AVT Working Group W. Kim
Internet Draft J. Lee
Intended status: Standard Track D. Kim
Expires: June 20, 2011 D. Kwon
C. Kim
NSRI
December 22, 2010
The ARIA Algorithm and Its Use with the Secure Real-time Transport
Protocol(SRTP)
draft-nsri-avt-aria-srtp-01.txt
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Abstract
This document describes the use of the ARIA block cipher algorithm
in the Secure Real-time Transport Protocol (SRTP) for providing
confidentiality for the Real-time Transport Protocol (RTP) traffic
and for the control traffic for RTP, the Real-time Transport Control
Protocol (RTCP).
1. Introduction
This document describes the use of the ARIA [RFC5794] block cipher
algorithm in the Secure Real-time Transport Protocol (SRTP) [RFC3711]
for providing confidentiality for the Real-time Transport Protocol
(RTP) [RFC3550] traffic and for the control traffic for RTP, the
Real-time Transport Control Protocol (RTCP) [RFC3550].
1.1. ARIA
ARIA is a general-purpose block cipher algorithm developed by Korean
cryptographers in 2003. It is an iterated block cipher with 128-,
192-, and 256-bit keys and encrypts 128-bit blocks in 12, 14, and 16
rounds, depending on the key size. It is secure and suitable for
most software and hardware implementations on 32-bit and 8-bit
processors. It was established as a Korean standard block cipher
algorithm in 2004 [ARIAKS] and has been widely used in Korea,
especially for government-to-public services. It was included in
PKCS #11 in 2007 [ARIAPKCS]. The algorithm specification and object
identifiers are described in [RFC5794].
1.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
1.3. Definitions
|| concatenation
XOR exclusive or
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2. Cryptographic Transforms
All symmetric block cipher algorithms share common characteristics
including mode, key size, weak keys, and block size. The following
sections contain descriptions of the relevant characteristics of
ARIA.
ARIA does not have any restrictions for modes of operation that are
used with this block cipher. We define three modes of running ARIA,
(1) ARIA in Counter Mode, (2) ARIA in Counter with CBC-MAC (CCM)
Mode and (3) ARIA in Galois/Counter Mode (GCM) Mode.
2.1. Counter
Section 4.1.1 of [RFC3711] defines AES counter mode encryption,
which it refers to as AES-CM. ARIA counter mode is defined in a
similar manner, and is denoted as ARIA-CTR. The plaintext inputs to
the block cipher are formed as in AES-CM, and the block cipher
outputs are processed as in AES-CM. The only difference in the
processing is that ARIA-CTR uses ARIA as the underlying encryption
primitive. When ARIA-CTR is used, it MUST be used only in
conjunction with an authentication function.
2.1.1. Message Authentication/Integrity: HMAC-SHA1
HMAC-SHA1 [RFC2104], as defined in section 4.2.1 of [RFC3711], SHALL
be the default message authentication code to be used with ARIA-CTR.
The default session authentication key-length SHALL be 160 bits, the
default authentication tag length SHALL be 80 bits, and the
SRTP_PREFIX_LENGTH SHALL be zero for HMAC-SHA1. For SRTP, smaller
values are NOT RECOMMENDED, but MAY be used after careful
consideration of the issues in section 7.5 and 9.5 of [RFC3711].
2.2. Counter with CBC-MAC (CCM)
CCM is a generic authenticate-and-encrypt block cipher mode
[RFC3610]. In this specification, CCM used with the ARIA block
cipher is denoted as ARIA-CCM. Section 3.3 of [RFC3711] defines
procedures to construct or to authenticate and decrypt SRTP packets.
For ARIA-CCM however, the sender performs Step 7 before Step 5 and
the receiver performs the second half of Step 5 (performs
verification) after Step 6. This means that authentication is
performed on the plaintext rather than the ciphertext. This applies
equally to SRTCP
All SRTP packets MUST be authenticated and encrypted. Unlike SRTP,
SRTCP packet encryption is optional (but authentication is
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mandatory). A sender can select which packets to encrypt, and
indicates this choice with a 1-bit encryption flag (located in the
leftmost bit of the 32-bit word that contains the SRTCP index).
ARIA-CCM has two parameters:
M M indicates the size of the authentication tag. In SRTP, a
full 80-bit authentication-tag SHOULD be used and
implementation of this specification MUST support M values of
10 octets.
L L indicates the size of the length field in octets. The number
of octets in the nonce MUST be 12, i.e., L is 3.
ARIA-CCM has four inputs:
Key
A single key is used to calculate the authentication tag using
CBC-MAC and to perform payload encryption using counter mode.
ARIA only supports a key size of 128 bits.
Nonce
The size of the nonce depends on the value selected for the
parameter L. It is 15-L octets. L equals 3 and hence the nonce
size equals 12 octets.
Plaintext
In case of SRTP, the payload of the RTP packet and the RTP
padding and RTP pad count field (if the latter two fields are
present).
In case of SRTCP, when the encryption flag is set to 1, the
Encrypted Portion described in Fig.2 of [RFC3711] is treated as
plaintext. When the encryption flag is set to 0, the plaintext
is zero-length.
Additional Authentication Data (AAD)
In case of SRTP, the header of the RTP packet including
contributing source (CSRC) identifier (if present) and the RTP
header extension (if present).
In case of SRTCP, when the encryption flag is set to 0, the
Authentication Portion described in Fig.2 of [RFC3711] is
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treated as AAD. When the encryption flag is set to 1, the first
8-octets, the encryption flag and SRTCP index are treated as
AAD.
ARIA-CCM accepts these four inputs and returns a ciphertext field.
2.3. Galois/Counter Mode (GCM)
GCM is a block cipher mode of operation providing both
confidentiality and data origin authentication [GCM]. GCM used with
the ARIA block cipher is denoted as ARIA-GCM.
ARIA-GCM has four inputs: a key, a plaintext, a nonce and the
additional authenticated data (AAD) all described in section 2.2.
The bit length of the tag, denoted t, is 12, and an authentication
tag with a length of 12 octets (96 bits) is used.
3. Nonce Format for CCM and GCM
3.1. Nonce for SRTP
The nonce for SRTP SHALL be formed in the following way:
Nonce = (16 bits of zeroes || SSRC || ROC || SEQ) XOR Salt
The 4-octet SSRC and the 2-octet SEQ SHALL be taken from the RTP
header. The 4-octet ROC is from the cryptographic context. The 12-
octet Salt SHALL be produced by the SRTP Key Derivation Function.
3.2. Nonce for SRTCP
The nonce for SRTCP SHALL be formed in the following way:
Nonce = (16 bits of zeroes || SSRC || 16 bits of zeroes ||
SRTCP index) XOR Salt
The 4-octet SSRC SHALL be taken from the RTCP header and the 31-bit
SRTCP index (packed zero-filled, right justified into a 4-octet
field) is from each packet. The 12-octet Salt SHALL be produced by
the SRTP Key Derivation Function.
4. Key Derivation: ARIA-CTR PRF
Section 4.3.3 of [RFC3711] defines the AES-128 counter mode key
derivation function, which it refers to as "AES-CM PRF". The ARIA-
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CTR PRF is defined in a similar manner, but with each invocation of
AES replaced with an invocation of ARIA.
The currently defined PRF, keyed by the 128-bit master key, has
input block size m = 128 and can produce n-bit outputs for n up to
2^23. ARIA-PRF_n(k_master, x) SHALL be ARIA in Counter Mode as
described in section 2.1, applied to key k_master, and IV equal to
(x*2^16), and with the output keystream truncated to the n first
(left-most) bits.
5. Mandatory-to-implement Transforms
"Mandatory-to-implement" means conformance to this specification,
and that Table 1 does not supersede a similar table in section 5 of
[RFC3711]. An RTP implementation that supports ARIA MUST implement
the modes listed in Table 1.
mandatory-to-implement optional
encryption ARIA-CTR ARIA-CCM,ARIA-GCM
message integrity HMAC-SHA1 ARIA-CCM,ARIA-GCM
key derivation (PRF) ARIA-CTR -
Table 1: Mandatory-to-implement and optional transforms in SRTP and
SRTCP.
6. Security Considerations
At the time of writing this document no security problem has been
found on ARIA (see [YWL]).
The security considerations in [RFC3711] apply to this document as
well.
See [RFC3610] and [GCM] for security considerations regarding the
CCM and GCM modes of operations, respectively.
7. IANA Considerations
[RFC4568] defines SRTP "crypto suites". In order to allow SDP to
signal the use of the algorithms defined in this document, IANA will
register the following crypto suites into the subregistry for SRTP
crypto suites under the SRTP transport of the SDP Security
Descriptions:
srtp-crypto-suite-ext = "ARIA_CTR_128_HMAC_SHA1_80"/
"ARIA_128_CCM_80"/
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"ARIA_128_GCM_96"/
srtp-crypto-suite-ext
8. References
8.1. Normative References
[GCM] Dworkin, M., "NIST Special Publication 800-38D:
Recommendation for Block Cipher Modes of Operation:
Galois/Counter Mode (GCM) and GMAC", U.S. National
Institute of Standards and Technology
http://csrc.nist.gov/publications/nistpubs/800-38D/SP-
800-38D.pdf
[RFC2104] Krawczyk, H.,Bellare, M. and Canetti, R., "HMAC: keyed
Hashing for Message Authentication", RFC 2104, February
1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R. and Jacobson,
V. "RTP: A Transport Protocol for Real-time Applications"
, RFC3550, July 2003.
[RFC3610] Whiting, D., Housley, R., and N. Ferguson, "Counter with
CBC-MAC (CCM)", RFC 3610, September 2003.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E.,
Norrman, K., "The Secure Real-time Transport Protocol
(SRTP)", RFC 3711, March 2004.
[RFC4568] Andreasen, F., Baugher, M., Wing, D., "Session
Description Protocol (SDP) Security Descriptions for
Media Streams", RFC 4568, July 2006.
[RFC5794] Lee, J., Lee, J., Kim, J., Kwon, D. and Kim, C., "A
Description of the ARIA Encryption Algorithm", RFC 5794,
March 2010.
8.2. Informative References
[YWL] Li, Y., Wu, W. and Zhang, L., "Integral attacks on
reduced-round ARIA block cipher", ISPEC 2010, LNCS,
vol.6047, pp.19-29, 2010.
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[ARIAKS] Korean Agency for Technology and Standards (KATS), "128
bit block encryption algorithm ARIA ?Part 1: General",
KS X 1213-1:2009, December 2009 (In Korean).
[ARIAPKCS] RSA Laboratories, PKCS #11 v2.20 Amendment 3 Revision 1:
Additional PKCS #11 Mechanisms, January 2007.
APPENDIX A: Test Vectors
All Values are in hexadecimal.
A.1. ARIA-CTR Test Vectors
Session Key: 0c5ffd37a11edc42c325287fc0604f2e
Rollover Counter: 00000000
Sequence Number: 315e
SSRC: 20e8f5eb
Authentication Key: f93563311b354748c97891379553063116452309
Session Salt: cd3a7c42c671e0067a2a2639b43a
Initialization Vector: cd3a7c42e69915ed7a2a263985640000
RTP header: 8008315ebf2e6fe020e8f5eb
RTP Payload: f57af5fd4ae19562976ec57a5a7ad55a
5af5c5e5c5fdf5c55ad57a4a7272d572
62e9729566ed66e97ac54a4a5a7ad5e1
5ae5fdd5fd5ac5d56ae56ad5c572d54a
e54ac55a956afd6aed5a4ac562957a95
16991691d572fd14e97ae962ed7a9f4a
955af572e162f57a956666e17ae1f54a
95f566d54a66e16e4afd6a9f7ae1c5c5
5ae5d56afde916c5e94a6ec56695e14a
fde1148416e94ad57ac5146ed59d1cc5
Encrypted RTP Payload: 1bf753f412e6f35058cc398dc851aae3
a6ccdcb463fbed9cfb3de2fb76fdffa9
e481f5efb64c92487f59dabbc7cc72da
092485f3fbad87888820b86037311fa4
4330e18a59a1e1338ba2c21458493a57
463475c54691f91cec785429119e0dfc
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d9048f90e07fecd50b528e8c62ee6e71
445de5d7f659405135aff3604c2ca4ff
4aaca40809cb9eee42cc4ad232307570
81ca289f2851d3315e9568b501fdce6d
Authenticated portion || Rollover Counter:
8008315ebf2e6fe020e8f5eb1bf753f4
12e6f35058cc398dc851aae3a6ccdcb4
63fbed9cfb3de2fb76fdffa9e481f5ef
b64c92487f59dabbc7cc72da092485f3
fbad87888820b86037311fa44330e18a
59a1e1338ba2c21458493a57463475c5
4691f91cec785429119e0dfcd9048f90
e07fecd50b528e8c62ee6e71445de5d7
f659405135aff3604c2ca4ff4aaca408
09cb9eee42cc4ad23230757081ca289f
2851d3315e9568b501fdce6d00000000
Tag: f9de4e729054672b0e35
A.2. ARIA-CCM Test Vectors
Key: 974bee725d44fc3992267b284c3c6750
Rollover Counter: 00000000
Sequence Number: 315e
SSRC: 20e8f5eb
Nonce: 000020e8f5eb00000000315e
Payload: f57af5fd4ae19562976ec57a5a7ad55a
5af5c5e5c5fdf5c55ad57a4a7272d572
62e9729566ed66e97ac54a4a5a7ad5e1
5ae5fdd5fd5ac5d56ae56ad5c572d54a
e54ac55a956afd6aed5a4ac562957a95
16991691d572fd14e97ae962ed7a9f4a
955af572e162f57a956666e17ae1f54a
95f566d54a66e16e4afd6a9f7ae1c5c5
5ae5d56afde916c5e94a6ec56695e14a
fde1148416e94ad57ac5146ed59d1cc5
AAD: 8008315ebf2e6fe020e8f5eb
Encrypted RTP Payload: 621e408a2e455505b39f704dcbac4307
daabbd6d670abc4e42f2fd2fca263f09
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4f4683e6fb0b10c5093d42b69dce0ba5
46520e7c4400975713f3bde93e13116
0b9cbcd6df78a1502be7c6ea8d395b9e
d0078819c3105c0ab92cb67b16ba51bb
1f53508738bf7a37c9a905439b88b7af
9d51a407916fdfea8d43bf253721846d
c1671391225fc58d9d0693c8ade6a4ff
b034ee6543dd4e651b7a084eae60f855
Authentication Tag: 0ed04a301790ad92955d
A.3. ARIA-GCM Test Vectors
Key: e91e5e75da65554a48181f3846349562
Rollover Counter: 00000000
Sequence Number: 315e
SSRC: 20e8f5eb
Nonce: 000020e8f5eb00000000315e
Payload: f57af5fd4ae19562976ec57a5a7ad55a
5af5c5e5c5fdf5c55ad57a4a7272d572
62e9729566ed66e97ac54a4a5a7ad5e1
5ae5fdd5fd5ac5d56ae56ad5c572d54a
e54ac55a956afd6aed5a4ac562957a95
16991691d572fd14e97ae962ed7a9f4a
955af572e162f57a956666e17ae1f54a
95f566d54a66e16e4afd6a9f7ae1c5c5
5ae5d56afde916c5e94a6ec56695e14a
fde1148416e94ad57ac5146ed59d1cc5
AAD: 8008315ebf2e6fe020e8f5eb
Encrypted RTP Payload: 4d8a9a0675550c704b17d8c9ddc81a5c
d6f7da34f2fe1b3db7cb3dfb9697102e
a0f3c1fc2dbc873d44bceeae8e444297
4ba21ff6789d3272613fb9631a7cf3f1
4bacbeb421633a90ffbe58c2fa6bdca5
34f10d0de0502ce1d531b6336e588782
78531e5c22bc6c85bbd784d78d9e680a
a19031aaf89101d669d7a3965c1f7e16
229d7463e0535f4e253f5d18187d40b8
ae0f564bd970b5e7e2adfb211e89a953
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Authentication Tag: 5abace3f37f5a736f4be984b
A.4. Key Derivation Test Vector
This section provides data for the default key derivation function,
which uses ARIA-128 in Counter Mode. In the following, we walk
through the initial key derivation for the ARIA-128 Counter Mode
cipher, which requires a 16 octet session encryption key and a 14
octet session salt, and an authentication function which requires a
94 octet session authentication key. These values are called the
cipher key, the cipher salt, and the auth key in the following. The
test vectors are generated in a similar way with the test vector of
key derivation function in [RFC3711] but with each invocation of AES
replaced with an invocation of ARIA.
The inputs to the key derivation function are the 16 octet master
key and the 14 octet master salt:
master key: e1f97a0d3e018be0d64fa32c06de4139
master salt: 0ec675ad498afeebb6960b3aabe6
index DIV kdr: 000000000000
label: 00
master salt: 0ec675ad498afeebb6960b3aabe6
-----------------------------------------------
xor: 0ec675ad498afeebb6960b3aabe6 (x, PRF input)
x*2^16: 0ec675ad498afeebb6960b3aabe60000 (ARIA-CTR input)
cipher key: dbd85a3c4d9219b3e81f7d942e299de4 (ARIA-CTR output)
ARIA-CTR cipher suite requires 14 octet cipher salt while ARIA-CCM
and ARIA-GCM cipher suites require 12 octet cipher salt.
index DIV kdr: 000000000000
label: 02
master salt: 0ec675ad498afeebb6960b3aabe6
----------------------------------------------
xor: 0ec675ad498afee9b6960b3aabe6 (x, PRF input)
x*2^16: 0ec675ad498afee9b6960b3aabe60000 (ARIA-CTR input)
9700657f5f34161830d7d85f5dc8be7f (ARIA-CTR output)
cipher salt: 9700657f5f34161830d7d85f5dc8 (ARIA-CTR cipher
suite)
9700657f5f34161830d7d85f (ARIA-CCM or
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ARIA-GCM cipher suite)
index DIV kdr: 000000000000
label: 01
master salt: 0ec675ad498afeebb6960b3aabe6
-----------------------------------------------
xor: 0ec675ad498afeeab6960b3aabe6 (x, PRF input)
x*2^16: 0ec675ad498afeeab6960b3aabe60000 (ARIA-CTR input)
Below, the auth key is shown on the left, while the corresponding
ARIA input blocks are shown on the right.
auth key ARIA input blocks
d021877bd3eaf92d581ed70ddc050e03 0ec675ad498afeeab6960b3aabe60000
f11257032676f2a29f57b21abd3a1423 0ec675ad498afeeab6960b3aabe60001
769749bdc5dd9ca5b43ca6b6c1f3a7de 0ec675ad498afeeab6960b3aabe60002
4047904bcf811f601cc03eaa5d7af6db 0ec675ad498afeeab6960b3aabe60003
9f88efa2e51ca832fc2a15b126fa7be2 0ec675ad498afeeab6960b3aabe60004
469af896acb1852c31d822c45799 0ec675ad498afeeab6960b3aabe60005
Authors' Addresses
Woo-Hwan Kim
National Security Research Institute
P.O.Box 1, Yuseong, Daejeon, 305-350, Korea
Email: whkim5@ensec.re.kr
Jungkeun Lee
National Security Research Institute
P.O.Box 1, Yuseong, Daejeon, 305-350, Korea
Email: jklee@ensec.re.kr
Dong-Chan Kim
National Security Research Institute
P.O.Box 1, Yuseong, Daejeon, 305-350, Korea
Email: dongchan@ensec.re.kr
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Daesung Kwon
National Security Research Institute
P.O.Box 1, Yuseong, Daejeon, 305-350, Korea
Email: ds_kwon@ensec.re.kr
Choonsoo Kim
National Security Research Institute
P.O.Box 1, Yuseong, Daejeon, 305-350, Korea
Email: jbr@ensec.re.kr
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