figure 10: An Example SFrame API
Appendix B. Overhead Analysis
Any use of SFrame will impose overhead in terms of the amount of
bandwidth necessary to transmit a given media stream. Exactly how
much overhead will be added depends on several factors:
* The number of senders involved in a conference (length of KID)
* The duration of the conference (length of CTR)
* The cipher suite in use (length of authentication tag)
* Whether SFrame is used to encrypt packets, whole frames, or some
other unit
Overall, the overhead rate in kilobits per second can be estimated
as:
OverheadKbps = (1 + |CTR| + |KID| + |TAG|) * 8 * CTPerSecond / 1024
Here the constant value 1 reflects the fixed SFrame header; |CTR|
and |KID| reflect the lengths of those fields; |TAG| reflects the
cipher overhead; and CTPerSecond reflects the number of SFrame
ciphertexts sent per second (e.g., packets or frames per second).
In the remainder of this section, we compute overhead estimates for a
collection of common scenarios.
B.1. Assumptions
In the below calculations, we make conservative assumptions about
SFrame overhead so that the overhead amounts we compute here are
likely to be an upper bound of those seen in practice.
+==============+=======+============================+
| Field | Bytes | Explanation |
+==============+=======+============================+
| Config byte | 1 | Fixed |
+--------------+-------+----------------------------+
| Key ID (KID) | 2 | >255 senders; or MLS epoch |
| | | (E=4) and >16 senders |
+--------------+-------+----------------------------+
| Counter | 3 | More than 24 hours of |
| (CTR) | | media in common cases |
+--------------+-------+----------------------------+
| Cipher | 16 | Full authentication tag |
| overhead | | (longest defined here) |
+--------------+-------+----------------------------+
Table 3: Overhead Analysis Assumptions
In total, then, we assume that each SFrame encryption will add 22
bytes of overhead.
We consider two scenarios: applying SFrame per frame and per packet.
In each scenario, we compute the SFrame overhead in absolute terms
(kbps) and as a percentage of the base bandwidth.
B.2. Audio
In audio streams, there is typically a one-to-one relationship
between frames and packets, so the overhead is the same whether one
uses SFrame at a per-packet or per-frame level.
Table 4 considers three scenarios that are based on recommended
configurations of the Opus codec [RFC6716] (where "fps" stands for
"frames per second"):
+==============+==============+=====+======+==========+==========+
| Scenario | Frame length | fps | Base | Overhead | Overhead |
| | | | kbps | kbps | % |
+==============+==============+=====+======+==========+==========+
| Narrow-band | 120 ms | 8.3 | 8 | 1.4 | 17.9% |
| speech | | | | | |
+--------------+--------------+-----+------+----------+----------+
| Full-band | 20 ms | 50 | 32 | 8.6 | 26.9% |
| speech | | | | | |
+--------------+--------------+-----+------+----------+----------+
| Full-band | 10 ms | 100 | 128 | 17.2 | 13.4% |
| stereo music | | | | | |
+--------------+--------------+-----+------+----------+----------+
Table 4: SFrame Overhead for Audio Streams
B.3. Video
Video frames can be larger than an MTU and thus are commonly split
across multiple frames. Tables 5 and 6 show the estimated overhead
of encrypting a video stream, where SFrame is applied per frame and
per packet, respectively. The choices of resolution, frames per
second, and bandwidth roughly reflect the capabilities of modern
video codecs across a range from very low to very high quality.
+=============+=====+===========+===============+============+
| Scenario | fps | Base kbps | Overhead kbps | Overhead % |
+=============+=====+===========+===============+============+
| 426 x 240 | 7.5 | 45 | 1.3 | 2.9% |
+-------------+-----+-----------+---------------+------------+
| 640 x 360 | 15 | 200 | 2.6 | 1.3% |
+-------------+-----+-----------+---------------+------------+
| 640 x 360 | 30 | 400 | 5.2 | 1.3% |
+-------------+-----+-----------+---------------+------------+
| 1280 x 720 | 30 | 1500 | 5.2 | 0.3% |
+-------------+-----+-----------+---------------+------------+
| 1920 x 1080 | 60 | 7200 | 10.3 | 0.1% |
+-------------+-----+-----------+---------------+------------+
Table 5: SFrame Overhead for a Video Stream Encrypted per
Frame
+==========+=====+==============+======+==========+==========+
| Scenario | fps | Packets per | Base | Overhead | Overhead |
| | | Second (pps) | kbps | kbps | % |
+==========+=====+==============+======+==========+==========+
| 426 x | 7.5 | 7.5 | 45 | 1.3 | 2.9% |
| 240 | | | | | |
+----------+-----+--------------+------+----------+----------+
| 640 x | 15 | 30 | 200 | 5.2 | 2.6% |
| 360 | | | | | |
+----------+-----+--------------+------+----------+----------+
| 640 x | 30 | 60 | 400 | 10.3 | 2.6% |
| 360 | | | | | |
+----------+-----+--------------+------+----------+----------+
| 1280 x | 30 | 180 | 1500 | 30.9 | 2.1% |
| 720 | | | | | |
+----------+-----+--------------+------+----------+----------+
| 1920 x | 60 | 780 | 7200 | 134.1 | 1.9% |
| 1080 | | | | | |
+----------+-----+--------------+------+----------+----------+
Table 6: SFrame Overhead for a Video Stream Encrypted per
Packet
In the per-frame case, the SFrame percentage overhead approaches zero
as the quality of the video improves since bandwidth is driven more
by picture size than frame rate. In the per-packet case, the SFrame
percentage overhead approaches the ratio between the SFrame overhead
per packet and the MTU (here 22 bytes of SFrame overhead divided by
an assumed 1200-byte MTU, or about 1.8%).
B.4. Conferences
Real conferences usually involve several audio and video streams.
The overhead of SFrame in such a conference is the aggregate of the
overhead across all the individual streams. Thus, while SFrame
incurs a large percentage overhead on an audio stream, if the
conference also involves a video stream, then the audio overhead is
likely negligible relative to the overall bandwidth of the
conference.
For example, Table 7 shows the overhead estimates for a two-person
conference where one person is sending low-quality media and the
other is sending high-quality media. (And we assume that SFrame is
applied per frame.) The video streams dominate the bandwidth at the
SFU, so the total bandwidth overhead is only around 1%.
+=====================+===========+===============+============+
| Stream | Base Kbps | Overhead Kbps | Overhead % |
+=====================+===========+===============+============+
| Participant 1 audio | 8 | 1.4 | 17.9% |
+---------------------+-----------+---------------+------------+
| Participant 1 video | 45 | 1.3 | 2.9% |
+---------------------+-----------+---------------+------------+
| Participant 2 audio | 32 | 9 | 26.9% |
+---------------------+-----------+---------------+------------+
| Participant 2 video | 1500 | 5 | 0.3% |
+---------------------+-----------+---------------+------------+
| Total at SFU | 1585 | 16.5 | 1.0% |
+---------------------+-----------+---------------+------------+
Table 7: SFrame Overhead for a Two-Person Conference
B.5. SFrame over RTP
SFrame is a generic encapsulation format, but many of the
applications in which it is likely to be integrated are based on RTP.
This section discusses how an integration between SFrame and RTP
could be done, and some of the challenges that would need to be
overcome.
As discussed in Section 4.1, there are two natural patterns for
integrating SFrame into an application: applying SFrame per frame or
per packet. In RTP-based applications, applying SFrame per packet
means that the payload of each RTP packet will be an SFrame
ciphertext, starting with an SFrame header, as shown in Figure 11.
Applying SFrame per frame means that different RTP payloads will have
different formats: The first payload of a frame will contain the
SFrame headers, and subsequent payloads will contain further chunks
of the ciphertext, as shown in Figure 12.
In order for these media payloads to be properly interpreted by
receivers, receivers will need to be configured to know which of the
above schemes the sender has applied to a given sequence of RTP
packets. SFrame does not provide a mechanism for distributing this
configuration information. In applications that use SDP for
negotiating RTP media streams [RFC8866], an appropriate extension to
SDP could provide this function.
Applying SFrame per frame also requires that packetization and
depacketization be done in a generic manner that does not depend on
the media content of the packets, since the content being packetized
or depacketized will be opaque ciphertext (except for the SFrame
header). In order for such a generic packetization scheme to work
interoperably, one would have to be defined, e.g., as proposed in
[RTP-PAYLOAD].
+---+-+-+-------+-+-----------+------------------------------+<-+
|V=2|P|X| CC |M| PT | sequence number | |
+---+-+-+-------+-+-----------+------------------------------+ |
| timestamp | |
+------------------------------------------------------------+ |
| synchronization source (SSRC) identifier | |
+============================================================+ |
| contributing source (CSRC) identifiers | |
| .... | |
+------------------------------------------------------------+ |
| RTP extension(s) (OPTIONAL) | |
+->+-------------------+----------------------------------------+ |
| | SFrame header | | |
| +-------------------+ | |
| | | |
| | SFrame encrypted and authenticated payload | |
| | | |
+->+------------------------------------------------------------+<-+
| | SRTP authentication tag | |
| +------------------------------------------------------------+ |
| |
+--- SRTP Encrypted Portion SRTP Authenticated Portion ---+
Figure 11: SRTP Packet with SFrame-Protected Payload
+----------------+ +---------------+
| frame metadata | | |
+-------+--------+ | |
| | frame |
| | |
| | |
| +-------+-------+
| |
| |
V V
+--------------------------------------+
| SFrame Encrypt |
+--------------------------------------+
| |
| |
| V
| +-------+-------+
| | |
| | |
| | encrypted |
| | frame |
| | |
| | |
| +-------+-------+
| |
| generic RTP packetize
| |
| +----------------------+--------.....--------+
| | | |
V V V V
+---------------+ +---------------+ +---------------+
| SFrame header | | | | |
+---------------+ | | | |
| | | payload 2/N | ... | payload N/N |
| payload 1/N | | | | |
| | | | | |
+---------------+ +---------------+ +---------------+
Figure 12: Encryption Flow with per-Frame Encryption for RTP
Appendix C. Test Vectors
This section provides a set of test vectors that implementations can
use to verify that they correctly implement SFrame encryption and
decryption. In addition to test vectors for the overall process of
SFrame encryption/decryption, we also provide test vectors for header
encoding/decoding, and for AEAD encryption/decryption using the AES-
CTR construction defined in Section 4.5.1.
All values are either numeric or byte strings. Numeric values are
represented as hex values, prefixed with 0x. Byte strings are
represented in hex encoding.
Line breaks and whitespace within values are inserted to conform to
the width requirements of the RFC format. They should be removed
before use.
These test vectors are also available in JSON format at
[TestVectors]. In the JSON test vectors, numeric values are JSON
numbers and byte string values are JSON strings containing the hex
encoding of the byte strings.
C.1. Header Encoding/Decoding
For each case, we provide:
* kid: A KID value
* ctr: A CTR value
* header: An encoded SFrame header
An implementation should verify that:
* Encoding a header with the KID and CTR results in the provided
header value
* Decoding the provided header value results in the provided KID and
CTR values
kid: 0x0000000000000000
ctr: 0x0000000000000000
header: 00
kid: 0x0000000000000000
ctr: 0x0000000000000001
header: 01
kid: 0x0000000000000000
ctr: 0x00000000000000ff
header: 08ff
kid: 0x0000000000000000
ctr: 0x0000000000000100
header: 090100
kid: 0x0000000000000000
ctr: 0x000000000000ffff
header: 09ffff
kid: 0x0000000000000000
ctr: 0x0000000000010000
header: 0a010000
kid: 0x0000000000000000
ctr: 0x0000000000ffffff
header: 0affffff
kid: 0x0000000000000000
ctr: 0x0000000001000000
header: 0b01000000
kid: 0x0000000000000000
ctr: 0x00000000ffffffff
header: 0bffffffff
kid: 0x0000000000000000
ctr: 0x0000000100000000
header: 0c0100000000
kid: 0x0000000000000000
ctr: 0x000000ffffffffff
header: 0cffffffffff
kid: 0x0000000000000000
ctr: 0x0000010000000000
header: 0d010000000000
kid: 0x0000000000000000
ctr: 0x0000ffffffffffff
header: 0dffffffffffff
kid: 0x0000000000000000
ctr: 0x0001000000000000
header: 0e01000000000000
kid: 0x0000000000000000
ctr: 0x00ffffffffffffff
header: 0effffffffffffff
kid: 0x0000000000000000
ctr: 0x0100000000000000
header: 0f0100000000000000
kid: 0x0000000000000000
ctr: 0xffffffffffffffff
header: 0fffffffffffffffff
kid: 0x0000000000000001
ctr: 0x0000000000000000
header: 10
kid: 0x0000000000000001
ctr: 0x0000000000000001
header: 11
kid: 0x0000000000000001
ctr: 0x00000000000000ff
header: 18ff
kid: 0x0000000000000001
ctr: 0x0000000000000100
header: 190100
kid: 0x0000000000000001
ctr: 0x000000000000ffff
header: 19ffff
kid: 0x0000000000000001
ctr: 0x0000000000010000
header: 1a010000
kid: 0x0000000000000001
ctr: 0x0000000000ffffff
header: 1affffff
kid: 0x0000000000000001
ctr: 0x0000000001000000
header: 1b01000000
kid: 0x0000000000000001
ctr: 0x00000000ffffffff
header: 1bffffffff
kid: 0x0000000000000001
ctr: 0x0000000100000000
header: 1c0100000000
kid: 0x0000000000000001
ctr: 0x000000ffffffffff
header: 1cffffffffff
kid: 0x0000000000000001
ctr: 0x0000010000000000
header: 1d010000000000
kid: 0x0000000000000001
ctr: 0x0000ffffffffffff
header: 1dffffffffffff
kid: 0x0000000000000001
ctr: 0x0001000000000000
header: 1e01000000000000
kid: 0x0000000000000001
ctr: 0x00ffffffffffffff
header: 1effffffffffffff
kid: 0x0000000000000001
ctr: 0x0100000000000000
header: 1f0100000000000000
kid: 0x0000000000000001
ctr: 0xffffffffffffffff
header: 1fffffffffffffffff
kid: 0x00000000000000ff
ctr: 0x0000000000000000
header: 80ff
kid: 0x00000000000000ff
ctr: 0x0000000000000001
header: 81ff
kid: 0x00000000000000ff
ctr: 0x00000000000000ff
header: 88ffff
kid: 0x00000000000000ff
ctr: 0x0000000000000100
header: 89ff0100
kid: 0x00000000000000ff
ctr: 0x000000000000ffff
header: 89ffffff
kid: 0x00000000000000ff
ctr: 0x0000000000010000
header: 8aff010000
kid: 0x00000000000000ff
ctr: 0x0000000000ffffff
header: 8affffffff
kid: 0x00000000000000ff
ctr: 0x0000000001000000
header: 8bff01000000
kid: 0x00000000000000ff
ctr: 0x00000000ffffffff
header: 8bffffffffff
kid: 0x00000000000000ff
ctr: 0x0000000100000000
header: 8cff0100000000
kid: 0x00000000000000ff
ctr: 0x000000ffffffffff
header: 8cffffffffffff
kid: 0x00000000000000ff
ctr: 0x0000010000000000
header: 8dff010000000000
kid: 0x00000000000000ff
ctr: 0x0000ffffffffffff
header: 8dffffffffffffff
kid: 0x00000000000000ff
ctr: 0x0001000000000000
header: 8eff01000000000000
kid: 0x00000000000000ff
ctr: 0x00ffffffffffffff
header: 8effffffffffffffff
kid: 0x00000000000000ff
ctr: 0x0100000000000000
header: 8fff0100000000000000
kid: 0x00000000000000ff
ctr: 0xffffffffffffffff
header: 8fffffffffffffffffff
kid: 0x0000000000000100
ctr: 0x0000000000000000
header: 900100
kid: 0x0000000000000100
ctr: 0x0000000000000001
header: 910100
kid: 0x0000000000000100
ctr: 0x00000000000000ff
header: 980100ff
kid: 0x0000000000000100
ctr: 0x0000000000000100
header: 9901000100
kid: 0x0000000000000100
ctr: 0x000000000000ffff
header: 990100ffff
kid: 0x0000000000000100
ctr: 0x0000000000010000
header: 9a0100010000
kid: 0x0000000000000100
ctr: 0x0000000000ffffff
header: 9a0100ffffff
kid: 0x0000000000000100
ctr: 0x0000000001000000
header: 9b010001000000
kid: 0x0000000000000100
ctr: 0x00000000ffffffff
header: 9b0100ffffffff
kid: 0x0000000000000100
ctr: 0x0000000100000000
header: 9c01000100000000
kid: 0x0000000000000100
ctr: 0x000000ffffffffff
header: 9c0100ffffffffff
kid: 0x0000000000000100
ctr: 0x0000010000000000
header: 9d0100010000000000
kid: 0x0000000000000100
ctr: 0x0000ffffffffffff
header: 9d0100ffffffffffff
kid: 0x0000000000000100
ctr: 0x0001000000000000
header: 9e010001000000000000
kid: 0x0000000000000100
ctr: 0x00ffffffffffffff
header: 9e0100ffffffffffffff
kid: 0x0000000000000100
ctr: 0x0100000000000000
header: 9f01000100000000000000
kid: 0x0000000000000100
ctr: 0xffffffffffffffff
header: 9f0100ffffffffffffffff
kid: 0x000000000000ffff
ctr: 0x0000000000000000
header: 90ffff
kid: 0x000000000000ffff
ctr: 0x0000000000000001
header: 91ffff
kid: 0x000000000000ffff
ctr: 0x00000000000000ff
header: 98ffffff
kid: 0x000000000000ffff
ctr: 0x0000000000000100
header: 99ffff0100
kid: 0x000000000000ffff
ctr: 0x000000000000ffff
header: 99ffffffff
kid: 0x000000000000ffff
ctr: 0x0000000000010000
header: 9affff010000
kid: 0x000000000000ffff
ctr: 0x0000000000ffffff
header: 9affffffffff
kid: 0x000000000000ffff
ctr: 0x0000000001000000
header: 9bffff01000000
kid: 0x000000000000ffff
ctr: 0x00000000ffffffff
header: 9bffffffffffff
kid: 0x000000000000ffff
ctr: 0x0000000100000000
header: 9cffff0100000000
kid: 0x000000000000ffff
ctr: 0x000000ffffffffff
header: 9cffffffffffffff
kid: 0x000000000000ffff
ctr: 0x0000010000000000
header: 9dffff010000000000
kid: 0x000000000000ffff
ctr: 0x0000ffffffffffff
header: 9dffffffffffffffff
kid: 0x000000000000ffff
ctr: 0x0001000000000000
header: 9effff01000000000000
kid: 0x000000000000ffff
ctr: 0x00ffffffffffffff
header: 9effffffffffffffffff
kid: 0x000000000000ffff
ctr: 0x0100000000000000
header: 9fffff0100000000000000
kid: 0x000000000000ffff
ctr: 0xffffffffffffffff
header: 9fffffffffffffffffffff
kid: 0x0000000000010000
ctr: 0x0000000000000000
header: a0010000
kid: 0x0000000000010000
ctr: 0x0000000000000001
header: a1010000
kid: 0x0000000000010000
ctr: 0x00000000000000ff
header: a8010000ff
kid: 0x0000000000010000
ctr: 0x0000000000000100
header: a90100000100
kid: 0x0000000000010000
ctr: 0x000000000000ffff
header: a9010000ffff
kid: 0x0000000000010000
ctr: 0x0000000000010000
header: aa010000010000
kid: 0x0000000000010000
ctr: 0x0000000000ffffff
header: aa010000ffffff
kid: 0x0000000000010000
ctr: 0x0000000001000000
header: ab01000001000000
kid: 0x0000000000010000
ctr: 0x00000000ffffffff
header: ab010000ffffffff
kid: 0x0000000000010000
ctr: 0x0000000100000000
header: ac0100000100000000
kid: 0x0000000000010000
ctr: 0x000000ffffffffff
header: ac010000ffffffffff
kid: 0x0000000000010000
ctr: 0x0000010000000000
header: ad010000010000000000
kid: 0x0000000000010000
ctr: 0x0000ffffffffffff
header: ad010000ffffffffffff
kid: 0x0000000000010000
ctr: 0x0001000000000000
header: ae01000001000000000000
kid: 0x0000000000010000
ctr: 0x00ffffffffffffff
header: ae010000ffffffffffffff
kid: 0x0000000000010000
ctr: 0x0100000000000000
header: af0100000100000000000000
kid: 0x0000000000010000
ctr: 0xffffffffffffffff
header: af010000ffffffffffffffff
kid: 0x0000000000ffffff
ctr: 0x0000000000000000
header: a0ffffff
kid: 0x0000000000ffffff
ctr: 0x0000000000000001
header: a1ffffff
kid: 0x0000000000ffffff
ctr: 0x00000000000000ff
header: a8ffffffff
kid: 0x0000000000ffffff
ctr: 0x0000000000000100
header: a9ffffff0100
kid: 0x0000000000ffffff
ctr: 0x000000000000ffff
header: a9ffffffffff
kid: 0x0000000000ffffff
ctr: 0x0000000000010000
header: aaffffff010000
kid: 0x0000000000ffffff
ctr: 0x0000000000ffffff
header: aaffffffffffff
kid: 0x0000000000ffffff
ctr: 0x0000000001000000
header: abffffff01000000
kid: 0x0000000000ffffff
ctr: 0x00000000ffffffff
header: abffffffffffffff
kid: 0x0000000000ffffff
ctr: 0x0000000100000000
header: acffffff0100000000
kid: 0x0000000000ffffff
ctr: 0x000000ffffffffff
header: acffffffffffffffff
kid: 0x0000000000ffffff
ctr: 0x0000010000000000
header: adffffff010000000000
kid: 0x0000000000ffffff
ctr: 0x0000ffffffffffff
header: adffffffffffffffffff
kid: 0x0000000000ffffff
ctr: 0x0001000000000000
header: aeffffff01000000000000
kid: 0x0000000000ffffff
ctr: 0x00ffffffffffffff
header: aeffffffffffffffffffff
kid: 0x0000000000ffffff
ctr: 0x0100000000000000
header: afffffff0100000000000000
kid: 0x0000000000ffffff
ctr: 0xffffffffffffffff
header: afffffffffffffffffffffff
kid: 0x0000000001000000
ctr: 0x0000000000000000
header: b001000000
kid: 0x0000000001000000
ctr: 0x0000000000000001
header: b101000000
kid: 0x0000000001000000
ctr: 0x00000000000000ff
header: b801000000ff
kid: 0x0000000001000000
ctr: 0x0000000000000100
header: b9010000000100
kid: 0x0000000001000000
ctr: 0x000000000000ffff
header: b901000000ffff
kid: 0x0000000001000000
ctr: 0x0000000000010000
header: ba01000000010000
kid: 0x0000000001000000
ctr: 0x0000000000ffffff
header: ba01000000ffffff
kid: 0x0000000001000000
ctr: 0x0000000001000000
header: bb0100000001000000
kid: 0x0000000001000000
ctr: 0x00000000ffffffff
header: bb01000000ffffffff
kid: 0x0000000001000000
ctr: 0x0000000100000000
header: bc010000000100000000
kid: 0x0000000001000000
ctr: 0x000000ffffffffff
header: bc01000000ffffffffff
kid: 0x0000000001000000
ctr: 0x0000010000000000
header: bd01000000010000000000
kid: 0x0000000001000000
ctr: 0x0000ffffffffffff
header: bd01000000ffffffffffff
kid: 0x0000000001000000
ctr: 0x0001000000000000
header: be0100000001000000000000
kid: 0x0000000001000000
ctr: 0x00ffffffffffffff
header: be01000000ffffffffffffff
kid: 0x0000000001000000
ctr: 0x0100000000000000
header: bf010000000100000000000000
kid: 0x0000000001000000
ctr: 0xffffffffffffffff
header: bf01000000ffffffffffffffff
kid: 0x00000000ffffffff
ctr: 0x0000000000000000
header: b0ffffffff
kid: 0x00000000ffffffff
ctr: 0x0000000000000001
header: b1ffffffff
kid: 0x00000000ffffffff
ctr: 0x00000000000000ff
header: b8ffffffffff
kid: 0x00000000ffffffff
ctr: 0x0000000000000100
header: b9ffffffff0100
kid: 0x00000000ffffffff
ctr: 0x000000000000ffff
header: b9ffffffffffff
kid: 0x00000000ffffffff
ctr: 0x0000000000010000
header: baffffffff010000
kid: 0x00000000ffffffff
ctr: 0x0000000000ffffff
header: baffffffffffffff
kid: 0x00000000ffffffff
ctr: 0x0000000001000000
header: bbffffffff01000000
kid: 0x00000000ffffffff
ctr: 0x00000000ffffffff
header: bbffffffffffffffff
kid: 0x00000000ffffffff
ctr: 0x0000000100000000
header: bcffffffff0100000000
kid: 0x00000000ffffffff
ctr: 0x000000ffffffffff
header: bcffffffffffffffffff
kid: 0x00000000ffffffff
ctr: 0x0000010000000000
header: bdffffffff010000000000
kid: 0x00000000ffffffff
ctr: 0x0000ffffffffffff
header: bdffffffffffffffffffff
kid: 0x00000000ffffffff
ctr: 0x0001000000000000
header: beffffffff01000000000000
kid: 0x00000000ffffffff
ctr: 0x00ffffffffffffff
header: beffffffffffffffffffffff
kid: 0x00000000ffffffff
ctr: 0x0100000000000000
header: bfffffffff0100000000000000
kid: 0x00000000ffffffff
ctr: 0xffffffffffffffff
header: bfffffffffffffffffffffffff
kid: 0x0000000100000000
ctr: 0x0000000000000000
header: c00100000000
kid: 0x0000000100000000
ctr: 0x0000000000000001
header: c10100000000
kid: 0x0000000100000000
ctr: 0x00000000000000ff
header: c80100000000ff
kid: 0x0000000100000000
ctr: 0x0000000000000100
header: c901000000000100
kid: 0x0000000100000000
ctr: 0x000000000000ffff
header: c90100000000ffff
kid: 0x0000000100000000
ctr: 0x0000000000010000
header: ca0100000000010000
kid: 0x0000000100000000
ctr: 0x0000000000ffffff
header: ca0100000000ffffff
kid: 0x0000000100000000
ctr: 0x0000000001000000
header: cb010000000001000000
kid: 0x0000000100000000
ctr: 0x00000000ffffffff
header: cb0100000000ffffffff
kid: 0x0000000100000000
ctr: 0x0000000100000000
header: cc01000000000100000000
kid: 0x0000000100000000
ctr: 0x000000ffffffffff
header: cc0100000000ffffffffff
kid: 0x0000000100000000
ctr: 0x0000010000000000
header: cd0100000000010000000000
kid: 0x0000000100000000
ctr: 0x0000ffffffffffff
header: cd0100000000ffffffffffff
kid: 0x0000000100000000
ctr: 0x0001000000000000
header: ce010000000001000000000000
kid: 0x0000000100000000
ctr: 0x00ffffffffffffff
header: ce0100000000ffffffffffffff
kid: 0x0000000100000000
ctr: 0x0100000000000000
header: cf01000000000100000000000000
kid: 0x0000000100000000
ctr: 0xffffffffffffffff
header: cf0100000000ffffffffffffffff
kid: 0x000000ffffffffff
ctr: 0x0000000000000000
header: c0ffffffffff
kid: 0x000000ffffffffff
ctr: 0x0000000000000001
header: c1ffffffffff
kid: 0x000000ffffffffff
ctr: 0x00000000000000ff
header: c8ffffffffffff
kid: 0x000000ffffffffff
ctr: 0x0000000000000100
header: c9ffffffffff0100
kid: 0x000000ffffffffff
ctr: 0x000000000000ffff
header: c9ffffffffffffff
kid: 0x000000ffffffffff
ctr: 0x0000000000010000
header: caffffffffff010000
kid: 0x000000ffffffffff
ctr: 0x0000000000ffffff
header: caffffffffffffffff
kid: 0x000000ffffffffff
ctr: 0x0000000001000000
header: cbffffffffff01000000
kid: 0x000000ffffffffff
ctr: 0x00000000ffffffff
header: cbffffffffffffffffff
kid: 0x000000ffffffffff
ctr: 0x0000000100000000
header: ccffffffffff0100000000
kid: 0x000000ffffffffff
ctr: 0x000000ffffffffff
header: ccffffffffffffffffffff
kid: 0x000000ffffffffff
ctr: 0x0000010000000000
header: cdffffffffff010000000000
kid: 0x000000ffffffffff
ctr: 0x0000ffffffffffff
header: cdffffffffffffffffffffff
kid: 0x000000ffffffffff
ctr: 0x0001000000000000
header: ceffffffffff01000000000000
kid: 0x000000ffffffffff
ctr: 0x00ffffffffffffff
header: ceffffffffffffffffffffffff
kid: 0x000000ffffffffff
ctr: 0x0100000000000000
header: cfffffffffff0100000000000000
kid: 0x000000ffffffffff
ctr: 0xffffffffffffffff
header: cfffffffffffffffffffffffffff
kid: 0x0000010000000000
ctr: 0x0000000000000000
header: d0010000000000
kid: 0x0000010000000000
ctr: 0x0000000000000001
header: d1010000000000
kid: 0x0000010000000000
ctr: 0x00000000000000ff
header: d8010000000000ff
kid: 0x0000010000000000
ctr: 0x0000000000000100
header: d90100000000000100
kid: 0x0000010000000000
ctr: 0x000000000000ffff
header: d9010000000000ffff
kid: 0x0000010000000000
ctr: 0x0000000000010000
header: da010000000000010000
kid: 0x0000010000000000
ctr: 0x0000000000ffffff
header: da010000000000ffffff
kid: 0x0000010000000000
ctr: 0x0000000001000000
header: db01000000000001000000
kid: 0x0000010000000000
ctr: 0x00000000ffffffff
header: db010000000000ffffffff
kid: 0x0000010000000000
ctr: 0x0000000100000000
header: dc0100000000000100000000
kid: 0x0000010000000000
ctr: 0x000000ffffffffff
header: dc010000000000ffffffffff
kid: 0x0000010000000000
ctr: 0x0000010000000000
header: dd010000000000010000000000
kid: 0x0000010000000000
ctr: 0x0000ffffffffffff
header: dd010000000000ffffffffffff
kid: 0x0000010000000000
ctr: 0x0001000000000000
header: de01000000000001000000000000
kid: 0x0000010000000000
ctr: 0x00ffffffffffffff
header: de010000000000ffffffffffffff
kid: 0x0000010000000000
ctr: 0x0100000000000000
header: df0100000000000100000000000000
kid: 0x0000010000000000
ctr: 0xffffffffffffffff
header: df010000000000ffffffffffffffff
kid: 0x0000ffffffffffff
ctr: 0x0000000000000000
header: d0ffffffffffff
kid: 0x0000ffffffffffff
ctr: 0x0000000000000001
header: d1ffffffffffff
kid: 0x0000ffffffffffff
ctr: 0x00000000000000ff
header: d8ffffffffffffff
kid: 0x0000ffffffffffff
ctr: 0x0000000000000100
header: d9ffffffffffff0100
kid: 0x0000ffffffffffff
ctr: 0x000000000000ffff
header: d9ffffffffffffffff
kid: 0x0000ffffffffffff
ctr: 0x0000000000010000
header: daffffffffffff010000
kid: 0x0000ffffffffffff
ctr: 0x0000000000ffffff
header: daffffffffffffffffff
kid: 0x0000ffffffffffff
ctr: 0x0000000001000000
header: dbffffffffffff01000000
kid: 0x0000ffffffffffff
ctr: 0x00000000ffffffff
header: dbffffffffffffffffffff
kid: 0x0000ffffffffffff
ctr: 0x0000000100000000
header: dcffffffffffff0100000000
kid: 0x0000ffffffffffff
ctr: 0x000000ffffffffff
header: dcffffffffffffffffffffff
kid: 0x0000ffffffffffff
ctr: 0x0000010000000000
header: ddffffffffffff010000000000
kid: 0x0000ffffffffffff
ctr: 0x0000ffffffffffff
header: ddffffffffffffffffffffffff
kid: 0x0000ffffffffffff
ctr: 0x0001000000000000
header: deffffffffffff01000000000000
kid: 0x0000ffffffffffff
ctr: 0x00ffffffffffffff
header: deffffffffffffffffffffffffff
kid: 0x0000ffffffffffff
ctr: 0x0100000000000000
header: dfffffffffffff0100000000000000
kid: 0x0000ffffffffffff
ctr: 0xffffffffffffffff
header: dfffffffffffffffffffffffffffff
kid: 0x0001000000000000
ctr: 0x0000000000000000
header: e001000000000000
kid: 0x0001000000000000
ctr: 0x0000000000000001
header: e101000000000000
kid: 0x0001000000000000
ctr: 0x00000000000000ff
header: e801000000000000ff
kid: 0x0001000000000000
ctr: 0x0000000000000100
header: e9010000000000000100
kid: 0x0001000000000000
ctr: 0x000000000000ffff
header: e901000000000000ffff
kid: 0x0001000000000000
ctr: 0x0000000000010000
header: ea01000000000000010000
kid: 0x0001000000000000
ctr: 0x0000000000ffffff
header: ea01000000000000ffffff
kid: 0x0001000000000000
ctr: 0x0000000001000000
header: eb0100000000000001000000
kid: 0x0001000000000000
ctr: 0x00000000ffffffff
header: eb01000000000000ffffffff
kid: 0x0001000000000000
ctr: 0x0000000100000000
header: ec010000000000000100000000
kid: 0x0001000000000000
ctr: 0x000000ffffffffff
header: ec01000000000000ffffffffff
kid: 0x0001000000000000
ctr: 0x0000010000000000
header: ed01000000000000010000000000
kid: 0x0001000000000000
ctr: 0x0000ffffffffffff
header: ed01000000000000ffffffffffff
kid: 0x0001000000000000
ctr: 0x0001000000000000
header: ee0100000000000001000000000000
kid: 0x0001000000000000
ctr: 0x00ffffffffffffff
header: ee01000000000000ffffffffffffff
kid: 0x0001000000000000
ctr: 0x0100000000000000
header: ef010000000000000100000000000000
kid: 0x0001000000000000
ctr: 0xffffffffffffffff
header: ef01000000000000ffffffffffffffff
kid: 0x00ffffffffffffff
ctr: 0x0000000000000000
header: e0ffffffffffffff
kid: 0x00ffffffffffffff
ctr: 0x0000000000000001
header: e1ffffffffffffff
kid: 0x00ffffffffffffff
ctr: 0x00000000000000ff
header: e8ffffffffffffffff
kid: 0x00ffffffffffffff
ctr: 0x0000000000000100
header: e9ffffffffffffff0100
kid: 0x00ffffffffffffff
ctr: 0x000000000000ffff
header: e9ffffffffffffffffff
kid: 0x00ffffffffffffff
ctr: 0x0000000000010000
header: eaffffffffffffff010000
kid: 0x00ffffffffffffff
ctr: 0x0000000000ffffff
header: eaffffffffffffffffffff
kid: 0x00ffffffffffffff
ctr: 0x0000000001000000
header: ebffffffffffffff01000000
kid: 0x00ffffffffffffff
ctr: 0x00000000ffffffff
header: ebffffffffffffffffffffff
kid: 0x00ffffffffffffff
ctr: 0x0000000100000000
header: ecffffffffffffff0100000000
kid: 0x00ffffffffffffff
ctr: 0x000000ffffffffff
header: ecffffffffffffffffffffffff
kid: 0x00ffffffffffffff
ctr: 0x0000010000000000
header: edffffffffffffff010000000000
kid: 0x00ffffffffffffff
ctr: 0x0000ffffffffffff
header: edffffffffffffffffffffffffff
kid: 0x00ffffffffffffff
ctr: 0x0001000000000000
header: eeffffffffffffff01000000000000
kid: 0x00ffffffffffffff
ctr: 0x00ffffffffffffff
header: eeffffffffffffffffffffffffffff
kid: 0x00ffffffffffffff
ctr: 0x0100000000000000
header: efffffffffffffff0100000000000000
kid: 0x00ffffffffffffff
ctr: 0xffffffffffffffff
header: efffffffffffffffffffffffffffffff
kid: 0x0100000000000000
ctr: 0x0000000000000000
header: f00100000000000000
kid: 0x0100000000000000
ctr: 0x0000000000000001
header: f10100000000000000
kid: 0x0100000000000000
ctr: 0x00000000000000ff
header: f80100000000000000ff
kid: 0x0100000000000000
ctr: 0x0000000000000100
header: f901000000000000000100
kid: 0x0100000000000000
ctr: 0x000000000000ffff
header: f90100000000000000ffff
kid: 0x0100000000000000
ctr: 0x0000000000010000
header: fa0100000000000000010000
kid: 0x0100000000000000
ctr: 0x0000000000ffffff
header: fa0100000000000000ffffff
kid: 0x0100000000000000
ctr: 0x0000000001000000
header: fb010000000000000001000000
kid: 0x0100000000000000
ctr: 0x00000000ffffffff
header: fb0100000000000000ffffffff
kid: 0x0100000000000000
ctr: 0x0000000100000000
header: fc01000000000000000100000000
kid: 0x0100000000000000
ctr: 0x000000ffffffffff
header: fc0100000000000000ffffffffff
kid: 0x0100000000000000
ctr: 0x0000010000000000
header: fd0100000000000000010000000000
kid: 0x0100000000000000
ctr: 0x0000ffffffffffff
header: fd0100000000000000ffffffffffff
kid: 0x0100000000000000
ctr: 0x0001000000000000
header: fe010000000000000001000000000000
kid: 0x0100000000000000
ctr: 0x00ffffffffffffff
header: fe0100000000000000ffffffffffffff
kid: 0x0100000000000000
ctr: 0x0100000000000000
header: ff010000000000000001000000000000
00
kid: 0x0100000000000000
ctr: 0xffffffffffffffff
header: ff0100000000000000ffffffffffffff
ff
kid: 0xffffffffffffffff
ctr: 0x0000000000000000
header: f0ffffffffffffffff
kid: 0xffffffffffffffff
ctr: 0x0000000000000001
header: f1ffffffffffffffff
kid: 0xffffffffffffffff
ctr: 0x00000000000000ff
header: f8ffffffffffffffffff
kid: 0xffffffffffffffff
ctr: 0x0000000000000100
header: f9ffffffffffffffff0100
kid: 0xffffffffffffffff
ctr: 0x000000000000ffff
header: f9ffffffffffffffffffff
kid: 0xffffffffffffffff
ctr: 0x0000000000010000
header: faffffffffffffffff010000
kid: 0xffffffffffffffff
ctr: 0x0000000000ffffff
header: faffffffffffffffffffffff
kid: 0xffffffffffffffff
ctr: 0x0000000001000000
header: fbffffffffffffffff01000000
kid: 0xffffffffffffffff
ctr: 0x00000000ffffffff
header: fbffffffffffffffffffffffff
kid: 0xffffffffffffffff
ctr: 0x0000000100000000
header: fcffffffffffffffff0100000000
kid: 0xffffffffffffffff
ctr: 0x000000ffffffffff
header: fcffffffffffffffffffffffffff
kid: 0xffffffffffffffff
ctr: 0x0000010000000000
header: fdffffffffffffffff010000000000
kid: 0xffffffffffffffff
ctr: 0x0000ffffffffffff
header: fdffffffffffffffffffffffffffff
kid: 0xffffffffffffffff
ctr: 0x0001000000000000
header: feffffffffffffffff01000000000000
kid: 0xffffffffffffffff
ctr: 0x00ffffffffffffff
header: feffffffffffffffffffffffffffffff
kid: 0xffffffffffffffff
ctr: 0x0100000000000000
header: ffffffffffffffffff01000000000000
00
kid: 0xffffffffffffffff
ctr: 0xffffffffffffffff
header: ffffffffffffffffffffffffffffffff
ff
C.2. AEAD Encryption/Decryption Using AES-CTR and HMAC
For each case, we provide:
* cipher_suite: The index of the cipher suite in use (see
Section 8.1)
* key: The key input to encryption/decryption
* enc_key: The encryption subkey produced by the derive_subkeys()
algorithm
* auth_key: The encryption subkey produced by the derive_subkeys()
algorithm
* nonce: The nonce input to encryption/decryption
* aad: The aad input to encryption/decryption
* pt: The plaintext
* ct: The ciphertext
An implementation should verify that the following are true, where
AEAD.Encrypt and AEAD.Decrypt are as defined in Section 4.5.1:
* AEAD.Encrypt(key, nonce, aad, pt) == ct
* AEAD.Decrypt(key, nonce, aad, ct) == pt
The other values in the test vector are intermediate values provided
to facilitate debugging of test failures.
cipher_suite: 0x0001
key: 000102030405060708090a0b0c0d0e0f
101112131415161718191a1b1c1d1e1f
202122232425262728292a2b2c2d2e2f
enc_key: 000102030405060708090a0b0c0d0e0f
auth_key: 101112131415161718191a1b1c1d1e1f
202122232425262728292a2b2c2d2e2f
nonce: 101112131415161718191a1b
aad: 4945544620534672616d65205747
pt: 64726166742d696574662d736672616d
652d656e63
ct: 6339af04ada1d064688a442b8dc69d5b
6bfa40f4bef0583e8081069cc60705
cipher_suite: 0x0002
key: 000102030405060708090a0b0c0d0e0f
101112131415161718191a1b1c1d1e1f
202122232425262728292a2b2c2d2e2f
enc_key: 000102030405060708090a0b0c0d0e0f
auth_key: 101112131415161718191a1b1c1d1e1f
202122232425262728292a2b2c2d2e2f
nonce: 101112131415161718191a1b
aad: 4945544620534672616d65205747
pt: 64726166742d696574662d736672616d
652d656e63
ct: 6339af04ada1d064688a442b8dc69d5b
6bfa40f4be6e93b7da076927bb
cipher_suite: 0x0003
key: 000102030405060708090a0b0c0d0e0f
101112131415161718191a1b1c1d1e1f
202122232425262728292a2b2c2d2e2f
enc_key: 000102030405060708090a0b0c0d0e0f
auth_key: 101112131415161718191a1b1c1d1e1f
202122232425262728292a2b2c2d2e2f
nonce: 101112131415161718191a1b
aad: 4945544620534672616d65205747
pt: 64726166742d696574662d736672616d
652d656e63
ct: 6339af04ada1d064688a442b8dc69d5b
6bfa40f4be09480509
C.3. SFrame Encryption/Decryption
For each case, we provide:
* cipher_suite: The index of the cipher suite in use (see
Section 8.1)
* kid: A KID value
* ctr: A CTR value
* base_key: The base_key input to the derive_key_salt algorithm
* sframe_key_label: The label used to derive sframe_key in the
derive_key_salt algorithm
* sframe_salt_label: The label used to derive sframe_salt in the
derive_key_salt algorithm
* sframe_secret: The sframe_secret variable in the derive_key_salt
algorithm
* sframe_key: The sframe_key value produced by the derive_key_salt
algorithm
* sframe_salt: The sframe_salt value produced by the derive_key_salt
algorithm
* metadata: The metadata input to the SFrame encrypt algorithm
* pt: The plaintext
* ct: The SFrame ciphertext
An implementation should verify that the following are true, where
encrypt and decrypt are as defined in Section 4.4, using an SFrame
context initialized with base_key assigned to kid:
* encrypt(ctr, kid, metadata, plaintext) == ct
* decrypt(metadata, ct) == pt
The other values in the test vector are intermediate values provided
to facilitate debugging of test failures.
cipher_suite: 0x0001
kid: 0x0000000000000123
ctr: 0x0000000000004567
base_key: 000102030405060708090a0b0c0d0e0f
sframe_key_label: 534672616d6520312e30205365637265
74206b65792000000000000001230001
sframe_salt_label: 534672616d6520312e30205365637265
742073616c7420000000000000012300
01
sframe_secret: d926952ca8b7ec4a95941d1ada3a5203
ceff8cceee34f574d23909eb314c40c0
sframe_key: 3f7d9a7c83ae8e1c8a11ae695ab59314
b367e359fadac7b9c46b2bc6f81f46e1
6b96f0811868d59402b7e870102720b3
sframe_salt: 50b29329a04dc0f184ac3168
metadata: 4945544620534672616d65205747
nonce: 50b29329a04dc0f184ac740f
aad: 99012345674945544620534672616d65
205747
pt: 64726166742d696574662d736672616d
652d656e63
ct: 9901234567449408b6f490086165b9d6
f62b24ae1a59a56486b4ae8ed036b889
12e24f11
cipher_suite: 0x0002
kid: 0x0000000000000123
ctr: 0x0000000000004567
base_key: 000102030405060708090a0b0c0d0e0f
sframe_key_label: 534672616d6520312e30205365637265
74206b65792000000000000001230002
sframe_salt_label: 534672616d6520312e30205365637265
742073616c7420000000000000012300
02
sframe_secret: d926952ca8b7ec4a95941d1ada3a5203
ceff8cceee34f574d23909eb314c40c0
sframe_key: e2ec5c797540310483b16bf6e7a570d2
a27d192fe869c7ccd8584a8d9dab9154
9fbe553f5113461ec6aa83bf3865553e
sframe_salt: e68ac8dd3d02fbcd368c5577
metadata: 4945544620534672616d65205747
nonce: e68ac8dd3d02fbcd368c1010
aad: 99012345674945544620534672616d65
205747
pt: 64726166742d696574662d736672616d
652d656e63
ct: 99012345673f31438db4d09434e43afa
0f8a2f00867a2be085046a9f5cb4f101
d607
cipher_suite: 0x0003
kid: 0x0000000000000123
ctr: 0x0000000000004567
base_key: 000102030405060708090a0b0c0d0e0f
sframe_key_label: 534672616d6520312e30205365637265
74206b65792000000000000001230003
sframe_salt_label: 534672616d6520312e30205365637265
742073616c7420000000000000012300
03
sframe_secret: d926952ca8b7ec4a95941d1ada3a5203
ceff8cceee34f574d23909eb314c40c0
sframe_key: 2c5703089cbb8c583475e4fc461d97d1
8809df79b6d550f78eb6d50ffa80d892
11d57909934f46f5405e38cd583c69fe
sframe_salt: 38c16e4f5159700c00c7f350
metadata: 4945544620534672616d65205747
nonce: 38c16e4f5159700c00c7b637
aad: 99012345674945544620534672616d65
205747
pt: 64726166742d696574662d736672616d
652d656e63
ct: 990123456717fc8af28a5a695afcfc6c
8df6358a17e26b2fcb3bae32e443
cipher_suite: 0x0004
kid: 0x0000000000000123
ctr: 0x0000000000004567
base_key: 000102030405060708090a0b0c0d0e0f
sframe_key_label: 534672616d6520312e30205365637265
74206b65792000000000000001230004
sframe_salt_label: 534672616d6520312e30205365637265
742073616c7420000000000000012300
04
sframe_secret: d926952ca8b7ec4a95941d1ada3a5203
ceff8cceee34f574d23909eb314c40c0
sframe_key: d34f547f4ca4f9a7447006fe7fcbf768
sframe_salt: 75234edefe07819026751816
metadata: 4945544620534672616d65205747
nonce: 75234edefe07819026755d71
aad: 99012345674945544620534672616d65
205747
pt: 64726166742d696574662d736672616d
652d656e63
ct: 9901234567b7412c2513a1b66dbb4884
1bbaf17f598751176ad847681a69c6d0
b091c07018ce4adb34eb
cipher_suite: 0x0005
kid: 0x0000000000000123
ctr: 0x0000000000004567
base_key: 000102030405060708090a0b0c0d0e0f
sframe_key_label: 534672616d6520312e30205365637265
74206b65792000000000000001230005
sframe_salt_label: 534672616d6520312e30205365637265
742073616c7420000000000000012300
05
sframe_secret: 0fc3ea6de6aac97a35f194cf9bed94d4
b5230f1cb45a785c9fe5dce9c188938a
b6ba005bc4c0a19181599e9d1bcf7b74
aca48b60bf5e254e546d809313e083a3
sframe_key: d3e27b0d4a5ae9e55df01a70e6d4d28d
969b246e2936f4b7a5d9b494da6b9633
sframe_salt: 84991c167b8cd23c93708ec7
metadata: 4945544620534672616d65205747
nonce: 84991c167b8cd23c9370cba0
aad: 99012345674945544620534672616d65
205747
pt: 64726166742d696574662d736672616d
652d656e63
ct: 990123456794f509d36e9beacb0e261d
99c7d1e972f1fed787d4049f17ca2135
3c1cc24d56ceabced279
Acknowledgements
The authors wish to specially thank Dr. Alex Gouaillard as one of the
early contributors to the document. His passion and energy were key
to the design and development of SFrame.
Contributors
Frédéric Jacobs
Apple
Email: frederic.jacobs@apple.com
Marta Mularczyk
Amazon
Email: mulmarta@amazon.com
Suhas Nandakumar
Cisco
Email: snandaku@cisco.com
Tomas Rigaux
Cisco
Email: trigaux@cisco.com
Raphael Robert
Phoenix R&D
Email: ietf@raphaelrobert.com
Authors' Addresses
Emad Omara
Apple
Email: eomara@apple.com
Justin Uberti
Fixie.ai
Email: justin@fixie.ai
Sergio Garcia Murillo
CoSMo Software
Email: sergio.garcia.murillo@cosmosoftware.io
Richard Barnes (editor)
Cisco
Email: rlb@ipv.sx
Youenn Fablet
Apple
Email: youenn@apple.com
ERRATA