Internet DRAFT - draft-thomson-http-encryption
draft-thomson-http-encryption
Network Working Group M. Thomson
Internet-Draft Mozilla
Intended status: Standards Track October 19, 2015
Expires: April 21, 2016
Encrypted Content-Encoding for HTTP
draft-thomson-http-encryption-02
Abstract
This memo introduces a content-coding for HTTP that allows message
payloads to be encrypted.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on April 21, 2016.
Copyright Notice
Copyright (c) 2015 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. The "aesgcm128" HTTP Content Encoding . . . . . . . . . . . . 3
3. The Encryption HTTP Header Field . . . . . . . . . . . . . . 5
3.1. Encryption Header Field Parameters . . . . . . . . . . . 6
3.2. Content Encryption Key Derivation . . . . . . . . . . . . 6
3.3. Nonce Derivation . . . . . . . . . . . . . . . . . . . . 7
4. Encryption-Key Header Field . . . . . . . . . . . . . . . . . 7
4.1. Explicit Key . . . . . . . . . . . . . . . . . . . . . . 8
4.2. Diffie-Hellman . . . . . . . . . . . . . . . . . . . . . 8
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Successful GET Response . . . . . . . . . . . . . . . . . 9
5.2. Encryption and Compression . . . . . . . . . . . . . . . 9
5.3. Encryption with More Than One Key . . . . . . . . . . . . 9
5.4. Encryption with Explicit Key . . . . . . . . . . . . . . 10
5.5. Diffie-Hellman Encryption . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6.1. Key and Nonce Reuse . . . . . . . . . . . . . . . . . . . 11
6.2. Content Integrity . . . . . . . . . . . . . . . . . . . . 12
6.3. Leaking Information in Headers . . . . . . . . . . . . . 12
6.4. Poisoning Storage . . . . . . . . . . . . . . . . . . . . 13
6.5. Sizing and Timing Attacks . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7.1. The "aesgcm128" HTTP Content Encoding . . . . . . . . . . 13
7.2. Encryption Header Fields . . . . . . . . . . . . . . . . 13
7.3. The HTTP Encryption Parameter Registry . . . . . . . . . 14
7.3.1. keyid . . . . . . . . . . . . . . . . . . . . . . . . 14
7.3.2. salt . . . . . . . . . . . . . . . . . . . . . . . . 14
7.3.3. rs . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.4. The HTTP Encryption-Key Parameter Registry . . . . . . . 15
7.4.1. keyid . . . . . . . . . . . . . . . . . . . . . . . . 15
7.4.2. aesgcm128 . . . . . . . . . . . . . . . . . . . . . . 15
7.4.3. dh . . . . . . . . . . . . . . . . . . . . . . . . . 16
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.1. Normative References . . . . . . . . . . . . . . . . . . 16
8.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. JWE Mapping . . . . . . . . . . . . . . . . . . . . 18
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 19
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
It is sometimes desirable to encrypt the contents of a HTTP message
(request or response) so that when the payload is stored (e.g., with
a HTTP PUT), only someone with the appropriate key can read it.
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For example, it might be necessary to store a file on a server
without exposing its contents to that server. Furthermore, that same
file could be replicated to other servers (to make it more resistant
to server or network failure), downloaded by clients (to make it
available offline), etc. without exposing its contents.
These uses are not met by the use of TLS [RFC5246], since it only
encrypts the channel between the client and server.
This document specifies a content-coding (Section 3.1.2 of [RFC7231])
for HTTP to serve these and other use cases.
This content-coding is not a direct adaptation of message-based
encryption formats - such as those that are described by [RFC4880],
[RFC5652], [RFC7516], and [XMLENC] - which are not suited to stream
processing, which is necessary for HTTP. The format described here
cleaves more closely to the lower level constructs described in
[RFC5116].
To the extent that message-based encryption formats use the same
primitives, the format can be considered as sequence of encrypted
messages with a particular profile. For instance, Appendix A
explains how the format is congruent with a sequence of JSON Web
Encryption [RFC7516] values with a fixed header.
This mechanism is likely only a small part of a larger design that
uses content encryption. How clients and servers acquire and
identify keys will depend on the use case. Though a complete key
management system is not described, this document defines an
Encryption-Key header field that can be used to convey keying
material.
1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. The "aesgcm128" HTTP Content Encoding
The "aesgcm128" HTTP content-coding indicates that a payload has been
encrypted using Advanced Encryption Standard (AES) in Galois/Counter
Mode (GCM) as identified as AEAD_AES_128_GCM in [RFC5116],
Section 5.1. The AEAD_AES_128_GCM algorithm uses a 128 bit content
encryption key.
When this content-coding is in use, the Encryption header field
(Section 3) describes how encryption has been applied. The
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Encryption-Key header field (Section 4) can be included to describe
how the content encryption key is derived or retrieved.
The "aesgcm128" content-coding uses a single fixed set of encryption
primitives. Cipher suite agility is achieved by defining a new
content-coding scheme. This ensures that only the HTTP Accept-
Encoding header field is necessary to negotiate the use of
encryption.
The "aesgcm128" content-coding uses a fixed record size. The
resulting encoding is a series of fixed-size records, with a final
record that is one or more octets shorter than a fixed sized record.
+------+ input of between rs-256
| data | and rs-1 octets
+------+ (one fewer for the last record)
|
v
+-----+-----------+
| pad | data | add padding to form plaintext
+-----+-----------+
|
v
+--------------------+
| ciphertext | encrypt with AEAD_AES_128_GCM
+--------------------+ expands by 16 octets
The record size determines the length of each portion of plaintext
that is enciphered, with the exception of the final record, which is
necessarily smaller. The record size defaults to 4096 octets, but
can be changed using the "rs" parameter on the Encryption header
field.
AEAD_AES_128_GCM expands ciphertext to be 16 octets longer than its
input plaintext. Therefore, the length of each enciphered record
other than the last is equal to the value of the "rs" parameter plus
16 octets. A receiver MUST fail to decrypt if the final record
ciphertext is 16 octets or less in size. Valid records always
contain at least one byte of padding and a 16 octet authentication
tag.
Each record contains between 1 and 256 octets of padding, inserted
into a record before the enciphered content. Padding consists of a
length byte, followed that number of zero-valued octets. A receiver
MUST fail to decrypt if any padding octet other than the first is
non-zero, or a record has more padding than the record size can
accommodate.
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The nonce for each record is a 96-bit value constructed from the
record sequence number and the input keying material. Nonce
derivation is covered in Section 3.3.
The additional data passed to each invocation of AEAD_AES_128_GCM is
a zero-length octet sequence.
A sequence of full-sized records can be truncated to produce a
shorter sequence of records with valid authentication tags. To
prevent an attacker from truncating a stream, an encoder MUST append
a record that contains only padding and is smaller than the full
record size if the final record ends on a record boundary. A
receiver MUST treat the stream as failed due to truncation if the
final record is the full record size.
A consequence of this record structure is that range requests
[RFC7233] and random access to encrypted payload bodies are possible
at the granularity of the record size. However, without data from
adjacent ranges, partial records cannot be used. Thus, it is best if
records start and end on multiples of the record size, plus the 16
octet authentication tag size.
3. The Encryption HTTP Header Field
The "Encryption" HTTP header field describes the encrypted content
encoding(s) that have been applied to a payload body, and therefore
how those content encoding(s) can be removed.
The "Encryption" header field uses the extended ABNF syntax defined
in Section 1.2 of [RFC7230] and the "parameter" rule from [RFC7231]
Encryption-val = #encryption_params
encryption_params = [ parameter *( ";" parameter ) ]
If the payload is encrypted more than once (as reflected by having
multiple content-codings that imply encryption), each application of
the content encoding is reflected in the Encryption header field, in
the order in which they were applied.
The Encryption header MAY be omitted if the sender does not intend
for the immediate recipient to be able to decrypt the payload body.
Alternatively, the Encryption header field MAY be omitted if the
sender intends for the recipient to acquire the header field by other
means.
Servers processing PUT requests MUST persist the value of the
Encryption header field, unless they remove the content-coding by
decrypting the payload.
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3.1. Encryption Header Field Parameters
The following parameters are used in determining the content
encryption key that is used for encryption:
keyid: The "keyid" parameter contains a string that identifies the
keying material that is used. The "keyid" parameter SHOULD be
included, unless key identification is guaranteed by other means.
The "keyid" parameter MUST be used if keying material included in
an Encryption-Key header field is needed to derive the content
encryption key.
salt: The "salt" parameter contains a base64 URL-encoded octets that
is used as salt in deriving a unique content encryption key (see
Section 3.2). The "salt" parameter MUST be present, and MUST be
exactly 16 octets long when decoded. The "salt" parameter MUST
NOT be reused for two different payload bodies that have the same
input keying material; generating a random salt for every
application of the content encoding ensures that content
encryption key reuse is highly unlikely.
rs: The "rs" parameter contains a positive decimal integer that
describes the record size in octets. This value MUST be greater
than 1. If the "rs" parameter is absent, the record size defaults
to 4096 octets.
3.2. Content Encryption Key Derivation
In order to allow the reuse of keying material for multiple different
HTTP messages, a content encryption key is derived for each message.
The content encryption key is derived from the decoded value of the
"salt" parameter using the HMAC-based key derivation function (HKDF)
described in [RFC5869] using the SHA-256 hash algorithm [FIPS180-2].
The decoded value of the "salt" parameter is the salt input to HKDF
function. The keying material identified by the "keyid" parameter is
the input keying material (IKM) to HKDF. Input keying material can
either be prearranged, or can be described using the Encryption-Key
header field (Section 4). The first step of HKDF is therefore:
PRK = HMAC-SHA-256(salt, IKM)
AEAD_AES_128_GCM requires a 16 octet (128 bit) content encryption
key, so the length (L) parameter to HKDF is 16. The info parameter
is set to the ASCII-encoded string "Content-Encoding: aesgcm128".
The second step of HKDF can therefore be simplified to the first 16
octets of a single HMAC:
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CEK = HMAC-SHA-256(PRK, "Content-Encoding: aesgcm128" || 0x01)
3.3. Nonce Derivation
The nonce input to AEAD_AES_128_GCM is constructed for each record.
The nonce for each record is a 12 octet (96 bit) value is produced
from the record sequence number and a value derived from the input
keying material.
The input keying material and salt values are input to HKDF with
different info and length parameters. The info parameter for the
nonce is the ASCII-encoded string "Content-Encoding: nonce" and the
length (L) parameter is 12 octets.
The result is combined with the record sequence number - using
exclusive or - to produce the nonce. The record sequence number
(SEQ) is a 96-bit unsigned integer in network byte order that starts
at zero.
Thus, the final nonce for each record is a 12 octet value:
NONCE = HMAC-SHA-256(PRK, "Content-Encoding: nonce" || 0x01) ^ SEQ
4. Encryption-Key Header Field
An Encryption-Key header field can be used to describe the input
keying material used in the Encryption header field.
The Encryption-Key header field uses the extended ABNF syntax defined
in Section 1.2 of [RFC7230] and the "parameter" rule from [RFC7231].
Encryption-Key-val = #encryption_key_params
encryption_key_params = [ parameter *( ";" parameter ) ]
keyid: The "keyid" parameter corresponds to the "keyid" parameter in
the Encryption header field.
aesgcm128: The "aesgcm128" parameter contains the URL-safe base64
[RFC4648] octets of the input keying material.
dh: The "dh" parameter contains an ephemeral Diffie-Hellman share.
This form of the header field can be used to encrypt content for a
specific recipient.
The input keying material used by the content-encoding key derivation
(see Section 3.2) can be determined based on the information in the
Encryption-Key header field. The method for key derivation depends
on the parameters that are present in the header field.
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The value or values provided in the Encryption-Key header field is
valid only for the current HTTP message unless additional information
indicates a greater scope.
Note that different methods for determining input keying material
will produce different amounts of data. The HKDF process ensures
that the final content encryption key is the necessary size.
Alternative methods for determining input keying material MAY be
defined by specifications that use this content-encoding.
4.1. Explicit Key
The "aesgcm128" parameter is decoded and used as the input keying
material for the "aesgcm128" content encoding. The "aesgcm128"
parameter MUST decode to at least 16 octets in order to be used as
input keying material for "aesgcm128" content encoding.
Other key determination parameters can be ignored if the "aesgcm128"
parameter is present.
4.2. Diffie-Hellman
The "dh" parameter is included to describe a Diffie-Hellman share,
either modp (or finite field) Diffie-Hellman [DH] or elliptic curve
Diffie-Hellman (ECDH) [RFC4492].
This share is combined with other information at the recipient to
determine the HKDF input keying material. In order for the exchange
to be successful, the following information MUST be established out
of band:
o Which Diffie-Hellman form is used.
o The modp group or elliptic curve that will be used.
o The format of the ephemeral public share that is included in the
"dh" parameter. For instance, using ECDH both parties need to
agree whether this is an uncompressed or compressed point.
In addition to identifying which content-encoding this input keying
material is used for, the "keyid" parameter is used to identify this
additional information at the receiver.
The intended recipient recovers their private key and are then able
to generate a shared secret using the appropriate Diffie-Hellman
process.
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Specifications that rely on an Diffie-Hellman exchange for
determining input keying material MUST either specify the parameters
for Diffie-Hellman (group parameters, or curves and point format)
that are used, or describe how those parameters are negotiated
between sender and receiver.
5. Examples
5.1. Successful GET Response
HTTP/1.1 200 OK
Content-Type: application/octet-stream
Content-Encoding: aesgcm128
Connection: close
Encryption: keyid="http://example.org/bob/keys/123";
salt="XZwpw6o37R-6qoZjw6KwAw"
[encrypted payload]
Here, a successful HTTP GET response has been encrypted using input
keying material that is identified by a URI.
Note that the media type has been changed to "application/octet-
stream" to avoid exposing information about the content.
5.2. Encryption and Compression
HTTP/1.1 200 OK
Content-Type: text/html
Content-Encoding: aesgcm128, gzip
Transfer-Encoding: chunked
Encryption: keyid="mailto:me@example.com";
salt="m2hJ_NttRtFyUiMRPwfpHA"
[encrypted payload]
5.3. Encryption with More Than One Key
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PUT /thing HTTP/1.1
Host: storage.example.com
Content-Type: application/http
Content-Encoding: aesgcm128, aesgcm128
Content-Length: 1234
Encryption: keyid="mailto:me@example.com";
salt="NfzOeuV5USPRA-n_9s1Lag",
keyid="http://example.org/bob/keys/123";
salt="bDMSGoc2uobK_IhavSHsHA"; rs=1200
[encrypted payload]
Here, a PUT request has been encrypted twice with different input
keying material; decrypting twice is necessary to read the content.
The outer layer of encryption uses a 1200 octet record size.
5.4. Encryption with Explicit Key
HTTP/1.1 200 OK
Content-Length: 32
Content-Encoding: aesgcm128
Encryption: keyid="a1"; salt="ibZx1RNz537h1XNkRcPpjA"
Encryption-Key: keyid="a1"; aesgcm128="9Z57YCb3dK95dSsdFJbkag"
zK3kpG__Z8whjIkG6RYgPz11oUkTKcxPy9WP-VPMfuc
This example shows the string "I am the walrus" encrypted using an
directly provided value for the input keying material. The content
body contains a single record only and is shown here encoded in URL-
safe base64 for presentation reasons only.
5.5. Diffie-Hellman Encryption
HTTP/1.1 200 OK
Content-Length: 32
Content-Encoding: aesgcm128
Encryption: keyid="dhkey"; salt="5hpuYfxDzG6nSs9-EQuaBg"
Encryption-Key: keyid="dhkey";
dh="BLsyIPbDn6bquEOwHaju2gj8kUVoflzTtPs_6fGoock_
dwxi1BcgFtObPVnic4alcEucx8I6G8HmEZCJnAl36Zg"
BmuHqRzdD4W1mibxglrPiRHZRSY49Dzdm6jHrWXzZrE
This example shows the same string, "I am the walrus", encrypted
using ECDH over the P-256 curve [FIPS186]. The content body is shown
here encoded in URL-safe base64 for presentation reasons only.
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The receiver (in this case, the HTTP client) uses a key pair that is
identified by the string "dhkey" and the sender (the server) uses a
key pair for which the public share is included in the "dh" parameter
above. The keys shown below use uncompressed points [X.692] encoded
using URL-safe base64. Line wrapping is added for presentation
purposes only.
Receiver:
private key: iCjNf8v4ox_g1rJuSs_gbNmYuUYx76ZRruQs_CHRzDg
public key: BPM1w41cSD4BMeBTY0Fz9ryLM-LeM22Dvt0gaLRukf05
rMhzFAvxVW_mipg5O0hkWad9ZWW0uMRO2Nrd32v8odQ
Sender:
private key: W0cxgeHDZkR3uMQYAbVgF5swKQUAR7DgoTaaQVlA-Fg
public key: <the value of the "dh" parameter>
6. Security Considerations
This mechanism assumes the presence of a key management framework
that is used to manage the distribution of keys between valid senders
and receivers. Defining key management is part of composing this
mechanism into a larger application, protocol, or framework.
Implementation of cryptography - and key management in particular -
can be difficult. For instance, implementations need to account for
the potential for exposing keying material on side channels, such as
might be exposed by the time it takes to perform a given operation.
The requirements for a good implementation of cryptographic
algorithms can change over time.
6.1. Key and Nonce Reuse
Encrypting different plaintext with the same content encryption key
and nonce in AES-GCM is not safe [RFC5116]. The scheme defined here
uses a fixed progression of nonce values. Thus, a new content
encryption key is needed for every application of the content
encoding. Since input keying material can be reused, a unique "salt"
parameter is needed to ensure a content encryption key is not reused.
If a content encryption key is reused - that is, if input keying
material and salt are reused - this could expose the plaintext and
the authentication key, nullifying the protection offered by
encryption. Thus, if the same input keying material is reused, then
the salt parameter MUST be unique each time. This ensures that the
content encryption key is not reused. An implementation SHOULD
generate a random salt parameter for every message; a counter could
achieve the same result.
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6.2. Content Integrity
This mechanism only provides content origin authentication. The
authentication tag only ensures that an entity with access to the
content encryption key produced the encrypted data.
Any entity with the content encryption key can therefore produce
content that will be accepted as valid. This includes all recipients
of the same HTTP message.
Furthermore, any entity that is able to modify both the Encryption
header field and the HTTP message body can replace the contents.
Without the content encryption key or the input keying material,
modifications to or replacement of parts of a payload body are not
possible.
6.3. Leaking Information in Headers
Because only the payload body is encrypted, information exposed in
header fields is visible to anyone who can read the HTTP message.
This could expose side-channel information.
For example, the Content-Type header field can leak information about
the payload body.
There are a number of strategies available to mitigate this threat,
depending upon the application's threat model and the users'
tolerance for leaked information:
1. Determine that it is not an issue. For example, if it is
expected that all content stored will be "application/json", or
another very common media type, exposing the Content-Type header
field could be an acceptable risk.
2. If it is considered sensitive information and it is possible to
determine it through other means (e.g., out of band, using hints
in other representations, etc.), omit the relevant headers, and/
or normalize them. In the case of Content-Type, this could be
accomplished by always sending Content-Type: application/octet-
stream (the most generic media type), or no Content-Type at all.
3. If it is considered sensitive information and it is not possible
to convey it elsewhere, encapsulate the HTTP message using the
application/http media type (Section 8.3.2 of [RFC7230]),
encrypting that as the payload of the "outer" message.
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6.4. Poisoning Storage
This mechanism only offers encryption of content; it does not perform
authentication or authorization, which still needs to be performed
(e.g., by HTTP authentication [RFC7235]).
This is especially relevant when a HTTP PUT request is accepted by a
server; if the request is unauthenticated, it becomes possible for a
third party to deny service and/or poison the store.
6.5. Sizing and Timing Attacks
Applications using this mechanism need to be aware that the size of
encrypted messages, as well as their timing, HTTP methods, URIs and
so on, may leak sensitive information.
This risk can be mitigated through the use of the padding that this
mechanism provides. Alternatively, splitting up content into
segments and storing the separately might reduce exposure. HTTP/2
[RFC7540] combined with TLS [RFC5246] might be used to hide the size
of individual messages.
7. IANA Considerations
7.1. The "aesgcm128" HTTP Content Encoding
This memo registers the "encrypted" HTTP content-coding in the HTTP
Content Codings Registry, as detailed in Section 2.
o Name: aesgcm128
o Description: AES-GCM encryption with a 128-bit content encryption
key
o Reference: this specification
7.2. Encryption Header Fields
This memo registers the "Encryption" HTTP header field in the
Permanent Message Header Registry, as detailed in Section 3.
o Field name: Encryption
o Protocol: HTTP
o Status: Standard
o Reference: this specification
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o Notes:
This memo registers the "Encryption-Key" HTTP header field in the
Permanent Message Header Registry, as detailed in Section 4.
o Field name: Encryption-Key
o Protocol: HTTP
o Status: Standard
o Reference: this specification
o Notes:
7.3. The HTTP Encryption Parameter Registry
This memo establishes a registry for parameters used by the
"Encryption" header field under the "Hypertext Transfer Protocol
(HTTP) Parameters" grouping. The "Hypertext Transfer Protocol (HTTP)
Encryption Parameters" operates under an "Specification Required"
policy [RFC5226].
Entries in this registry are expected to include the following
information:
o Parameter Name: The name of the parameter.
o Purpose: A brief description of the purpose of the parameter.
o Reference: A reference to a specification that defines the
semantics of the parameter.
The initial contents of this registry are:
7.3.1. keyid
o Parameter Name: keyid
o Purpose: Identify the key that is in use.
o Reference: this document
7.3.2. salt
o Parameter Name: salt
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o Purpose: Provide a source of entropy for derivation of a content
encryption key. This value is mandatory.
o Reference: this document
7.3.3. rs
o Parameter Name: rs
o Purpose: The size of the encrypted records.
o Reference: this document
7.4. The HTTP Encryption-Key Parameter Registry
This memo establishes a registry for parameters used by the
"Encryption-Key" header field under the "Hypertext Transfer Protocol
(HTTP) Parameters" grouping. The "Hypertext Transfer Protocol (HTTP)
Encryption Parameters" operates under an "Specification Required"
policy [RFC5226].
Entries in this registry are expected to include the following
information:
o Parameter Name: The name of the parameter.
o Purpose: A brief description of the purpose of the parameter.
o Reference: A reference to a specification that defines the
semantics of the parameter.
The initial contents of this registry are:
7.4.1. keyid
o Parameter Name: keyid
o Purpose: Identify the key that is in use.
o Reference: this document
7.4.2. aesgcm128
o Parameter Name: aesgcm128
o Purpose: Provide an explicit input keying material value for the
aesgcm128 content encoding.
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o Reference: this document
7.4.3. dh
o Parameter Name: dh
o Purpose: Carry a modp or elliptic curve Diffie-Hellman share used
to derive input keying material.
o Reference: this document
8. References
8.1. Normative References
[DH] Diffie, W. and M. Hellman, "New Directions in
Cryptography", IEEE Transactions on Information Theory,
V.IT-22 n.6 , June 1977.
[FIPS180-2]
Department of Commerce, National., "NIST FIPS 180-2,
Secure Hash Standard", August 2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492, DOI
10.17487/RFC4492, May 2006,
<http://www.rfc-editor.org/info/rfc4492>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<http://www.rfc-editor.org/info/rfc4648>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<http://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,
<http://www.rfc-editor.org/info/rfc5869>.
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[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing", RFC
7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI
10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>.
8.2. Informative References
[FIPS186] National Institute of Standards and Technology (NIST),
"Digital Signature Standard (DSS)", NIST PUB 186-4 , July
2013.
[RFC4880] Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R.
Thayer, "OpenPGP Message Format", RFC 4880, DOI 10.17487/
RFC4880, November 2007,
<http://www.rfc-editor.org/info/rfc4880>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/
RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<http://www.rfc-editor.org/info/rfc5652>.
[RFC7233] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
"Hypertext Transfer Protocol (HTTP/1.1): Range Requests",
RFC 7233, DOI 10.17487/RFC7233, June 2014,
<http://www.rfc-editor.org/info/rfc7233>.
[RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Authentication", RFC 7235, DOI
10.17487/RFC7235, June 2014,
<http://www.rfc-editor.org/info/rfc7235>.
[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
RFC 7516, DOI 10.17487/RFC7516, May 2015,
<http://www.rfc-editor.org/info/rfc7516>.
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[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540, DOI
10.17487/RFC7540, May 2015,
<http://www.rfc-editor.org/info/rfc7540>.
[X.692] ANSI, "Public Key Cryptography For The Financial Services
Industry: The Elliptic Curve Digital Signature Algorithm
(ECDSA)", ANSI X9.62 , 1998.
[XMLENC] Eastlake, D., Reagle, J., Imamura, T., Dillaway, B., and
E. Simon, "XML Encryption Syntax and Processing", W3C REC
, December 2002, <http://www.w3.org/TR/xmlenc-core/>.
Appendix A. JWE Mapping
The "aesgcm128" content encoding can be considered as a sequence of
JSON Web Encryption (JWE) objects [RFC7516], each corresponding to a
single fixed size record. The following transformations are applied
to a JWE object that might be expressed using the JWE Compact
Serialization:
o The JWE Protected Header is fixed to a value { "alg": "dir",
"enc": "A128GCM" }, describing direct encryption using AES-GCM
with a 128-bit content encryption key. This header is not
transmitted, it is instead implied by the value of the Content-
Encoding header field.
o The JWE Encrypted Key is empty, as stipulated by the direct
encryption algorithm.
o The JWE Initialization Vector ("iv") for each record is set to the
exclusive or of the 96-bit record sequence number, starting at
zero, and a value derived from the input keying material (see
Section 3.3). This value is also not transmitted.
o The final value is the concatenated JWE Ciphertext and the JWE
Authentication Tag, both expressed without URL-safe Base 64
encoding. The "." separator is omitted, since the length of these
fields is known.
Thus, the example in Section 5.4 can be rendered using the JWE
Compact Serialization as:
eyAiYWxnIjogImRpciIsICJlbmMiOiAiQTEyOEdDTSIgfQ..AAAAAAAAAAAAAAAA.
LwTC-fwdKh8de0smD2jfzA.eh1vURhu65M2lxhctbbntA
Where the first line represents the fixed JWE Protected Header, JWE
Encrypted Key, and JWE Initialization Vector, all of which are
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determined algorithmically. The second line contains the encoded
body, split into JWE Ciphertext and JWE Authentication Tag.
Appendix B. Acknowledgements
Mark Nottingham was an original author of this document.
The following people provided valuable input: Richard Barnes, David
Benjamin, Peter Beverloo, Mike Jones, Stephen Farrell, Adam Langley,
John Mattsson, Eric Rescorla, and Jim Schaad.
Author's Address
Martin Thomson
Mozilla
Email: martin.thomson@gmail.com
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