Network Working Group A. Kato
Internet-Draft NTT Software Corporation
Intended status: Standards Track M. Kanda
Expires: September 5, 2007 Nippon Telegraph and Telephone
Corporation
March 4, 2007
The Additional Modes of Operation for Camellia and Its Use With IPsec
draft-kato-ipsec-camellia-modes-02
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Abstract
This document describes the use of the Camellia block cipher
algorithm in Counter (CTR) mode and Counter with CBC-MAC (CCM) Mode ,
as an IPsec Encapsulating Security Payload (ESP) mechanism to provide
confidentiality, data origin authentication, and connectionless
integrity.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. The Camellia Cipher Algorithm . . . . . . . . . . . . . . . . 5
2.1. Key Size . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Weak Keys . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Block Size and Padding . . . . . . . . . . . . . . . . . . 5
2.4. Performance . . . . . . . . . . . . . . . . . . . . . . . 5
3. Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Counter . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Counter with CBC-MAC . . . . . . . . . . . . . . . . . . . 9
4. ESP Payload . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Counter . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1.1. Counter Block Format . . . . . . . . . . . . . . . . . 12
4.1.2. Keying Material . . . . . . . . . . . . . . . . . . . 13
4.2. Counter with CBC-MAC . . . . . . . . . . . . . . . . . . . 13
4.2.1. Initialization Vector (IV) . . . . . . . . . . . . . . 13
4.2.2. Encrypted Payload . . . . . . . . . . . . . . . . . . 14
4.2.3. Authentication Data . . . . . . . . . . . . . . . . . 14
4.2.4. Nonce Format . . . . . . . . . . . . . . . . . . . . . 14
4.2.5. AAD Construction . . . . . . . . . . . . . . . . . . . 15
5. IKE Conventions . . . . . . . . . . . . . . . . . . . . . . . 17
5.1. Phase 1 Identifier . . . . . . . . . . . . . . . . . . . . 17
5.2. Phase 2 Identifier . . . . . . . . . . . . . . . . . . . . 17
5.3. Key Length Attribute . . . . . . . . . . . . . . . . . . . 17
6. Test Vectors . . . . . . . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 19
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
9.1. Normative . . . . . . . . . . . . . . . . . . . . . . . . 22
9.2. Informative . . . . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
Intellectual Property and Copyright Statements . . . . . . . . . . 26
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1. Introduction
This document describes the use of the Camellia block cipher
algorithm in Counter mode and Counter with CBC-MAC (CCM) Mode , as an
IPsec Encapsulating Security Payload (ESP) mechanism to provide
confidentiality, data origin authentication, and connectionless
integrity.
Camellia is a symmetric cipher with a Feistel structure. Camellia
was developed jointly by NTT and Mitsubishi Electric Corporation in
2000. It was designed to withstand all known cryptanalytic attacks,
and it has been scrutinized by worldwide cryptographic experts.
Camellia is suitable for implementation in software and hardware,
offering encryption speed in software and hardware implementations
that is comparable to Advanced Encryption Standard (AES) [18].
Camellia supports 128-bit block size and 128-, 192-, and 256-bit key
lengths, i.e., the same interface specifications as the AES.
Therefore, it is easy to implement Camellia based algorithms by
replacing AES block of AES based algorithms to Camellia block.
Camellia is adopted as IETF and several international standardization
organizations. Camellia is already adopted as IPSec [17], TLS [15],
S/MIME [12] and XML [14]. Camellia is adopted for the one of three
ISO/IEC international standard cipher [21] as 128bit block
cipher(Camellia AES and SEED). Camellia was selected as a
recommended cryptographic primitive by the EU NESSIE (New European
Schemes for Signatures, Integrity and Encryption) project [19] and
was included in the list of cryptographic techniques for Japanese
e-Government systems that was selected by the Japan CRYPTREC
(Cryptography Research and Evaluation Committees) [20].
Since optimized source code is provided by several open source
lisences [23], Camellia is also adopted by several open source
projects. Camellia is already adopted by Openssl. Additional API
for Network Security Services (NSS) and IPsec stack of Linux and Free
BSD are prepared or working progress for release.
The algorithm specification and object identifiers are described in
[5]. The Camellia homepage [24] contains a wealth of information
about Camellia, including detailed specification, security analysis,
performance figures, reference implementation, optimized
implementetion, test vectors, and intellectual property information.
The remainder of this document specifies the additional modes of
operation Camellia within the context of IPsec ESP. For further
information on how the various pieces of ESP fit together to provide
security services, please refer to [6] [7], and [3].
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1.1. Terminology
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" that
appear in this document are to be interpreted as described in [1].
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2. The Camellia Cipher Algorithm
All symmetric block cipher algorithms share common characteristics
and variables, including mode, key size, weak keys, block size, and
rounds. The following sections contain descriptions of the relevant
characteristics of Camellia.
The algorithm specification and object identifiers are described in
[5].
2.1. Key Size
Camellia supports three key sizes: 128 bits, 192 bits, and 256 bits.
The default key size is 128 bits, and all implementations MUST
support this key size. Implementations MAY also support key sizes of
192 bits and 256 bits.
Camellia uses a different number of rounds for each of the defined
key sizes. When a 128-bit key is used, implementations MUST use 18
rounds. When a 192-bit key is used, implementations MUST use 24
rounds. When a 256-bit key is used, implementations MUST use 24
rounds.
2.2. Weak Keys
At the time of writing this document there are no known weak keys for
Camellia.
2.3. Block Size and Padding
Camellia uses a block size of sixteen octets (128 bits).
Padding is required by the algorithms to maintain a 16-octet (128-
bit) block size. Padding MUST be added, as specified in [7], such
that the data to be encrypted (which includes the ESP Pad Length and
Next Header fields) has a length that is a multiple of 16 octets.
Because of the algorithm specific padding requirement, no additional
padding is required to ensure that the ciphertext terminates on a
4-octet boundary (i.e. maintaining a 16-octet block size guarantees
that the ESP Pad Length and Next Header fields will be right aligned
within a 4-octet word). Additional padding MAY be included, as
specified in [7], as long as the 16-octet block size is maintained.
2.4. Performance
Performance figures of Camellia are available at
<http://info.isl.ntt.co.jp/crypt/camellia/>. NESSIE project has
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reported performance of Optimized Implementations independently [19].
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3. Mode
Camellia Counter mode (Camellia-CTR) and Camellia Counter with CBC-
MAC (Camellia-CCM) are discussed in this specification.
CCM is a generic authenticate-and-encrypt block cipher mode [4]. In
this specification, CCM is used with the Camellia [5] block cipher.
3.1. Counter
Camellia-CTR requires the encryptor to generate a unique per-packet
value, and communicate this value to the decryptor. This
specification calls this per-packet value an initialization vector
(IV). The same IV and key combination MUST NOT be used more than
once. The encryptor can generate the IV in any manner that ensures
uniqueness. Common approaches to IV generation include incrementing
a counter for each packet and linear feedback shift registers
(LFSRs).
This specification calls for the use of a nonce for additional
protection against precomputation attacks. The nonce value need not
be secret. However, the nonce MUST be unpredictable prior to the
establishment of the IPsec security association that is making use of
Camellia-CTR.
Camellia-CTR has many properties that make it an attractive
encryption algorithm for in high-speed networking. Camellia-CTR uses
the Camellia block cipher to create a stream cipher. Data is
encrypted and decrypted by XORing with the key stream produced by
Camellia encrypting sequential counter block values. Camellia-CTR is
easy to implement, and Camellia-CTR can be pipelined and
parallelized. Camellia-CTR also supports key stream precomputation.
Pipelining is possible because Camellia has multiple rounds (see
section Section 2.). A hardware implementation (and some software
implementations) can create a pipeline by unwinding the loop implied
by this round structure. For example, after a 16-octet block has
been input, one round later another 16-octet block can be input, and
so on. In Camellia-CTR, these inputs are the sequential counter
block values used to generate the key stream.
Multiple independent Camellia encrypt implementations can also be
used to improve performance. For example, one could use two Camellia
encrypt implementations in parallel, to process a sequence of counter
block values, doubling the effective throughput.
The sender can precompute the key stream. Since the key stream does
not depend on any data in the packet, the key stream can be
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precomputed once the nonce and IV are assigned. This precomputation
can reduce packet latency. The receiver cannot perform similar
precomputation because the IV will not be known before the packet
arrives.
When used correctly, Camellia-CTR provides a high level of
confidentiality. Unfortunately, Camellia-CTR is easy to use
incorrectly. Being a stream cipher, any reuse of the per-packet
value, called the IV, with the same nonce and key is catastrophic.
An IV collision immediately leaks information about the plaintext in
both packets. For this reason, it is inappropriate to use this mode
of operation with static keys. Extraordinary measures would be
needed to prevent reuse of an IV value with the static key across
power cycles. To be safe, implementations MUST use fresh keys with
Camellia-CTR. The Internet Key Exchange (IKE) [8] protocol can be
used to establish fresh keys. IKE can also provide the nonce value.
With Camellia-CTR, it is trivial to use a valid ciphertext to forge
other (valid to the decryptor) ciphertexts. Thus, it is equally
catastrophic to use Camellia-CTR without a companion authentication
function. Implementations MUST use Camellia-CTR in conjunction with
an authentication function, such as Camellia-CMAC-96 [22].
To encrypt a payload with Camellia-CTR, the encryptor partitions the
plaintext, PT, into 128-bit blocks. The final block need not be 128
bits; it can be less.
PT = PT[1] PT[2] ... PT[n]
Each PT block is XORed with a block of the key stream to generate the
ciphertext, CT. The Camellia encryption of each counter block
results in 128 bits of key stream. The most significant 96 bits of
the counter block are set to the nonce value, which is 32 bits,
followed by the per-packet IV value, which is 64 bits. The least
significant 32 bits of the counter block are initially set to one.
This counter value is incremented by one to generate subsequent
counter blocks, each resulting in another 128 bits of key stream.
The encryption of n plaintext blocks can be summarized as:
CTRBLK := NONCE || IV || ONE
FOR i := 1 to n-1 DO
CT[i] := PT[i] XOR Camellia(CTRBLK)
CTRBLK := CTRBLK + 1
END
CT[n] := PT[n] XOR TRUNC(Camellia(CTRBLK))
The Camellia() function performs Camellia encryption with the fresh
key.
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The TRUNC() function truncates the output of the Camellia encrypt
operation to the same length as the final plaintext block, returning
the most significant bits.
Decryption is similar. The decryption of n ciphertext blocks can be
summarized as:
CTRBLK := NONCE || IV || ONE
FOR i := 1 to n-1 DO
PT[i] := CT[i] XOR Camellia(CTRBLK)
CTRBLK := CTRBLK + 1
END
PT[n] := CT[n] XOR TRUNC(Camellia(CTRBLK))
3.2. Counter with CBC-MAC
CCM is a generic authenticate-and-encrypt block cipher mode [4]. In
this specification, CCM is used with the Camellia [5] block cipher.
Camellia-CCM has two parameters:
M M indicates the size of the integrity check value (ICV). CCM
defines values of 4, 6, 8, 10, 12, 14, and 16 octets; However, to
maintain alignment and provide adequate security, only the values
that are a multiple of four and are at least eight are permitted.
Implementations MUST support M values of 8 octets and 16 octets,
and implementations MAY support an M value of 12 octets.
L L indicates the size of the length field in octets. CCM defines
values of L between 2 octets and 8 octets. This specification
only supports L = 4. Implementations MUST support an L value of 4
octets, which accommodates a full Jumbogram [11]; however, the
length includes all of the encrypted data, which also includes the
ESP Padding, Pad Length, and Next Header fields.
There are four inputs to CCM originator processing:
key
A single key is used to calculate the ICV using CBC-MAC and to
perform payload encryption using counter mode. Camellia supports
key sizes of 128 bits, 192 bits, and 256 bits. The default key
size is 128 bits, and implementations MUST support this key size.
Implementations MAY also support key sizes of 192 bits and 256
bits.
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nonce
The size of the nonce depends on the value selected for the
parameter L. It is 15-L octets. Implementations MUST support a
nonce of 11 octets. The construction of the nonce is described in
Section 4.2.4.
payload
The payload of the ESP packet. The payload MUST NOT be longer
than 4,294,967,295 octets, which is the maximum size of a
Jumbogram [11]; however, the ESP Padding, Pad Length, and Next
Header fields are also part of the payload.
AAD
CCM provides data integrity and data origin authentication for
some data outside the payload. CCM does not allow additional
authenticated data (AAD) to be longer than
18,446,744,073,709,551,615 octets. The ICV is computed from the
ESP header, Payload, and ESP trailer fields, which is
significantly smaller than the CCM-imposed limit. The
construction of the AAD described in Section 4.2.5.
Camellia-CCM requires the encryptor to generate a unique per-packet
value and to communicate this value to the decryptor. This per-
packet value is one of the component parts of the nonce, and it is
referred to as the initialization vector (IV). The same IV and key
combination MUST NOT be used more than once. The encryptor can
generate the IV in any manner that ensures uniqueness. Common
approaches to IV generation include incrementing a counter for each
packet and linear feedback shift registers (LFSRs).
Camellia-CCM employs counter mode for encryption. As with any stream
cipher, reuse of the same IV value with the same key is catastrophic.
An IV collision immediately leaks information about the plaintext in
both packets. For this reason, it is inappropriate to use this CCM
with statically configured keys. Extraordinary measures would be
needed to prevent reuse of an IV value with the static key across
power cycles. To be safe, implementations MUST use fresh keys with
Camellia-CCM. The Internet Key Exchange (IKE) [2] protocol or IKEv2
[8] can be used to establish fresh keys.
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4. ESP Payload
The ESP payload is made up of the IV followed by raw cipher-text.
Thus the payload field, as defined in [7], is broken down according
to the following diagram:
4.1. Counter
The Camellia counter block cipher block is 128 bits. Figure 1 shows
the format of the counter block.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initialization Vector |
| (8 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Encrypted Payload (variable) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Authentication Data (variable) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: ESP Payload Encrypted with Camellia-CTR
The components of the counter block are as follows:
Initialization Vector
The Camellia-CTR IV field MUST be eight octets. The IV MUST be
chosen by the encryptor in a manner that ensures that the same IV
value is used only once for a given key. The encryptor can
generate the IV in any manner that ensures uniqueness. Common
approaches to IV generation include incrementing a counter for
each packet and linear feedback shift registers (LFSRs).
Including the IV in each packet ensures that the decryptor can
generate the key stream needed for decryption, even when some
packets are lost or reordered.
Encrypted Payload
The encrypted payload contains the ciphertext. Camellia-CTR mode
does not require plaintext padding. However, ESP does require
padding to 32-bit word-align the authentication data. The
padding, Pad Length, and the Next Header MUST be concatenated with
the plaintext before performing encryption, as described in [7].
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Authentication Data
Since it is trivial to construct a forgery Camellia-CTR ciphertext
from a valid Camellia-CTR ciphertext, Camellia-CTR implementations
MUST employ a non-NULL ESP authentication method.
Camellia-CMAC-96 [22] is a likely choice.
4.1.1. Counter Block Format
The Camellia counter block cipher block is 128 bits. Figure 2 shows
the format of the counter block.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initialization Vector (IV) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Block Counter |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Counter Block Format
The components of the counter block are as follows:
Nonce
The Nonce field is 32 bits. As the name implies, the nonce is a
single use value. That is, a fresh nonce value MUST be assigned
for each security association. It MUST be assigned at the
beginning of the security association. The nonce value need not
be secret, but it MUST be unpredictable prior to the beginning of
the security association.
Initializetion Vector
The IV field is 64 bits. As described in section 3.1, the IV MUST
be chosen by the encryptor in a manner that ensures that the same
IV value is used only once for a given key.
Block Counter
The block counter field is the least significant 32 bits of the
counter block. The block counter begins with the value of one,
and it is incremented to generate subsequent portions of the key
stream. The block counter is a 32-bit big-endian integer value.
Using the encryption process described in Section 3.1, this
construction permits each packet to consist of up to:
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(2^32)-1 blocks = 4,294,967,295 blocks
= 68,719,476,720 octets
This construction can produce enough key stream for each packet
sufficient to handle any IPv6 jumbogram [11].
4.1.2. Keying Material
The minimum number of bits sent from the key exchange protocol to the
ESP algorithm must be greater than or equal to the key size.
The cipher's encryption and decryption key is taken from the first
128, 192, or 256 bits of the keying material.
4.2. Counter with CBC-MAC
The ESP payload is composed of the IV followed by the ciphertext.
The payload field, as defined in [7], is structured as shown in
Figure 3.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initialization Vector |
| (8 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Encrypted Payload (variable) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Authentication Data (variable) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: ESP Payload Encrypted with Camellia-CCM
4.2.1. Initialization Vector (IV)
The Camellia-CCM IV field MUST be eight octets. The IV MUST be
chosen by the encryptor in a manner that ensures that the same IV
value is used only once for a given key. The encryptor can generate
the IV in any manner that ensures uniqueness. Common approaches to
IV generation include incrementing a counter for each packet and
linear feedback shift registers (LFSRs).
Including the IV in each packet ensures that the decryptor can
generate the key stream needed for decryption, even when some
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datagrams are lost or reordered.
4.2.2. Encrypted Payload
The encrypted payload contains the ciphertext.
Camellia-CCM mode does not require plaintext padding. However, ESP
does require padding to 32-bit word-align the authentication data.
The Padding, Pad Length, and Next Header fields MUST be concatenated
with the plaintext before performing encryption, as described in [7].
When padding is required, it MUST be generated and checked in
accordance with the conventions specified in [7].
4.2.3. Authentication Data
Camellia-CCM provides an encrypted ICV. The ICV provided by CCM is
carried in the Authentication Data fields without further encryption.
Implementations MUST support ICV sizes of 8 octets and 16 octets.
Implementations MAY also support ICV 12 octets.
4.2.4. Nonce Format
Each packet conveys the IV that is necessary to construct the
sequence of counter blocks used by counter mode to generate the key
stream. The Camellia counter block is 16 octets. One octet is used
for the CCM Flags, and 4 octets are used for the block counter, as
specified by the CCM L parameter. The remaining octets are the
nonce. These octets occupy the second through the twelfth octets in
the counter block. Figure 4 shows the format of the nonce.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Salt |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initialization Vector |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Nonce Format of CCM
The components of the nonce are as follows:
Salt
The salt field is 24 bits. As the name implies, it contains an
unpredictable value. It MUST be assigned at the beginning of the
security association. The salt value need not be secret, but it
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MUST NOT be predictable prior to the beginning of the security
association.
Initialization Vector
The IV field is 64 bits. As described in Section 3.1, the IV MUST
be chosen by the encryptor in a manner that ensures that the same
IV value is used only once for a given key.
This construction permits each packet to consist of up to:
2^32 blocks = 4,294,967,296 blocks
= 68,719,476,736 octets
This construction provides more key stream for each packet than is
needed to handle any IPv6 Jumbogram [11].
4.2.5. AAD Construction
The data integrity and data origin authentication for the Security
Parameters Index (SPI) and (Extended) Sequence Number fields is
provided without encrypting them. Two formats are defined: one for
32-bit sequence numbers and one for 64-bit extended sequence numbers.
The format with 32-bit sequence numbers is shown in Figure 5, and the
format with 64-bit extended sequence numbers is shown in Figure 6.
Sequence Numbers are conveyed canonical network byte order. Extended
Sequence Numbers are conveyed canonical network byte order, placing
the high-order 32 bits first and the low-order 32 bits second.
Canonical network byte order is fully described in RFC 791, Appendix
B.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32-bit Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: AAD Format with 32-bit Sequence Number
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 64-bit Extended Sequence Number |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: AAD Format with 64-bit Sequence Number
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5. IKE Conventions
Camellia was designed to follow the same API as the AES cipher.
Therefore, this section defines only Phase 1 Identifier and Phase 2
Identifier. Any other consideration related to interaction with IKE
is the same as that of the AES cipher. Details can be found in IKE
Conventions section of [13] and [16].
5.1. Phase 1 Identifier
This document does not specify the conventions for using Camellia-CTR
and Camellia-CCM for IKE Phase 1 negotiations. For Camellia-CTR and
Camellia-CCM to be used in this manner, a separate specification is
needed, and an Encryption Algorithm Identifier needs to be assigned.
5.2. Phase 2 Identifier
For IKE Phase 2 negotiations, IANA has assigned three ESP Transform
Identifiers for Camellia-CTR and Camellia-CCM.
<TBD1> for Camellia-CTR with and explict IV;
<TBD2> for Camellia-CCM with an 8-octet ICV;
<TBD3> for Camellia-CCM with a 12-octet ICV; and
<TBD4> for Camellia-CCM with a 16-octet ICV.
5.3. Key Length Attribute
Since the Camellia supports three key lengths, the Key Length
attribute MUST be specified in the IKE Phase 2 exchange [10]. The
Key Length attribute MUST have a value of 128, 192, or 256.
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6. Test Vectors
<TBD>
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7. Security Considerations
Camellia-CTR and Camellia-CCM employs counter (CTR) mode for
confidentiality. If a counter value is ever used for more that one
packet with the same key, then the same key stream will be used to
encrypt both packets, and the confidentiality guarantees are voided.
What happens if the encryptor XORs the same key stream with two
different packet plaintexts? Suppose two packets are defined by two
plaintext byte sequences P1, P2, P3 and Q1, Q2, Q3, then both are
encrypted with key stream K1, K2, K3. The two corresponding
ciphertexts are:
(P1 XOR K1), (P2 XOR K2), (P3 XOR K3)
(Q1 XOR K1), (Q2 XOR K2), (Q3 XOR K3)
If both of these two ciphertext streams are exposed to an attacker,
then a catastrophic failure of confidentiality results, because:
(P1 XOR K1) XOR (Q1 XOR K1) = P1 XOR Q1
(P2 XOR K2) XOR (Q2 XOR K2) = P2 XOR Q2
(P3 XOR K3) XOR (Q3 XOR K3) = P3 XOR Q3
Once the attacker obtains the two plaintexts XORed together, it is
relatively straightforward to separate them. Thus, using any stream
cipher, including Camellia-CTR, to encrypt two plaintexts under the
same key stream leaks the plaintext.
Therefore, Camellia-CTR and Camellia-CCM should not be used with
statically configured keys. Extraordinary measures would be needed
to prevent the reuse of a counter block value with the static key
across power cycles. To be safe, implementations MUST use fresh keys
with Camellia-CTR and Camellia-CCM. The IKE [2] and IKEv2 [8]
protocol can be used to establish fresh keys.
When IKE is used to establish fresh keys between two peer entities,
separate keys are established for the two traffic flows. If a
different mechanism is used to establish fresh keys, one that
establishes only a single key to encrypt packets, then there is a
high probability that the peers will select the same IV values for
some packets. Thus, to avoid counter block collisions, ESP
implementations that permit use of the same key for encrypting and
decrypting packets with the same peer MUST ensure that the two peers
assign different salt values to the security association (SA).
Regardless of the mode used, Camellia with a 128-bit key is
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vulnerable to the birthday attack after 2^64 blocks are encrypted
with a single key. Since ESP with Extended Sequence Numbers allows
for up to 2^64 packets in a single SA, there is real potential for
more than 2^64 blocks to be encrypted with one key. Implementations
SHOULD generate a fresh key before 2^64 blocks are encrypted with the
same key. Note that ESP with 32-bit Sequence Numbers will not exceed
2^64 blocks even if all of the packets are maximum-length Jumbograms.
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8. IANA Considerations
IANA has assigned three ESP transform numbers for use with Camellia-
CTR and Camellia-CCM:
<TBD1> for Camellia-CTR with and explict IV;
<TBD2> for Camellia-CCM with an 8-octet ICV;
<TBD3> for Camellia-CCM with a 12-octet ICV; and
<TBD4> for Camellia-CCM with a 16-octet ICV.
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9. References
9.1. Normative
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
RFC 2409, November 1998.
[3] Thayer, R., Doraswamy, N., and R. Glenn, "IP Security Document
Roadmap", RFC 2411, November 1998.
[4] Whiting, D., Housley, R., and N. Ferguson, "Counter with CBC-
MAC (CCM)", RFC 3610, September 2003.
[5] Matsui, M., Nakajima, J., and S. Moriai, "A Description of the
Camellia Encryption Algorithm", RFC 3713, April 2004.
[6] Kent, S. and K. Seo, "Security Architecture for the Internet
Protocol", RFC 4301, December 2005.
[7] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303,
December 2005.
[8] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[9] Dworkin, M., "Recommendation for Block Cipher Modes of
Operation - Methods and Techniques", NIST Special
Publication 800-38A, November 2001, <http://csrc.nist.gov/
publications/nistpubs/800-38a/sp800-38a.pdf>.
9.2. Informative
[10] Piper, D., "The Internet IP Security Domain of Interpretation
for ISAKMP", RFC 2407, November 1998.
[11] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms",
RFC 2675, August 1999.
[12] Moriai, S. and A. Kato, "Use of the Camellia Encryption
Algorithm in Cryptographic Message Syntax (CMS)", RFC 3657,
January 2004.
[13] Housley, R., "Using Advanced Encryption Standard (AES) Counter
Mode With IPsec Encapsulating Security Payload (ESP)",
RFC 3686, January 2004.
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[14] Eastlake, D., "Additional XML Security Uniform Resource
Identifiers (URIs)", RFC 4051, April 2005.
[15] Moriai, S., Kato, A., and M. Kanda, "Addition of Camellia
Cipher Suites to Transport Layer Security (TLS)", RFC 4132,
July 2005.
[16] Housley, R., "Using Advanced Encryption Standard (AES) CCM Mode
with IPsec Encapsulating Security Payload (ESP)", RFC 4309,
December 2005.
[17] Kato, A., Moriai, S., and M. Kanda, "The Camellia Cipher
Algorithm and Its Use With IPsec", RFC 4312, December 2005.
[18] National Institute of Standards and Technology, "Advanced
Encryption Standard (AES)", FIPS PUB 197, November 2001,
<http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf>.
[19] "The NESSIE project (New European Schemes for Signatures,
Integrity and Encryption)",
<http://www.cosic.esat.kuleuven.ac.be/nessie/>.
[20] Information-technology Promotion Agency (IPA), "Cryptography
Research and Evaluation Committees",
<http://www.ipa.go.jp/security/enc/CRYPTREC/index-e.html>.
[21] International Organization for Standardization, "Information
technology - Security techniques - Encryption algorithms - Part
3: Block ciphers", ISO/IEC 18033-3, July 2005.
[22] Kato, A., Kanda, M., and T. Iwata, "The Camellia-CMAC-96 and
Camellia-CMAC-PRF-128 Algorithms and Its Use with IPsec",
draft-kato-ipsec-camellia-cmac96and128-00 (work in progress),
February 2007.
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URIs
[23] <http://info.isl.ntt.co.jp/crypt/eng/camellia/source.html>
[24] <http://info.isl.ntt.co.jp/camellia/>
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Authors' Addresses
Akihiro Kato
NTT Software Corporation
Phone: +81-45-212-7094
Fax: +81-45-212-7506
Email: akato@po.ntts.co.jp
Masayuki Kanda
Nippon Telegraph and Telephone Corporation
Phone: +81-46-859-2437
Fax: +81-46-859-3365
Email: kanda@isl.ntt.co.jp
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