Internet DRAFT - draft-jholland-mboned-ambi
draft-jholland-mboned-ambi
Mboned J. Holland
Internet-Draft K. Rose
Intended status: Standards Track Akamai Technologies, Inc.
Expires: September 10, 2020 March 09, 2020
Asymmetric Manifest Based Integrity
draft-jholland-mboned-ambi-05
Abstract
This document defines Asymmetric Manifest-Based Integrity (AMBI).
AMBI allows each receiver or forwarder of a stream of multicast
packets to check the integrity of the contents of each packet in the
data stream. AMBI operates by passing cryptographically verifiable
hashes of the data packets inside manifest messages, and sending the
manifests over authenticated out-of-band communication channels.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 10, 2020.
Copyright Notice
Copyright (c) 2020 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 Simplified BSD License text as described in Section 4.e of
Holland & Rose Expires September 10, 2020 [Page 1]
Internet-Draft AMBI March 2020
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Comparison with TESLA . . . . . . . . . . . . . . . . . . 4
1.2. Threat Model . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 5
2.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Buffering and Validation Windows . . . . . . . . . . . . 6
2.2.1. Inter-packet Gap . . . . . . . . . . . . . . . . . . 7
2.3. Packet Digests . . . . . . . . . . . . . . . . . . . . . 8
2.3.1. Digest Profile . . . . . . . . . . . . . . . . . . . 8
2.3.2. Pseudoheader . . . . . . . . . . . . . . . . . . . . 11
2.4. Manifests . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4.1. Manifest Layout . . . . . . . . . . . . . . . . . . . 13
2.5. Transitioning to Other Manifest Streams . . . . . . . . . 14
3. Transport Considerations . . . . . . . . . . . . . . . . . . 15
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2. HTTPS . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.3. DTLS . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.4. DTLS + FECFRAME . . . . . . . . . . . . . . . . . . . . . 16
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.1. Tree Diagram . . . . . . . . . . . . . . . . . . . . . . 16
5.2. Module . . . . . . . . . . . . . . . . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
6.1. The YANG Module Names Registry . . . . . . . . . . . . . 19
6.2. Media Type . . . . . . . . . . . . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 19
7.1. Predictable Packets . . . . . . . . . . . . . . . . . . . 19
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1. Normative References . . . . . . . . . . . . . . . . . . 20
9.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
Multicast transport poses security problems that are not easily
addressed by the same security mechanisms used for unicast transport.
The "Introduction" sections of the documents describing TESLA
[RFC4082], and TESLA in SRTP [RFC4383], and TESLA with ALC and NORM
[RFC5776] present excellent overviews of the challenges unique to
multicast authentication, briefly summarized here:
Holland & Rose Expires September 10, 2020 [Page 2]
Internet-Draft AMBI March 2020
o A MAC based on a symmetric shared secret cannot be used because
each packet has multiple receivers that do not trust each other,
and using a symmetric shared secret exposes the same secret to
each receiver.
o Asymmetric per-packet signatures can handle only very low bit-
rates because of the computational overhead.
o An asymmetric signature of a larger message comprising multiple
packets requires reliable receipt of all such packets, something
that cannot be guaranteed in a timely manner even for protocols
that do provide reliable delivery, and the retransmission of which
may anyway exceed the useful lifetime for data formats that can
otherwise tolerate some degree of loss.
Aymmetric Manifest-Based Integrity (AMBI) defines a method for
receivers or middle boxes to cryptographically authenticate and
verify the integrity of a stream of packets, by communicating packet
"manifests" (described in Section 2.4) via an out-of-band
communication channel that provides authentication and verifiable
integrity.
Each manifest contains a message digest (described in Section 2.3)
for each packet in a sequence of packets from the data stream,
hereafter called a "packet digest". The packet digest incorporates a
cryptographic hash of the packet contents and some identifying data
from the packet, according to a defined digest profile for the data
stream.
Each manifest MUST be delivered in a way that provides cryptographic
integrity guarantees of the authenticity of the manifest. For
example, TLS could be used to deliver a stream of manifests over a
unicast data stream from a set of trusted senders to each receiver,
or a protocol that asymmetrically signs each message could be used to
transport authenticated manifests over a multicast channel. Note
that a UDP-based protocol might drop or reorder manifests while still
providing authentication.
Upon successful verification of a manifest and receipt of any subset
of the corresponding data packets, the receiver has proof of the
integrity of the contents of the data packets that are listed in the
manifest.
Authenticating the integrity of the data packets depends on:
o the authenticity of the manifests; and
Holland & Rose Expires September 10, 2020 [Page 3]
Internet-Draft AMBI March 2020
o the authenticity of the digest profile used for construction of
the packet digests; and
o the difficulty of generating a collision for the packet digests
contained in the manifest.
This document defines a YANG [RFC7950] module that augments the DORMS
[I-D.draft-jholland-mboned-dorms-01] YANG module to provide a way to
communicate a digest profile, described in Section 2.3.1, for
construction of the packet digests, described in Section 2.3. When
obtaining the digest profile by using DORMS, the authenticity of the
data stream relies on a trust relationship with the DORMS server,
since that anchors the authenticity of the digest profile for
constructing packet digests.
1.1. Comparison with TESLA
AMBI and TESLA [RFC4082] and [RFC5776] attempt to achieve a similar
goal of authenticating the integrity of streams of multicast packets.
AMBI imposes a higher overhead, as measured in the amount of extra
data required, than TESLA imposes. In exchange, AMBI provides non-
repudiation (which TESLA does not), and relaxes the requirement for
establishing an upper bound on clock synchronization between sender
and receiver.
This tradeoff enables new capabilities for AMBI, relative to TESLA.
In particular, when receiving multicast traffic from an untrusted
transit network, AMBI can be used by a middle box to authenticate
packets from a trusted source before forwarding traffic through the
network, and the receiver also can separately authenticate the
packets it receives.
This use case is not possible with TESLA because the data packets
can't be authenticated until a key is disclosed, so either the
middlebox has to forward data packets without first authenticating
them, so that the receiver has them prior to key disclosure, or the
middlebox has to hold packets until the key is disclosed, at which
point the receiver can no longer establish their authenticity.
The other new capability is that because AMBI provides authentication
information out of band, authentication can be retrofitted into some
pre-existing deployments without changing the protocol of the data
packets, under some restrictions outlined in Section 7. By contrast,
TESLA requires a MAC to be added to each authenticated message.
Holland & Rose Expires September 10, 2020 [Page 4]
Internet-Draft AMBI March 2020
1.2. Threat Model
TBD: Summarize the applicable threat model this protects against. A
diagram plus a cleaned-up version of the on-list explanation here is
probably appropriate: https://mailarchive.ietf.org/arch/msg/mboned/
CG9FLjPwuno3MtvYvgNcD5p69I4/
1.3. 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
[RFC2119] and [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Protocol Operation
2.1. Overview
In order to authenticate a data packet, AMBI receivers need to hold
these three pieces of information at the same time:
o the data packet; and
o an authenticated manifest containing the packet digest for the
data packet; and
o a digest profile defining the transformation from the data packet
to its packet digest.
The manifests are delivered as a stream of manifests over an
authenticated data channel. Manifest contents MUST be authenticated
before they can be used to authenticate data packets.
The manifest stream is composed of an ordered sequence of manifests
that each contain an ordered sequence of packet digests,
corresponding to the original packets as sent from their origin, in
the same order.
Note that a manifest contains potentially many packet digests, and
its size can be tuned to fit within a convenient PDU (Protocol Data
Unit) of the manifest transport stream, so that usually, many packet
digests for the multicast data stream can be delivered per packet of
the manifest transport. The intent is that even with unicast-based
manifest transport, multicast-style efficiencies of scale can still
be realized, with only a relatively small unicast overhead, when
manifests use a unicast transport.
Holland & Rose Expires September 10, 2020 [Page 5]
Internet-Draft AMBI March 2020
2.2. Buffering and Validation Windows
Using different communication channels for the manifest stream and
the data stream introduces a possibility of desynchronization in the
timing of the received data between the different channels, so
receivers hold data packets and packet digests from the manifest
stream in buffers for some duration while awaiting the arrival of
their counterparts.
While holding a data packet, if the corresponding packet digest for
that packet arrives in the manifest stream and can be authenticated,
the data packet is authenticated.
While holding an authenticated packet digest, if the corresponding
data packet arrives with a matching packet digest, the data packet is
authenticated.
Once a data packet is authenticated, the corresponding packet digest
can be discarded and the data packet can be further processed by the
receiving application or forwarded through the receiving network.
Authenticating a data packet consumes one packet digest and prevents
re-learning, with a hold-down time equal to the hold time for packet
digests. A different manifest might provide the same packet digest
with the same packet sequence number, but the digest remains consumed
if it has been used to authenticate a data packet.
If the receiver's hold duration for a data packet expires without
authenticating the packet, the packet SHOULD be dropped as
unauthenticated. If the hold duration of a manifest expires, packet
digests last received in that manifest SHOULD be discarded. (Note
that in some cases, packet digests can be sent redundantly in more
than one manifest. In such cases, the latest received time for an
authenticated packet digest should be used for the expiration time.)
Since packet digests are usually smaller than the data packets, it's
RECOMMENDED that senders generate and send manifests with timing such
that the packet digests in a manifest will typically be received by
subscribed receivers before the data packets corresponding to those
digests are received.
This strategy reduces the buffering requirements at receivers at, the
cost of introducing some buffering of data packets at the sender,
since data packets are generated before their packet digests can be
added to manifests.
The RECOMMENDED default hold times at receivers are:
o 2 seconds for data packets
Holland & Rose Expires September 10, 2020 [Page 6]
Internet-Draft AMBI March 2020
o 10 seconds for packet digests
The sender MAY recommend different values for specific data streams,
in order to tune different data streams for different performance
goals. The YANG model in Section 5 provides a mechanism for senders
to communicate the sender's recommendation for buffering durations,
when using DORMS.
Receivers SHOULD follow the recommendations for hold times provided
by the sender, subject to their capabilities and any administratively
configured limits on buffer sizes at the receiver.
However receivers MAY deviate from the values recommended by the
sender for a variety of reasons. Decreasing the buffering durations
recommended by the server increases the risk of losing packets, but
can be an appropriate tradeoff for specific network conditions and
hardware constraints on some devices.
TBD: should there be any reordering restrictions above and beyond the
timing constraints?
2.2.1. Inter-packet Gap
It's RECOMMENDED that middle boxes forwarding buffered data packets
preserve the inter-packet gap between packets, and that receiving
libraries provide mechanisms to expose the network arrival times of
packets to applications.
The purpose for this recommendation is to preserve the capability of
receivers to use techniques for available bandwidth detection or
network congestion based on observation of packet times. Examples of
such techniques include paced chirping and pathrate.
Note that this recommendation SHOULD NOT prevent the transmission of
an authenticated packet because the prior packet is unauthenticated.
This recommendation only asks implementations to delay the
transmission of an authenticated packet to correspond to the
interpacket gap if an authenticated packet was previously transmitted
and the authentication of the subsequent packet would otherwise burst
the packets more quickly.
This does not prevent the transmission of packets out of order
according to their order of authentication, only the timing of
packets that are transmitted, after authentication, in the same order
they were received.
Holland & Rose Expires September 10, 2020 [Page 7]
Internet-Draft AMBI March 2020
For receiver applications, the time that the original packet was
received from the network SHOULD be made available to the receiving
application.
2.3. Packet Digests
2.3.1. Digest Profile
A packet digest is a message digest for a data packet, built
according to a digest profile defined by the sender.
The digest profile is defined by the sender, and specifies:
1. A cryptographically secure hash algorithm (REQUIRED)
2. A manifest stream identifier
3. Whether to hash the IP payload or the UDP payload. (see
Section 2.3.1.1)
The hash algorithm is applied to a pseudoheader followed by the
packet payload, as determined by the digest profile. The computed
hash value is the packet digest.
TBD: there should also be a way to specify that only packets to a
specific UDP port are applicable. I think this is not quite right
today and probably should be done with a grouping in the yang model,
so that the profile appears either inside a "protocol" container
inside the (S,G) or inside the udp-stream inside the "protocol", but
am not sure. Follow-up on this after the first reference
implementation...
2.3.1.1. Payload Type
2.3.1.1.1. UDP vs. IP payload validation
When the digest profile indicates that UDP payloads are validated,
the IP protocol for the packets MUST be UDP (0x11) and the payload
used for calculating the packet digest includes only the UDP payload,
with length as the number of UDP payload octets, as calculated by
subtracting the size of the UDP header from the UDP payload length.
When the digest profile indicates that IP payloads are validated, the
IP payload of the packet is used, using the outermost IP layer that
contains the (S,G) corresponding to the (S,G) protected by the
manifest. There is no restriction on the IP protocols that can be
authenticated. The length field in the pseudoheader is calculated by
Holland & Rose Expires September 10, 2020 [Page 8]
Internet-Draft AMBI March 2020
subtracting the IP Header Length from the IP length, and is equal to
the number of octets in the payload for the digest calculation.
2.3.1.1.2. Motivation
Full IP payloads often aren't available to receivers without extra
privileges on end user operating systems, so it's useful to provide a
way to authenticate only the UDP payload, which is often the only
portion of the packet available to many receiving applications.
However, for some use cases a full IP payload is appropriate. For
example, when retrofitting some existing protocols, some packets may
be predictable or frequently repeated. Use of an IPSec
Authentication Header [RFC4302] is one way to disambiguate such
packets. Even though the shared secret means the Authentication
Header can't itself be used to authenticate the packet contents, the
sequence number in the Authentication Header can ensure that specific
packets are not repeated at the IP layer, and so it's useful for AMBI
to have the capability to authenticate such packets.
Another example: some services might need to authenticate the UDP
options [I-D.ietf-tsvwg-udp-options]. When using the UDP payload,
the UDP options would not be part of the authenticated payload, but
would be included when using the IP payload type.
Lastly, since (S,G) subscription operates at the IP layer, it's
possible that some non-UDP protocols will need to be authenticated.
2.3.1.2. TBD: Packet contents?
TBD: Determine whether we need to support packet contents in the
packet digest. If so, add to above list in Section 2.3.1:
o A set of bits from the packet contents (potentially empty)
The packet contents are a sequence of bits composed from a sequence
of fixed bit (offset, length) pairs, as specified in xxxxxx. A
useful choice for packet contents is to use sequence numbers in the
application level protocol, such as with RTP [RFC3550], but any
contents from the packet with a fixed bit offset and length can be
used.
Providing variable packet contents in the packet digest increases the
difficulty of attacking the hash by limiting the scope of legitimate
data packets that can be matched when attempting to generate a hash
collision.
Holland & Rose Expires September 10, 2020 [Page 9]
Internet-Draft AMBI March 2020
The basic idea is to put an encoding here so that for example the RTP
sequence number or the sequence number in an Authentication Header
can be provided here in bulk (you give "value starts at bit 80 and is
16 bits long unsigned and increases by 1 per packet for the packets
in the manifest with starting value 10", indicating that the 100
packets in the manifest have values 10-110 in their contents at the
given location. Now those contents are prepended to the packet
digest, and can be verified against the packets, as well as the hash
of the contents).
For packet streams without a sequence number, we can instead
incorporate a few high-entropy bits from the packet contents and NOT
provide the value as a sequence number, but rather incorporate it in
the digest values themselves. (Is this useful?)
Before defining this, I want to calculate how much overhead it buys
us- how much can we truncate a good hash algorithm if we use this to
add collision resistance? Might not be worthwhile, it's a
significant increase in complexity. -jake 2019-08-31
If we need it, tentative addition to yang for the data profile looks
like:
list packet-contents {
key offset;
description "contents from the packet for the packet
digest";
leaf offset {
type uint16;
mandatory true;
description "offset of the contents, in number of bits";
}
leaf length {
type uint16;
mandatory true;
description "length of the contents, in number of bits";
}
leaf manifest-delivery {
type enumeration {
enum sequence;
enum digest;
}
mandatory true;
description "the way these content bits are delivered in
the manifest";
}
}
Holland & Rose Expires September 10, 2020 [Page 10]
Internet-Draft AMBI March 2020
The manifest-delivery would indicate whether the bits are a sequence
number (in which case a section for a manifest with a start+step
would be added ahead of the digests), or digest (indicating the bits
appear inside each digest, ahead of the hash), and they would prepend
in order to the packet digest, with sequence number bits inserted at
the right bit location for the digest, based on earlier-appearing
values, if any.
2.3.2. Pseudoheader
When calculating the hash for the packet digest, the hash algorithm
is applied to a pseudoheader followed by the payload from the packet.
The complete sequence of octets used to calculate the hash is
structured as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address (32 bits IPv4/128 bits IPv6) |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address (32 bits IPv4/128 bits IPv6) |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Zeroes | Protocol | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Destination Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Manifest Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Data |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2.3.2.1. Source Address
The IPv4 or IPv6 source address of the packet.
2.3.2.2. Destination Address
The IPv4 or IPv6 destination address of the packet.
2.3.2.3. Zeroes
All bits set to 0.
Holland & Rose Expires September 10, 2020 [Page 11]
Internet-Draft AMBI March 2020
2.3.2.4. Protocol
The IP Protocol field from IPv4, or the Next Header field for IPv6.
When UDP payload is indicated, this value MUST be UDP (0x11).
2.3.2.5. Length
The length in octets of the Payload Data field, expressed as an
unsigned 16-bit integer.
2.3.2.6. Source Port
The source port of the packet. Zeroes if using a protocol that does
not use source ports.
2.3.2.7. Destination Port
The destination port of the packet. Zeroes if using a protocol that
does not use destination ports.
TBD: there's something I hate about the source and destination ports.
Maybe it should only be active in UDP-payload mode, instead of zeroes
when not UDP? But I suspect there's a better approach than UDP-or-
not, so it's this way for now, with hopes of finding something better
in the next version.
2.3.2.8. Manifest Identifier
The 32-bit identifier for the manifest stream.
2.3.2.9. Payload Data
The payload data includes either the IP payload or the UDP payload,
as indicated by the digest profile.
The payload type is configurable because when sending UDP, some
legacy networks may strip the UDP option space, and it's necessary to
provide a manifest stream capable of authentication that can
interoperate with these networks. However, for non-UDP traffic or in
order to authenticate the UDP options, some use cases may require
support for authenticating the full IP payload.
2.4. Manifests
Holland & Rose Expires September 10, 2020 [Page 12]
Internet-Draft AMBI March 2020
2.4.1. Manifest Layout
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Manifest Stream Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Manifest sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| First packet sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Refresh Deadline | Packet Digest Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... Packet Content Expansions ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... Packet Digests ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2.4.1.1. Manifest Stream Identifier
A 32-bit unsigned integer chosen by the sender.
2.4.1.2. Manifest Sequence Number
A monotonically increasing 32-bit unsigned integer. Each manifest
sent by the sender increases this value by 1. On overflow it wraps
to 0.
It's RECOMMENDED to expire the manifest stream and start a new stream
for the data packets before a sequence number wrap is necessary.
2.4.1.3. First Packet Sequence Number
A monotonically increasing 32-bit unsigned integer. Each packet in
the data stream increases this value by 1.
It's RECOMMENDED to expire the manifest stream and start a new stream
for the data packets before a sequence number wrap is necessary.
Note: for redundancy, especially if using a manifest stream with
unreliable transport, successive manifests MAY provide duplicates of
the same packet digest with the same packet sequence number, using
overapping sets of packet sequence numbers. When received, these
reset the hold timer for the listed packet digests.
Holland & Rose Expires September 10, 2020 [Page 13]
Internet-Draft AMBI March 2020
2.4.1.4. Refresh Deadline
A 16-bit unsigned integer number of seconds.
A zero value means the current digest profile for the current
manifest stream is stable.
A nonzero value means that the authentication is transitioning to a
new manifest stream, and the set of digest profiles SHOULD be
refreshed by receivers that might stay joined longer than this
duration, and a different manifest stream SHOULD be selected, before
this many seconds have elapsed, in order to avoid a disruption. See
Section 2.5.
2.4.1.5. Packet Digest Count
The count of packet digests in the manifest.
2.4.1.6. Packet Digests
Packet digests appended one after the other, aligned to 8-bit
boundaries with zero padding (if the bit length of the digests are
not multiples of 8 bits).
2.5. Transitioning to Other Manifest Streams
It's possible for multiple manifest streams authenticating the same
data stream to be active at the same time. The different manifest
streams can have different hash algorithms, manifest ids, and current
packet sequence numbers for the same data stream. These result in
different sets of packet digests for the same data packets, one
digest per packet per digest profile.
It's necessary sometimes to transition gracefully from one manifest
stream to another. The Refresh Deadline field from the manifest is
used to signal to receivers the need to transition.
When a receiver gets a nonzero refresh deadline in a manifest the
sender SHOULD have an alternate manifest stream ready and available,
and the receiver SHOULD learn the alternate manifest stream, join the
new one, and leave the old one before the number of seconds given in
the refresh deadline. After the refresh deadline has expired, a
manifest stream MAY end.
The receivers SHOULD use a random value between now and one half the
number of seconds in the deadline field, to spread the spike of load
on the DORMS server during a large multicast event.
Holland & Rose Expires September 10, 2020 [Page 14]
Internet-Draft AMBI March 2020
3. Transport Considerations
3.1. Overview
AMBI manifests MUST be authenticated, but any transport protocol
providing authentication can be used. This section discusses several
viable options for the use of an authenticating transport, and some
associated design considerations.
TBD: extend the 'manifest-transport' in the YANG model to make an
extensible mechanism to advertise different transport options for
receiving manifest streams.
TBD: add ALTA to the list when and if it gets further along
[I-D.draft-krose-mboned-alta-01]. Sending an authenticatable
multicast stream (instead of the below unicast-based proposals) is a
worthwhile goal, else a 1% unicast authentication overhead becomes a
new unicast limit to the scalability.
3.2. HTTPS
This document defines a new media type 'application/ambi' for use
with HTTPS.
An HTTPS stream carrying the 'application/ambi' media type is
composed of a sequence of binary AMBI manifests. It is RECOMMENDED
to use Chunked encoding.
Complete packet Digests from partially received manifests MAY be used
by the receiver for authentication, even if the full manifest is not
yet delivered.
3.3. DTLS
TBD: DTLS [RFC6347] can provide authentication for datagrams, so if
manifests can be constructed to fit within datagrams, it is an
appropriate choice. (IPSec is similar-worth adding as an option?).
This option provides no native redundancy or retransmission, but
packet digests can be repeated in different manifests to provide some
resilience to loss. Lost manifests that result in the loss of blocks
of packet digests can be expensive, since they would make received
data packets unauthenticatable. TBD: should we therefore not support
this case?
Holland & Rose Expires September 10, 2020 [Page 15]
Internet-Draft AMBI March 2020
3.4. DTLS + FECFRAME
DTLS for manifests that do not fit into single-packet payloads can
still be delivered by using FECFRAME [RFC6363], particularly Reed-
Solomon [RFC6865] or possibly Raptor [RFC6681]. This has some
advantages compared to HTTPS because of the absence of HOL-blocking,
while providing for tunable redundancy. This has some advantages
relative to DTLS because of overhead reduction and non-integer
redundancy tunability (e.g. 1.5 becomes a viable redundancy factor).
TBD: define this method, possibly in another RFC.
4. Examples
TBD: walk through some examples as soon as we have a build running.
Likely to need some touching up.
5. YANG Module
5.1. Tree Diagram
module: ietf-ambi
augment /dorms:metadata/dorms:sender/dorms:group/dorms:udp-stream:
+--rw manifest-stream* [id]
+--rw id uint32
+--rw manifest-transport* inet:uri
+--rw hash-algorithm ct:asymmetric-key-algorithm-t
+--rw payload-type enumeration
+--rw data-hold-time-ms? uint32
+--rw digest-hold-time-ms? uint32
5.2. Module
<CODE BEGINS> file ietf-ambi@2020-03-09.yang
module ietf-ambi {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-ambi";
prefix "ambi";
import ietf-dorms {
prefix "dorms";
reference "I-D.jholland-mboned-dorms";
}
import ietf-inet-types {
prefix "inet";
Holland & Rose Expires September 10, 2020 [Page 16]
Internet-Draft AMBI March 2020
reference "RFC6991 Section 4";
}
import ietf-crypto-types {
prefix "ct";
reference "draft-ietf-netconf-crypto-types";
}
organization "IETF";
contact
"Author: Jake Holland
<mailto:jholland@akamai.com>
";
description
"Copyright (c) 2019 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject to
the license terms contained in, the Simplified BSD License set
forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX
(https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
for full legal notices.
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 (RFC 2119) (RFC 8174) when, and only when,
they appear in all capitals, as shown here.
This module contains the definition for the AMBI data types.
It provides metadata for authenticating SSM channels as an
augmentation to DORMS.";
revision 2019-08-25 {
description "Initial revision as an extension.";
reference
"";
}
augment
"/dorms:metadata/dorms:sender/dorms:group/dorms:udp-stream" {
Holland & Rose Expires September 10, 2020 [Page 17]
Internet-Draft AMBI March 2020
description "Definition of the manifest stream providing
integrity info for the data stream";
list manifest-stream {
key id;
description "Definition of a manifest stream.";
leaf id {
type uint32;
mandatory true;
description "The Manifest ID referenced in a manifest.";
}
leaf-list manifest-transport {
type inet:uri;
description "A URI that provides a location for the
manifest stream";
}
leaf hash-algorithm {
type ct:asymmetric-key-algorithm-t;
mandatory true;
description
"The hash algorithm for the packet hashes within
manifests in this stream.";
}
leaf payload-type {
type enumeration {
enum udp {
description "The hash includes only the UDP
payload.";
}
enum ip {
description "The hash includes the full IP
payload.";
}
}
mandatory true;
description "The contents of the payload for the
digest profile";
}
leaf data-hold-time-ms {
type uint32;
default 2000;
description "The number of milliseconds to hold data
packets waiting for a corresponding digest before
discarding";
}
leaf digest-hold-time-ms {
type uint32;
default 10000;
Holland & Rose Expires September 10, 2020 [Page 18]
Internet-Draft AMBI March 2020
description "The number of milliseconds to hold packet
digests waiting for a corresponding data packet
before discarding";
}
}
}
}
<CODE ENDS>
6. IANA Considerations
6.1. The YANG Module Names Registry
This document adds one YANG module to the "YANG Module Names"
registry maintained at <https://www.iana.org/assignments/yang-
parameters>. The following registrations are made, per the format in
Section 14 of [RFC6020]:
name: ietf-ambi
namespace: urn:ietf:params:xml:ns:yang:ietf-ambi
prefix: ambi
reference: I-D.draft-jholland-mboned-ambi
6.2. Media Type
TBD: Register 'application/ambi' according to advice from:
https://www.iana.org/form/media-types
TBD: check guidelines in https://tools.ietf.org/html/rfc5226
7. Security Considerations
7.1. Predictable Packets
Protocols that have predictable packets run the risk of offline
attacks for hash collisions against those packets. When
authenticating a protocol that might have predictable packets, it's
RECOMMENDED to use a hash function secure against such attacks or to
add content to the packets to make them unpredictable, such as an
Authentication Header ([RFC4302]), or the addition of an ignored
field with random content to the packet payload.
TBD: explain attack from generating malicious packets and then
looking for collisions, as opposed to having to generate a collision
on packet contents that include a sequence number and then hitting a
match (especially expand on this if we do add Section 2.3.1.2).
Holland & Rose Expires September 10, 2020 [Page 19]
Internet-Draft AMBI March 2020
TBD: follow the rest of the guidelines: https://tools.ietf.org/html/
rfc3552
8. Acknowledgements
Many thanks to Daniel Franke, Eric Rescorla, Christian Worm
Mortensen, Max Franke, and Albert Manfredi for their very helpful
comments and suggestions.
9. References
9.1. Normative References
[I-D.draft-jholland-mboned-dorms-01]
Holland, J., "Discovery Of Restconf Metadata for Source-
specific multicast", draft-jholland-mboned-dorms-01 (work
in progress), September 2019.
[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>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6363] Watson, M., Begen, A., and V. Roca, "Forward Error
Correction (FEC) Framework", RFC 6363,
DOI 10.17487/RFC6363, October 2011,
<https://www.rfc-editor.org/info/rfc6363>.
[RFC6681] Watson, M., Stockhammer, T., and M. Luby, "Raptor Forward
Error Correction (FEC) Schemes for FECFRAME", RFC 6681,
DOI 10.17487/RFC6681, August 2012,
<https://www.rfc-editor.org/info/rfc6681>.
[RFC6865] Roca, V., Cunche, M., Lacan, J., Bouabdallah, A., and K.
Matsuzono, "Simple Reed-Solomon Forward Error Correction
(FEC) Scheme for FECFRAME", RFC 6865,
DOI 10.17487/RFC6865, February 2013,
<https://www.rfc-editor.org/info/rfc6865>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
Holland & Rose Expires September 10, 2020 [Page 20]
Internet-Draft AMBI March 2020
[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>.
9.2. Informative References
[I-D.draft-krose-mboned-alta-01]
Rose, K. and J. Holland, "Asymmetric Loss-Tolerant
Authentication", draft-krose-mboned-alta-01 (work in
progress), July 2019.
[I-D.ietf-tsvwg-udp-options]
Touch, J., "Transport Options for UDP", draft-ietf-tsvwg-
udp-options-08 (work in progress), September 2019.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <https://www.rfc-editor.org/info/rfc3550>.
[RFC4082] Perrig, A., Song, D., Canetti, R., Tygar, J., and B.
Briscoe, "Timed Efficient Stream Loss-Tolerant
Authentication (TESLA): Multicast Source Authentication
Transform Introduction", RFC 4082, DOI 10.17487/RFC4082,
June 2005, <https://www.rfc-editor.org/info/rfc4082>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>.
[RFC4383] Baugher, M. and E. Carrara, "The Use of Timed Efficient
Stream Loss-Tolerant Authentication (TESLA) in the Secure
Real-time Transport Protocol (SRTP)", RFC 4383,
DOI 10.17487/RFC4383, February 2006,
<https://www.rfc-editor.org/info/rfc4383>.
[RFC5776] Roca, V., Francillon, A., and S. Faurite, "Use of Timed
Efficient Stream Loss-Tolerant Authentication (TESLA) in
the Asynchronous Layered Coding (ALC) and NACK-Oriented
Reliable Multicast (NORM) Protocols", RFC 5776,
DOI 10.17487/RFC5776, April 2010,
<https://www.rfc-editor.org/info/rfc5776>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
Holland & Rose Expires September 10, 2020 [Page 21]
Internet-Draft AMBI March 2020
Authors' Addresses
Jake Holland
Akamai Technologies, Inc.
150 Broadway
Cambridge, MA 02144
United States of America
Email: jakeholland.net@gmail.com
Kyle Rose
Akamai Technologies, Inc.
150 Broadway
Cambridge, MA 02144
United States of America
Email: krose@krose.org
Holland & Rose Expires September 10, 2020 [Page 22]
