Internet DRAFT - draft-ietf-sframe-enc
draft-ietf-sframe-enc
Network Working Group E. Omara
Internet-Draft Apple
Intended status: Standards Track J. Uberti
Expires: 14 September 2023 Google
S. Murillo
CoSMo Software
R. L. Barnes, Ed.
Cisco
Y. Fablet
Apple
13 March 2023
Secure Frame (SFrame)
draft-ietf-sframe-enc-01
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.
The proposed 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.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://sframe-
wg.github.io/sframe/draft-ietf-sframe-enc.html. Status information
for this document may be found at https://datatracker.ietf.org/doc/
draft-ietf-sframe-enc/.
Discussion of this document takes place on the Secure Media Frames
Working Group mailing list (mailto:sframe@ietf.org), which is
archived at https://mailarchive.ietf.org/arch/browse/sframe/.
Subscribe at https://www.ietf.org/mailman/listinfo/sframe/.
Source for this draft and an issue tracker can be found at
https://github.com/sframe-wg/sframe.
Omara, et al. Expires 14 September 2023 [Page 1]
Internet-Draft SFrame March 2023
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 14 September 2023.
Copyright Notice
Copyright (c) 2023 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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. SFrame . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Application Context . . . . . . . . . . . . . . . . . . . 6
4.2. SFrame Ciphertext . . . . . . . . . . . . . . . . . . . . 7
4.3. SFrame Header . . . . . . . . . . . . . . . . . . . . . . 8
4.4. Encryption Schema . . . . . . . . . . . . . . . . . . . . 10
4.4.1. Key Selection . . . . . . . . . . . . . . . . . . . . 10
4.4.2. Key Derivation . . . . . . . . . . . . . . . . . . . 11
4.4.3. Encryption . . . . . . . . . . . . . . . . . . . . . 11
4.4.4. Decryption . . . . . . . . . . . . . . . . . . . . . 14
4.4.5. Duplicate Frames . . . . . . . . . . . . . . . . . . 14
4.5. Ciphersuites . . . . . . . . . . . . . . . . . . . . . . 14
4.5.1. AES-CTR with SHA2 . . . . . . . . . . . . . . . . . . 15
Omara, et al. Expires 14 September 2023 [Page 2]
Internet-Draft SFrame March 2023
5. Key Management . . . . . . . . . . . . . . . . . . . . . . . 16
5.1. Sender Keys . . . . . . . . . . . . . . . . . . . . . . . 17
5.2. MLS . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6. Media Considerations . . . . . . . . . . . . . . . . . . . . 19
6.1. SFU . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6.1.1. LastN and RTP stream reuse . . . . . . . . . . . . . 19
6.1.2. Simulcast . . . . . . . . . . . . . . . . . . . . . . 20
6.1.3. SVC . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.2. Video Key Frames . . . . . . . . . . . . . . . . . . . . 20
6.3. Partial Decoding . . . . . . . . . . . . . . . . . . . . 21
7. Security Considerations . . . . . . . . . . . . . . . . . . . 21
7.1. No Per-Sender Authentication . . . . . . . . . . . . . . 21
7.2. Key Management . . . . . . . . . . . . . . . . . . . . . 21
7.3. Authentication tag length . . . . . . . . . . . . . . . . 21
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
9.1. Normative References . . . . . . . . . . . . . . . . . . 21
9.2. Informative References . . . . . . . . . . . . . . . . . 22
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 23
Appendix B. Overhead . . . . . . . . . . . . . . . . . . . . . . 23
B.1. Audio . . . . . . . . . . . . . . . . . . . . . . . . . . 23
B.2. Video . . . . . . . . . . . . . . . . . . . . . . . . . . 24
B.3. SFrame vs PERC-lite . . . . . . . . . . . . . . . . . . . 25
B.3.1. Audio . . . . . . . . . . . . . . . . . . . . . . . . 25
B.3.2. Video . . . . . . . . . . . . . . . . . . . . . . . . 25
Appendix C. Test Vectors . . . . . . . . . . . . . . . . . . . . 26
C.1. AES_CTR_128_HMAC_SHA256_4 . . . . . . . . . . . . . . . . 26
C.2. AES_CTR_128_HMAC_SHA256_8 . . . . . . . . . . . . . . . . 28
C.3. AES_GCM_128_SHA256 . . . . . . . . . . . . . . . . . . . 30
C.4. AES_GCM_256_SHA512 . . . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction
Modern multi-party video call systems use Selective Forwarding Unit
(SFU) servers to efficiently route RTP 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, allowing for the media
to be "end-to-end" encrypted 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 encryptions and authentication are required:
1. Hop-by-hop (HBH) encryption of media, metadata, and feedback
messages between the the endpoints and SFU
Omara, et al. Expires 14 September 2023 [Page 3]
Internet-Draft SFrame March 2023
2. End-to-end (E2E) encryption 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 end-to-end encryption mechanism 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 payloads sent over SRTP
+---+-+-+-------+-+-------------+-------------------------------+<-+
|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 1: SRTP packet with SFrame-protected payload
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.
SFU: Selective Forwarding Unit (AKA RTP Switch)
Omara, et al. Expires 14 September 2023 [Page 4]
Internet-Draft SFrame March 2023
IV: Initialization Vector
MAC: Message Authentication Code
E2EE: End to End Encryption
HBH: Hop By Hop
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 an 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. Independence from the underlying transport, including use in non-
RTP transports, e.g., WebTransport.
5. When used with RTP and its associated error resilience
mechanisms, i.e., RTX and 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
end-to-end encryption, is simple to implement, has no dependencies on
RTP, and minimizes encryption bandwidth overhead. Because SFrame can
encrypt a full frame, rather than individual packets, bandwidth
overhead can reduced by adding encryption overhead only once per
media frame, instead of once per packet.
Omara, et al. Expires 14 September 2023 [Page 5]
Internet-Draft SFrame March 2023
4.1. Application Context
SFrame is a general encryption framing, which is typically applied in
one of two ways: Either to encrypt whole media frames (per-frame) or
individual media payloads (per-packet). 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.
For example, Figure 2 shows a typical media stack that takes media in
from some source, encodes it into frames, divides those frames into
media payloads, and then sends those payloads in SRTP packets.
Arrows indicate the points where SFrame protection would be
integrated into this media stack, when applied per-frame or per-
packet.
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 precise efficiency and
complexity trade-offs will depend on the environment in which SFrame
is being integrated.
Omara, et al. Expires 14 September 2023 [Page 6]
Internet-Draft SFrame March 2023
+--------------------------------------------------------+
| |
| +----------+ +-------------+ +-----------+ |
.-. | | | | | | SRTP | |
| | | | Encode |----->| Packetize |----->| Encrypt |-----------+
'+' | | | ^ | | ^ | | | |
/|\ | +----------+ | +-----+-------+ | +-----------+ | |
/ + \ | | ^ | ^ | |
/ \ | SFrame | SFrame | | |
/ \ | Protect | Protect | | |
Alice | (per-frame) | (per-packet) | | |
+--------------------------|--------------------|--------+ |
| | v
| | +-----+------+
E2E Key | HBH Key | | Media |
Management | Management | | Server |
| | +-----+------+
| | |
+--------------------------|--------------------|--------+ |
.-. | SFrame | SFrame | | |
| | | Unprotect | Unprotect | | |
'+' | (per-frame) | (per-packet) | | |
/|\ | | V | V | |
/ + \ | +----------+ | +-----+-------+ | +-----------+ | |
/ \ | | | V | | V | SRTP | | |
/ \ | | Decode |<-----| Depacketize |<-----| Decrypt |<----------+
Bob | | | | | | | |
| +----------+ +-------------+ +-----------+ |
| |
+--------------------------------------------------------+
Figure 2
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 IVs.
4.2. SFrame Ciphertext
An SFrame ciphertext comprises an SFrame header followed by the
output of an AEAD encryption of the plaintext [RFC5116], with the
header provided as additional authenticated data (AAD).
Omara, et al. Expires 14 September 2023 [Page 7]
Internet-Draft SFrame March 2023
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.
+-+---+-+----+------------------------------------------+^+
|S|LEN|X|KID | Frame Counter | |
+^+-+---+-+----+------------------------------------------+ |
| | | |
| | | |
| | | |
| | | |
| | Encrypted Data | |
| | | |
| | | |
| | | |
| | | |
+>+-------------------------------------------------------+<+
| | Authentication Tag | |
| +-------------------------------------------------------+ |
| |
| |
+---- Encrypted Portion Authenticated Portion ---+
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.
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 IV for the
encryption
Applications MUST ensure that each (KID, CTR) combination is used for
exactly one encryption operation. 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. Note that in addition to its
simplicity, this scheme minimizes overhead by keeping CTR values as
small as possible.
Omara, et al. Expires 14 September 2023 [Page 8]
Internet-Draft SFrame March 2023
Both the counter and the key id are encoded as integers in network
(big-endian) byte order, in a variable length format to decrease the
overhead. The length of each field is up to 8 bytes and is
represented in 3 bits in the SFrame header: 000 represents a length
of 1, 001 a length of 2, etc.
The first byte in the SFrame header has a fixed format and contains
the header metadata:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|R| LEN |X| K |
+-+-+-+-+-+-+-+-+
Figure 3: SFrame header metadata
Reserved (R, 1 bit): This field MUST be set to zero on sending, and
MUST be ignored by receivers.
Counter Length (LEN, 3 bits): This field indicates the length of the
CTR field in bytes, minus one (the range of possible values is
thus 1-8).
Extended Key Id Flag (X, 1 bit): Indicates if the key field contains
the key id or the key length.
Key or Key Length (K, 3 bits): This field contains the key id (KID)
if the X flag is set to 0, or the key length (KLEN) if set to 1.
If X flag is 0, then the KID is in the range of 0-7 and the counter
(CTR) is found in the next LEN bytes:
0 1 2 3 4 5 6 7
+-+-----+-+-----+---------------------------------+
|R|LEN |0| KID | CTR... (length=LEN) |
+-+-----+-+-----+---------------------------------+
Figure 4: SFrame header with short KID
If X flag is 1 then KLEN is the length of the key (KID) in bytes,
minus one (the range of possible lengths is thus 1-8). The KID is
encoded in the KLEN bytes following the metadata byte, and the
counter (CTR) is encoded in the next LEN bytes:
0 1 2 3 4 5 6 7
+-+-----+-+-----+---------------------------+---------------------------+
|R|LEN |1|KLEN | KID... (length=KLEN) | CTR... (length=LEN) |
+-+-----+-+-----+---------------------------+---------------------------+
Omara, et al. Expires 14 September 2023 [Page 9]
Internet-Draft SFrame March 2023
4.4. Encryption Schema
SFrame encryption uses an AEAD encryption algorithm and hash function
defined by the ciphersuite in use (see Section 4.5). We will refer
to the following aspects of the AEAD 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 of a key for the encryption algorithm, in bytes
* AEAD.Nn - The size of a nonce for the encryption algorithm, in
bytes
* AEAD.Nt - The overhead of the encryption algorithm, in bytes
(typically the size of a "tag" that is added to the plaintext)
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 key should be used
for a given KID. The process for provisioning keys 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 counter value CTR to be used when
encrypting (initially 0).
When encrypting a plaintext, the application specifies which KID is
to be used, and the counter 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.
Omara, et al. Expires 14 September 2023 [Page 10]
Internet-Draft SFrame March 2023
A given 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 SHOULD mark each 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 encrytion and decryption use a key and salt derived from the
base_key associated to a KID. Given a base_key value, the key and
salt are derived using HKDF [RFC5869] as follows:
sframe_secret = HKDF-Extract(base_key, 'SFrame10')
sframe_key = HKDF-Expand(sframe_secret, 'key', AEAD.Nk)
sframe_salt = HKDF-Expand(sframe_secret, 'salt', AEAD.Nn)
The hash function used for HKDF is determined by the ciphersuite in
use.
4.4.3. Encryption
SFrame encryption uses the AEAD encryption algorithm for the
ciphersuite in use. The key for the encryption is the sframe_key and
the nonce is formed by XORing the sframe_salt with the current
counter, encoded 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.
Omara, et al. Expires 14 September 2023 [Page 11]
Internet-Draft SFrame March 2023
def encrypt(S, CTR, KID, metadata, plaintext):
sframe_key, sframe_salt = key_store[KID]
ctr = encode_big_endian(CTR, AEAD.Nn)
nonce = xor(sframe_salt, CTR)
header = encode_sframe_header(CTR, KID)
aad = header + metadata
ciphertext = AEAD.Encrypt(sframe_key, nonce, aad, plaintext)
return header + ciphertext
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
visibile to the SFU (e.g., an RTP header extension).
The encrypted payload is then passed to a generic RTP packetized to
construct the RTP packets and encrypt it using SRTP keys for the HBH
encryption to the media server.
Omara, et al. Expires 14 September 2023 [Page 12]
Internet-Draft SFrame March 2023
+----------------+ +---------------+
| frame metadata | | |
+-------+--------+ | |
| | frame |
| | |
| | |
| +-------+-------+
| |
header ----+------------------>| AAD
+-----+ |
| S | |
+-----+ |
| KID +--+--> sframe_key ----->| Key
| | | |
| | +--> sframe_salt --+ |
+-----+ | |
| CTR +---------------------+->| Nonce
| | |
| | |
+-----+ |
| AEAD.Encrypt
| |
| V
| +-------+-------+
| | |
| | |
| | encrypted |
| | frame |
| | |
| | |
| +-------+-------+
| |
| generic RTP packetize
| |
| |
| +----------------------+--------.....--------+
| | | |
V V V V
+---------------+ +---------------+ +---------------+
| SFrame header | | | | |
+---------------+ | | | |
| | | payload 2/N | ... | payload N/N |
| payload 1/N | | | | |
| | | | | |
+---------------+ +---------------+ +---------------+
Figure 5: Encryption flow with per-frame encryption
Omara, et al. Expires 14 September 2023 [Page 13]
Internet-Draft SFrame March 2023
4.4.4. Decryption
Before decrypting, a client needs to assemble a full SFrame
ciphertext. When SFrame is applied per-packet, this is done by
extracting the payload of a decrypted SRTP packet. When SFrame is
applied per-frame, the receiving client buffers all packets that
belongs to the same frame using the frame beginning and ending marks
in the generic RTP frame header extension. Once all packets are
available and in order, the receiver forms an SFrame ciphertext by
concatenating their payloads, then 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.
def decrypt(metadata, sframe):
CTR, KID, ciphertext = parse_ciphertext(sframe)
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.
4.4.5. Duplicate Frames
Unlike messaging application, in video calls, receiving a duplicate
frame doesn't necessary mean the client is under a replay attack,
there are other reasons that might cause this, for example the sender
might just be sending them in case of packet loss. SFrame decryptors
use the highest received frame counter to protect against this. It
allows only older frame pithing a short interval to support out of
order delivery.
4.5. Ciphersuites
Each SFrame session uses a single ciphersuite that specifies the
following primitives:
* A hash function used for key derivation
Omara, et al. Expires 14 September 2023 [Page 14]
Internet-Draft SFrame March 2023
* An AEAD encryption algorithm [RFC5116] used for frame encryption,
optionally with a truncated authentication tag
This document defines the following ciphersuites:
+========+============================+==+==+====+====+===========+
| Value | Name |Nh|Nk| Nn | Nt | Reference |
+========+============================+==+==+====+====+===========+
| 0x0001 | AES_CTR_128_HMAC_SHA256_80 |32|16| 12 | 10 | RFC XXXX |
+--------+----------------------------+--+--+----+----+-----------+
| 0x0002 | AES_CTR_128_HMAC_SHA256_64 |32|16| 12 | 8 | RFC XXXX |
+--------+----------------------------+--+--+----+----+-----------+
| 0x0003 | AES_CTR_128_HMAC_SHA256_32 |32|16| 12 | 4 | RFC XXXX |
+--------+----------------------------+--+--+----+----+-----------+
| 0x0004 | AES_GCM_128_SHA256_128 |32|16| 12 | 16 | RFC XXXX |
+--------+----------------------------+--+--+----+----+-----------+
| 0x0005 | AES_GCM_256_SHA512_128 |64|32| 12 | 16 | RFC XXXX |
+--------+----------------------------+--+--+----+----+-----------+
Table 1
In the suite names, the length of the authentication tag is indicated
by the last value: "_128" indicates a hundred-twenty-eight-bit tag,
"_80" indicates a eighty-bit tag, "_64" indicates a sixty-four-bit
tag and "_32" indicates a thirty-two-bit tag.
In a session that uses multiple media streams, different ciphersuites
might be configured for different media streams. For example, in
order to conserve bandwidth, a session might use a ciphersuite with
eighty-bit tags for video frames and another ciphersuite with thirty-
two-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 using HKDF. The subkeys
are derived as follows, where Nk represents the key size for the AES
block cipher in use and Nh represents the output size of the hash
function:
Omara, et al. Expires 14 September 2023 [Page 15]
Internet-Draft SFrame March 2023
def derive_subkeys(sframe_key):
aead_secret = HKDF-Extract(sframe_key, 'SFrame10 AES CTR AEAD')
enc_key = HKDF-Expand(aead_secret, 'enc', Nk)
auth_key = HKDF-Expand(aead_secret, 'auth', Nh)
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 tag_len fixed by the
ciphersuite.
def compute_tag(auth_key, nonce, aad, ct):
aad_len = encode_big_endian(len(aad), 8)
ct_len = encode_big_endian(len(ct), 8)
auth_data = aad_len + ct_len + nonce + aad + ct
tag = HMAC(auth_key, auth_data)
return truncate(tag, tag_len)
def AEAD.Encrypt(key, nonce, aad, pt):
enc_key, auth_key = derive_subkeys(key)
ct = AES-CTR.Encrypt(enc_key, nonce, 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")
return AES-CTR.Decrypt(enc_key, nonce, 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
Omara, et al. Expires 14 September 2023 [Page 16]
Internet-Draft SFrame March 2023
It is up to the application to define a rotation schedule for keys.
For example, one application might have an ephemeral group for every
call and keep rotating key when end points joins 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.
5.1. Sender Keys
If the participants in a call have a pre-existing E2E-secure channel,
they can use it to distribute SFrame keys. Each client participating
in a call generates a fresh encryption key. 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, for example the RTP
SSRC. SFrame KID values are then used to distinguish generations of
the sender's key. At the beginning of a call, each sender encrypts
with KID=0. Thereafter, the sender can ratchet their key forward for
forward secrecy:
sender_key[i+1] = HKDF-Expand(
HKDF-Extract(sender_key[i], 'SFrame10 ratchet'),
'', AEAD.Nk)
The sender signals such an update by incrementing their KID value. 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 mid-call, 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.
5.2. MLS
The Messaging Layer Security (MLS) protocol provides group
authenticated key exchange [I-D.ietf-mls-architecture]
[I-D.ietf-mls-protocol]. In principle, it could be used to
instantiate the sender key scheme above, but it can also be used more
efficiently directly.
Omara, et al. Expires 14 September 2023 [Page 17]
Internet-Draft SFrame March 2023
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 know as an "epoch", and each member of the group is assigned an
"index" that is constant for the time they are in the group.
In SFrame, we derive per-sender base_key values from the group secret
for an epoch, and use the KID field to signal the epoch and sender
index. First, we use the MLS exporter to compute a shared SFrame
secret for the epoch.
sframe_epoch_secret = MLS-Exporter("SFrame 10 MLS", "", AEAD.Nk)
sender_base_key[index] = HKDF-Expand(sframe_epoch_secret,
encode_big_endian(index, 4), AEAD.Nk)
For compactness, do not send the whole epoch number. Instead, we
send only its low-order E bits. Note that E effectively defines a
re-ordering window, since no more than 2^E epoch can be active at a
given time. Receivers MUST be prepared for the epoch counter to roll
over, removing an old epoch when a new epoch with the same E lower
bits is introduced. (Sender indices cannot be similarly compressed.)
KID = (sender_index << E) + (epoch % (1 << E))
Once an SFrame stack has been provisioned with the
sframe_epoch_secret for an epoch, it can compute the required KIDs
and sender_base_key values on demand, as it needs to encrypt/decrypt
for a given member.
Omara, et al. Expires 14 September 2023 [Page 18]
Internet-Draft SFrame March 2023
...
|
Epoch 17 +--+-- index=33 --> KID = 0x211
| |
| +-- index=51 --> KID = 0x331
|
|
Epoch 16 +--+-- index=2 ---> KID = 0x20
|
|
Epoch 15 +--+-- index=3 ---> KID = 0x3f
| |
| +-- index=5 ---> KID = 0x5f
|
|
Epoch 14 +--+-- index=3 ---> KID = 0x3e
| |
| +-- index=7 ---> KID = 0x7e
| |
| +-- index=20 --> KID = 0x14e
|
...
6. Media Considerations
6.1. SFU
Selective Forwarding Units (SFUs) as described in Section 3.7 of
[RFC7667] receives the RTP streams from each participant and selects
which ones should be forwarded to each of the other participants.
There are several approaches about how to do this stream selection
but in general, in order to do so, the SFU needs to access metadata
associated to each frame and modify the RTP information of the
incoming packets when they are transmitted to the received
participants.
This section describes how this normal SFU modes of operation
interacts with the E2EE provided by SFrame
6.1.1. LastN and RTP stream reuse
The SFU may choose to send only a certain number of streams based on
the voice activity of the participants. To reduce the number of SDP
O/A required to establish a new RTP stream, the SFU may decide to
reuse previously existing RTP sessions or even pre-allocate a
predefined number of RTP streams and choose in each moment in time
which participant media will be sending through it.
Omara, et al. Expires 14 September 2023 [Page 19]
Internet-Draft SFrame March 2023
This means that in the same RTP stream (defined by either SSRC or
MID) may carry media from different streams of different
participants. As different keys are used by each participant for
encoding their media, the receiver will be able to verify which is
the sender of the media coming within the RTP stream at any given
point if time, preventing the SFU trying to impersonate any of the
participants with another participant's media.
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 counter
for each.
6.1.3. SVC
In both temporal and spatial scalability, the SFU may choose to drop
layers in order to match a certain bitrate or forward specific media
sizes or frames per second. In order to support it, the sender MUST
encode each spatial layer of a given picture in a different frame.
That is, an RTP frame may contain more than one SFrame encrypted
frame with an incrementing frame counter.
6.2. Video Key Frames
Forward and Post-Compromise Security requires that the e2ee keys are
updated anytime a participant joins/leave the call.
The key exchange happens async 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 encrypted frame with a key 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.
Receiver will re-request an key frame then, 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 when the new e2ee key is in use, the
time required for the new participant to display the video is
minimized.
Omara, et al. Expires 14 September 2023 [Page 20]
Internet-Draft SFrame March 2023
6.3. Partial Decoding
Some codes support partial decoding, where it can decrypt individual
packets without waiting for the full frame to arrive, with SFrame
this won't be possible because the decoder will not access the
packets until the entire frame is arrived and decrypted.
7. Security Considerations
7.1. 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.
7.2. Key Management
Key exchange mechanism is out of scope of this document, however
every client MUST change their keys when new clients joins or leaves
the call for "Forward Secrecy" and "Post Compromise Security".
7.3. Authentication tag length
The cipher suites defined in this draft use short authentication tags
for encryption, however it can easily support other ciphers with full
authentication tag if the short ones are proved insecure.
8. IANA Considerations
This document makes no requests of IANA.
9. References
9.1. Normative References
[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/rfc/rfc2119>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/rfc/rfc5116>.
Omara, et al. Expires 14 September 2023 [Page 21]
Internet-Draft SFrame March 2023
[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/rfc/rfc5869>.
[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/rfc/rfc8174>.
9.2. Informative References
[I-D.ietf-mls-architecture]
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-10, 16 December 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-mls-
architecture-10>.
[I-D.ietf-mls-protocol]
Barnes, R., Beurdouche, B., Robert, R., Millican, J.,
Omara, E., and K. Cohn-Gordon, "The Messaging Layer
Security (MLS) Protocol", Work in Progress, Internet-
Draft, draft-ietf-mls-protocol-17, 19 December 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-mls-
protocol-17>.
[I-D.murillo-perc-lite]
Murillo, S. G. and A. Gouaillard, "End to End Media
Encryption Procedures", Work in Progress, Internet-Draft,
draft-murillo-perc-lite-01, 12 May 2020,
<https://datatracker.ietf.org/doc/html/draft-murillo-perc-
lite-01>.
[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/rfc/rfc3711>.
[RFC7667] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 7667,
DOI 10.17487/RFC7667, November 2015,
<https://www.rfc-editor.org/rfc/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/rfc/rfc8723>.
Omara, et al. Expires 14 September 2023 [Page 22]
Internet-Draft SFrame March 2023
[TestVectors]
"SFrame Test Vectors", 2021,
<https://github.com/eomara/sframe/blob/master/test-
vectors.json>.
Appendix A. 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.
Appendix B. Overhead
The encryption overhead will vary between audio and video streams,
because in audio each packet is considered a separate frame, so it
will always have extra MAC and IV, however a video frame usually
consists of multiple RTP packets.
The number of bytes overhead per frame is calculated as the following
1 + FrameCounter length + 4
The constant 1 is the SFrame header byte and 4 bytes for the HBH
authentication tag for both audio and video packets.
B.1. Audio
Using three different audio frame durations
* 20ms (50 packets/s)
* 40ms (25 packets/s)
* 100ms (10 packets/s)
Up to 3 bytes frame counter (3.8 days of data for 20ms frame
duration) and 4 bytes fixed MAC length.
Omara, et al. Expires 14 September 2023 [Page 23]
Internet-Draft SFrame March 2023
+=============+===========+==========+==========+===========+
| Counter len | Packets | Overhead | Overhead | Overhead |
+=============+===========+==========+==========+===========+
| | | bps@20ms | bps@40ms | bps@100ms |
+-------------+-----------+----------+----------+-----------+
| 1 | 0-255 | 2400 | 1200 | 480 |
+-------------+-----------+----------+----------+-----------+
| 2 | 255 - 65K | 2800 | 1400 | 560 |
+-------------+-----------+----------+----------+-----------+
| 3 | 65K - 16M | 3200 | 1600 | 640 |
+-------------+-----------+----------+----------+-----------+
Table 2
B.2. Video
The per-stream overhead bits per second as calculated for the
following video encodings:
* 30fps @ 1000Kbps (4 packets per frame)
* 30fps @ 512Kbps (2 packets per frame)
* 15fps @ 200Kbps (2 packets per frame)
* 7.5fps @ 30Kbps (1 packet per frame)
Overhead bps = (Counter length + 1 + 4 ) * 8 * fps
+=============+===========+===========+===========+============+
| Counter len | Frames | Overhead | Overhead | Overhead |
+=============+===========+===========+===========+============+
| | | bps@30fps | bps@15fps | bps@7.5fps |
+-------------+-----------+-----------+-----------+------------+
| 1 | 0-255 | 1440 | 1440 | 720 |
+-------------+-----------+-----------+-----------+------------+
| 2 | 256 - 65K | 1680 | 1680 | 840 |
+-------------+-----------+-----------+-----------+------------+
| 3 | 56K - 16M | 1920 | 1920 | 960 |
+-------------+-----------+-----------+-----------+------------+
| 4 | 16M - 4B | 2160 | 2160 | 1080 |
+-------------+-----------+-----------+-----------+------------+
Table 3
Omara, et al. Expires 14 September 2023 [Page 24]
Internet-Draft SFrame March 2023
B.3. SFrame vs PERC-lite
[RFC8723] has significant overhead over SFrame because the overhead
is per packet, not per frame, and OHB (Original Header Block) which
duplicates any RTP header/extension field modified by the SFU.
[I-D.murillo-perc-lite] https://mailarchive.ietf.org/arch/msg/perc/
SB0qMHWz6EsDtz3yIEX0HWp5IEY/ is slightly better because it doesn’t
use the OHB anymore, however it still does per packet encryption
using SRTP.
Below the the overheard in [I-D.murillo-perc-lite] implemented by
Cosmos Software which uses extra 11 bytes per packet to preserve the
PT, SEQ_NUM, TIME_STAMP and SSRC fields in addition to the extra MAC
tag per packet.
OverheadPerPacket = 11 + MAC length Overhead bps = PacketPerSecond *
OverHeadPerPacket * 8
Similar to SFrame, we will assume the HBH authentication tag length
will always be 4 bytes for audio and video even though it is not the
case in this [I-D.murillo-perc-lite] implementation
B.3.1. Audio
+===================+===================+====================+
| Overhead bps@20ms | Overhead bps@40ms | Overhead bps@100ms |
+===================+===================+====================+
| 6000 | 3000 | 1200 |
+-------------------+-------------------+--------------------+
Table 4
B.3.2. Video
+=======================+====================+=====================+
| Overhead bps@30fps | Overhead bps@15fps | Overhead bps@7.5fps |
+=======================+====================+=====================+
| (4 packets per frame) | (2 packets per | (1 packet per |
| | frame) | frame) |
+-----------------------+--------------------+---------------------+
| 14400 | 7200 | 3600 |
+-----------------------+--------------------+---------------------+
Table 5
Omara, et al. Expires 14 September 2023 [Page 25]
Internet-Draft SFrame March 2023
For a conference with a single incoming audio stream (@ 50 pps) and 4
incoming video streams (@200 Kbps), the savings in overhead is 34800
- 9600 = ~25 Kbps, or ~3%.
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. For each ciphersuite, we provide:
* [in] The base_key value (hex encoded)
* [out] The secret, key, and salt values derived from the base_key
(hex encoded)
* A plaintext value that is encrypted in the following encryption
cases
* A sequence of encryption cases, including:
- [in] The KID and CTR values to be included in the header
- [out] The resulting encoded header (hex encoded)
- [out] The nonce computed from the salt and CTR values
- The ciphertext resulting from encrypting the plaintext with
these parameters (hex encoded)
An implementation should reproduce the output values given the input
values:
* An implementation should be able to encrypt with the input values
and the plaintext to produce the ciphertext.
* An implementation must be able to decrypt with the input values
and the ciphertext to generate the plaintext.
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].
C.1. AES_CTR_128_HMAC_SHA256_4
Omara, et al. Expires 14 September 2023 [Page 26]
Internet-Draft SFrame March 2023
CipherSuite: 0x01
Base Key: 101112131415161718191a1b1c1d1e1f
Key: 343d3290f5c0b936415bea9a43c6f5a2
Salt: 42d662fbad5cd81eb3aad79a
Plaintext: 46726f6d2068656176656e6c79206861
726d6f6e79202f2f205468697320756e
6976657273616c206672616d65206265
67616e
KID: 0x7
CTR: 0x0
Header: 1700
Nonce: 42d662fbad5cd81eb3aad79a
Ciphertext: 1700c5095af9dbbbed6a952de114ea7b
42768509f1ffc9749abb1e95bf4514d8
d82a0eef4b5ecac16fa193977fa1aa1c
9fa5c7e73093ab2a43
KID: 0x7
CTR: 0x1
Header: 1701
Nonce: 42d662fbad5cd81eb3aad79b
Ciphertext: 1701559e262525382885c6c93be8f61a
9064db2dd1e1e96ab1dbd829ca4af4f4
5f2b97a4889217a3f8a2159fb8201b7d
71db01702bd4bab5c7
KID: 0x7
CTR: 0x2
Header: 1702
Nonce: 42d662fbad5cd81eb3aad798
Ciphertext: 17020a8f21e052eaa09e50da0a909d15
6cc55b9ef2f2abbcca765f7af3cfb1af
234e3eac1dbc376631c83cf1ff1f8ab3
39dbc41044cc930d87
KID: 0xf
CTR: 0xaa
Header: 190faa
Nonce: 42d662fbad5cd81eb3aad730
Ciphertext: 190faa9c65aa5b167873f25827f17bc3
4879a4aaa6b38dd9584472e1849d5da5
1555f288d08f03166a5f26af01794006
255c88b58986246287c9
Omara, et al. Expires 14 September 2023 [Page 27]
Internet-Draft SFrame March 2023
KID: 0x1ff
CTR: 0xaa
Header: 1a01ffaa
Nonce: 42d662fbad5cd81eb3aad730
Ciphertext: 1a01ffaa9c65aa5b167873f25827f17b
c34879a4aaa6b38dd9584472e1849d5d
a51555f288d08f03166a5f26af017940
06255c88b589863003872e
KID: 0x1ff
CTR: 0xaaaa
Header: 2a01ffaaaa
Nonce: 42d662fbad5cd81eb3aa7d30
Ciphertext: 2a01ffaaaa990cbeb4ae2e3a76be8bb9
54b62591e791d0fa53c0553bc1d1e021
d270b1a10688cd89195203b019789253
73b04f9c08c3a4e5fb0173ef
KID: 0xffffffffffffff
CTR: 0xffffffffffffff
Header: 7fffffffffffffffffffffffffffff
Nonce: 42d662fbada327e14c552865
Ciphertext: 7fffffffffffffffffffffffffffff41
2c43c8077c286f7df3dd9988d1bd033f
1067493e09421e5bfc363e50a3c803b4
da9239514cb924dbcb5f33e33112083e
99103ef272e8
C.2. AES_CTR_128_HMAC_SHA256_8
CipherSuite: 0x02
Base Key: 202122232425262728292a2b2c2d2e2f
Key: 3fce747d505e46ec9b92d9f58ee7a5d4
Salt: 77fbf5f1d82c73f6d2b353c9
Plaintext: 46726f6d2068656176656e6c79206861
726d6f6e79202f2f205468697320756e
6976657273616c206672616d65206265
67616e
KID: 0x7
CTR: 0x0
Header: 1700
Nonce: 77fbf5f1d82c73f6d2b353c9
Ciphertext: 17009d89e5753e06edf3025f1ccd70b0
95ebaf10c250e11da740f50f57b6ce86
0d7321dfa49688a2cd6c6d9a71ae9d5c
14ad0978efe0216ae5f6788ffe
Omara, et al. Expires 14 September 2023 [Page 28]
Internet-Draft SFrame March 2023
KID: 0x7
CTR: 0x1
Header: 1701
Nonce: 77fbf5f1d82c73f6d2b353c8
Ciphertext: 1701becd2e9d10e3eed586491b3e0ece
dba89407ae2151787c5117b55707d6b8
a0754f4dc937e30ebdf7cafbd3769d65
85d7991b1aa6f36e418fdec6fa
KID: 0x7
CTR: 0x2
Header: 1702
Nonce: 77fbf5f1d82c73f6d2b353cb
Ciphertext: 170298508be6b16d034f15b504ced45a
86d1bb43ed7cd3a62bf25557d1b082b0
4e8e6ba6fe76160835dd8953e1be9640
c988627ea4f1bb846e87523f8b
KID: 0xf
CTR: 0xaa
Header: 190faa
Nonce: 77fbf5f1d82c73f6d2b35363
Ciphertext: 190faae7eec4b0556ddfb8068998351c
d670ce95f0ce9cd4c6dca2eeee73fb14
d20a0d0fd487337ed43fa7f98dad0995
b8b870325aa349ac0590c2745d5d
KID: 0x1ff
CTR: 0xaa
Header: 1a01ffaa
Nonce: 77fbf5f1d82c73f6d2b35363
Ciphertext: 1a01ffaae7eec4b0556ddfb806899835
1cd670ce95f0ce9cd4c6dca2eeee73fb
14d20a0d0fd487337ed43fa7f98dad09
95b8b870325aa31d576e8a34093320
KID: 0x1ff
CTR: 0xaaaa
Header: 2a01ffaaaa
Nonce: 77fbf5f1d82c73f6d2b3f963
Ciphertext: 2a01ffaaaa8c1789aa0abcd6abc27006
aae4df5cba4ba07f8113080e9726baac
d16c18539974a6204a36b9dc3dcd36ed
9ab48e590d95d4ad1b05f8375508c55d
Omara, et al. Expires 14 September 2023 [Page 29]
Internet-Draft SFrame March 2023
KID: 0xffffffffffffff
CTR: 0xffffffffffffff
Header: 7fffffffffffffffffffffffffffff
Nonce: 77fbf5f1d8d38c092d4cac36
Ciphertext: 7fffffffffffffffffffffffffffffa9
bc6c7edde0fdfd13255a5b145c5ce84d
b8f8960858eb998b8ea8f3e770160150
813c5806441b64251bdd2be9e8cec138
6b6f5e73eaa6c19e6555
C.3. AES_GCM_128_SHA256
CipherSuite: 0x03
Base Key: 303132333435363738393a3b3c3d3e3f
Key: 2ea2e8163ff56c0613e6fa9f20a213da
Salt: a80478b3f6fba19983d540d5
Plaintext: 46726f6d2068656176656e6c79206861
726d6f6e79202f2f205468697320756e
6976657273616c206672616d65206265
67616e
KID: 0x7
CTR: 0x0
Header: 1700
Nonce: a80478b3f6fba19983d540d5
Ciphertext: 17000e426255e47ed70dd7d15d69d759
bf459032ca15f5e8b2a91e7d348aa7c1
86d403f620801c495b1717a35097411a
a97cbb140671eb3b49ac3775926db74d
57b91e8e6c
KID: 0x7
CTR: 0x1
Header: 1701
Nonce: a80478b3f6fba19983d540d4
Ciphertext: 170103bbafa34ada8a6b9f2066bc34a1
959d87384c9f4b1ce34fed58e938bde1
43393910b1aeb55b48d91d5b0db3ea67
e3d0e02b843afd41630c940b1948e72d
d45396a43a
Omara, et al. Expires 14 September 2023 [Page 30]
Internet-Draft SFrame March 2023
KID: 0x7
CTR: 0x2
Header: 1702
Nonce: a80478b3f6fba19983d540d7
Ciphertext: 170258d58adebd8bf6f3cc0c1fcacf34
ba4d7a763b2683fe302a57f1be7f2a27
4bf81b2236995fec1203cadb146cd402
e1c52d5e6a10989dfe0f4116da1ee4c2
fad0d21f8f
KID: 0xf
CTR: 0xaa
Header: 190faa
Nonce: a80478b3f6fba19983d5407f
Ciphertext: 190faad0b1743bf5248f90869c945636
6d55724d16bbe08060875815565e90b1
14f9ccbdba192422b33848a1ae1e3bd2
66a001b2f5bb727112772e0072ea8679
ca1850cf11d8
KID: 0x1ff
CTR: 0xaa
Header: 1a01ffaa
Nonce: a80478b3f6fba19983d5407f
Ciphertext: 1a01ffaad0b1743bf5248f90869c9456
366d55724d16bbe08060875815565e90
b114f9ccbdba192422b33848a1ae1e3b
d266a001b2f5bbc9c63bd3973c19bd57
127f565380ed4a
KID: 0x1ff
CTR: 0xaaaa
Header: 2a01ffaaaa
Nonce: a80478b3f6fba19983d5ea7f
Ciphertext: 2a01ffaaaa9de65e21e4f1ca2247b879
43c03c5cb7b182090e93d508dcfb76e0
8174c6397356e682d2eaddabc0b3c101
8d2c13c3570f61c1beaab805f27b565e
1329a823a7a649b6
Omara, et al. Expires 14 September 2023 [Page 31]
Internet-Draft SFrame March 2023
KID: 0xffffffffffffff
CTR: 0xffffffffffffff
Header: 7fffffffffffffffffffffffffffff
Nonce: a80478b3f6045e667c2abf2a
Ciphertext: 7fffffffffffffffffffffffffffff09
981bdcdad80e380b6f74cf6afdbce946
839bedadd57578bfcd809dbcea535546
cc24660613d2761adea852155785011e
633534f4ecc3b8257c8d34321c27854a
1422
C.4. AES_GCM_256_SHA512
CipherSuite: 0x04
Base Key: 404142434445464748494a4b4c4d4e4f
505152535455565758595a5b5c5d5e5f
Key: 436774b0b5ae45633d96547f8f3cb06c
8e6628eff2e4255b5c4d77e721aa3355
Salt: 31ed26f90a072e6aee646298
Plaintext: 46726f6d2068656176656e6c79206861
726d6f6e79202f2f205468697320756e
6976657273616c206672616d65206265
67616e
KID: 0x7
CTR: 0x0
Header: 1700
Nonce: 31ed26f90a072e6aee646298
Ciphertext: 1700f3e297c1e95207710bd31ccc4ba3
96fbef7b257440bde638ff0f3c891154
0136df61b26220249d6c432c245ae8d5
5ef45bfccf32530a15aeaaf313a03838
e51bd45652
KID: 0x7
CTR: 0x1
Header: 1701
Nonce: 31ed26f90a072e6aee646299
Ciphertext: 170193268b0bf030071bff443bb6b447
1bdfb1cc81bc9625f4697b0336ff4665
d15f152f02169448d8a967fb06359a87
d2145398de0ce3fbe257b0992a3da153
7590459f3c
Omara, et al. Expires 14 September 2023 [Page 32]
Internet-Draft SFrame March 2023
KID: 0x7
CTR: 0x2
Header: 1702
Nonce: 31ed26f90a072e6aee64629a
Ciphertext: 1702649691ba27c4c01a41280fba4657
c03fa7fe21c8f5c862e9094227c3ca3e
c0d9468b1a2cb060ff0978f25a24e6b1
06f5a6e1053c1b8f5fce794d88a0e481
8c081e18ea
KID: 0xf
CTR: 0xaa
Header: 190faa
Nonce: 31ed26f90a072e6aee646232
Ciphertext: 190faa2858c10b5ddd231c1f26819490
521678603a050448d563c503b1fd890d
02ead01d754f074ecb6f32da9b2f3859
f380b4f47d4edd1e15f42f9a2d7ecfac
99067e238321
KID: 0x1ff
CTR: 0xaa
Header: 1a01ffaa
Nonce: 31ed26f90a072e6aee646232
Ciphertext: 1a01ffaa2858c10b5ddd231c1f268194
90521678603a050448d563c503b1fd89
0d02ead01d754f074ecb6f32da9b2f38
59f380b4f47d4e3bf7040eb10ec25b81
26b2ce7b1d9d31
KID: 0x1ff
CTR: 0xaaaa
Header: 2a01ffaaaa
Nonce: 31ed26f90a072e6aee64c832
Ciphertext: 2a01ffaaaad9bc6a258a07d210a814d5
45eca70321c0e87498ada6e5c708b7ea
d162ffcf4fbaba1eb82650590a87122b
4d95fe36bd88b278812166d26e046ed0
a530b7ee232ee0f2
Omara, et al. Expires 14 September 2023 [Page 33]
Internet-Draft SFrame March 2023
KID: 0xffffffffffffff
CTR: 0xffffffffffffff
Header: 7fffffffffffffffffffffffffffff
Nonce: 31ed26f90af8d195119b9d67
Ciphertext: 7fffffffffffffffffffffffffffffaf
480d4779ce0c02b5137ee6a61e026c04
ac999cb0c97319feceeb258d58df23bc
e14979e5c67a431777b34498062e72f9
39ca42ec84ffbc7b50eff923f515a2df
760c
Authors' Addresses
Emad Omara
Apple
Email: eomara@apple.com
Justin Uberti
Google
Email: juberti@google.com
Sergio Garcia Murillo
CoSMo Software
Email: sergio.garcia.murillo@cosmosoftware.io
Richard L. Barnes (editor)
Cisco
Email: rlb@ipv.sx
Youenn Fablet
Apple
Email: youenn@apple.com
Omara, et al. Expires 14 September 2023 [Page 34]
