S/MIME Working Group S. Moriai
Internet Draft NTT Corporation
Expiration Date: September 2003 A. Kato
NTT Software Corporation
March 2003
Use of the Camellia Encryption Algorithm in CMS
Status of this Memo
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Abstract
This document specifies how to incorporate the Camellia encryption
algorithm into the S/MIME Cryptographic Message Syntax (CMS) as an
additional algorithm for symmetric encryption. The relevant object
identifiers (OIDs) and processing steps are provided so that
Camellia may be used in the CMS specification (RFC 3369, RFC 3370)
for content and key encryption.
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD
NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document (in
uppercase, as shown) are to be interpreted as described in
[RFC2119].
1. Introduction
This document specifies the conventions for using the Camellia
encryption algorithm [CamelliaSpec][CamelliaID] for encryption with
the Cryptographic Message Syntax (CMS) [CMS].
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CMS values are generated using ASN.1 (X.208-88), using the Basic
Encoding Rules (BER) (X.209-88) and the Distinguished Encoding Rules
(DER) (X.509-88).
1.1 Camellia
Camellia was jointly developed by Nippon Telegraph and Telephone
Corporation and Mitsubishi Electric Corporation in 2000. Camellia
specifies the 128-bit block size and 128-, 192-, and 256-bit key
sizes, the same interface as the Advanced Encryption Standard (AES).
Camellia is characterized by its suitability for both software and
hardware implementations as well as its high level of security.
From a practical viewpoint, it is designed to enable flexibility in
software and hardware implementations on 32-bit processors widely
used over the Internet and many applications, 8-bit processors used
in smart cards, cryptographic hardware, embedded systems, and so on
[CamelliaTech]. Moreover, its key setup time is excellent, and its
key agility is superior to that of AES.
Camellia has been scrutinized by the wide cryptographic community
during several projects for evaluating crypto algorithms. In
particular, Camellia was selected as a recommended cryptographic
primitive by the EU NESSIE (New European Schemes for Signatures,
Integrity and Encryption) project [NESSIE] and also included in the
list of cryptographic techniques for Japanese e-Government systems
which are selected by the Japan CRYPTREC (Cryptography Research and
Evaluation Committees) [CRYPTREC].
2. Object Identifiers for Content and Key Encryption
This section provides the OIDs and processing information necessary
for Camellia to be used for content and key encryption in CMS.
Camellia is added to the set of optional symmetric encryption
algorithms in CMS by providing two classes of unique object
identifiers (OIDs). One OID class defines the content encryption
algorithms and the other defines the key encryption algorithms.
Thus a CMS agent can apply Camellia either for content or key
encryption by selecting the corresponding object identifier,
supplying the required parameter, and starting the program code.
2.1 OIDs for Content Encryption
Camellia is added to the set of symmetric content encryption
algorithms defined in [CMSALG]. The Camellia content-encryption
algorithm, in Cipher Block Chaining (CBC) mode, for the three
different key sizes are identified by the following object
identifiers:
id-camellia128-cbc OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) 392 200011 61 security(1)
algorithm(1) symmetric-encryption-algorithm(1)
camellia128-cbc(2) }
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id-camellia192-cbc OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) 392 200011 61 security(1)
algorithm(1) symmetric-encryption-algorithm(1)
camellia192-cbc(3) }
id-camellia256-cbc OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) 392 200011 61 security(1)
algorithm(1) symmetric-encryption-algorithm(1)
camellia256-cbc(4) }
The AlgorithmIdentifier parameters field MUST be present, and the
parameters field MUST contain the value of IV:
CamelliaCBCParameter ::= CamelliaIV -- Initialization Vector
CamelliaIV ::= OCTET STRING (SIZE(16))
The plain text is padded according to Section 6.3 of [CMS].
2.2 OIDs for Key Encryption
The key-wrap/unwrap procedures used to encrypt/decrypt a Camellia
content-encryption key (CEK) with a Camellia key-encryption key
(KEK) are specified in Section 3. Generation and distribution of
key-encryption keys are beyond the scope of this document.
The Camellia key-encryption algorithm has the following object
identifier:
id-camellia128-wrap OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) 392 200011 61 security(1)
algorithm(1) key-wrap-algorithm(3)
camellia128-wrap(2) }
id-camellia192-wrap OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) 392 200011 61 security(1)
algorithm(1) key-wrap-algorithm(3)
camellia192-wrap(3) }
id-camellia256-wrap OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) 392 200011 61 security(1)
algorithm(1) key-wrap-algorithm(3)
camellia256-wrap(4) }
In all cases the parameters field of AlgorithmIdentifier MUST be
absent, because the key wrapping procedure itself defines how and
when to use an IV. The OID gives the KEK key size, but does not
make any statements as to the size of the wrapped Camellia CEK.
Implementations MAY use different KEK and CEK sizes. Implements
MUST support the CEK and the KEK having the same length. If
different lengths are supported, the KEK MUST be of equal or greater
length than the CEK.
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3. Key Wrap Algorithm
Camellia key wrapping and unwrapping is done in conformance with the
AES key wrap algorithm [AES-WRAP][RFC3394], because Camellia and AES
have the same block and key sizes, i.e. the block size of 128 bits
and key sizes of 128, 192, and 256 bits.
3.1 Notation and Definitions
The following notation is used in the description of the key
wrapping algorithms:
Camellia(K, W)
Encrypt W using the Camellia codebook with key K
Camellia-1(K, W)
Decrypt W using the Camellia codebook with key K
MSB(j, W) Return the most significant j bits of W
LSB(j, W) Return the least significant j bits of W
B1 ^ B2 The bitwise exclusive or (XOR) of B1 and B2
B1 | B2 Concatenate B1 and B2
K The key-encryption key K
n The number of 64-bit key data blocks
s The number of steps in the wrapping process, s = 6n
P[i] The ith plaintext key data block
C[i] The ith ciphertext data block
A The 64-bit integrity check register
R[i] An array of 64-bit registers where
i = 0, 1, 2, ..., n
A[t], R[i][t] The contents of registers A and R[i] after encryption
step t.
IV The 64-bit initial value used during the wrapping
process.
In the key wrap algorithm, the concatenation function will be used
to concatenate 64-bit quantities to form the 128-bit input to the
Camellia codebook. The extraction functions will be used to split
the 128-bit output from the Camellia codebook into two 64-bit
quantities.
3.2 Camellia Key Wrap
Key wrapping with Camellia is identical to Section 2.2.1 of
[RFC3394] with "AES" replaced by "Camellia".
The inputs to the key wrapping process are the KEK and the plaintext
to be wrapped. The plaintext consists of n 64-bit blocks,
containing the key data being wrapped. The key wrapping process is
described below.
Inputs: Plaintext, n 64-bit values {P1, P2, ..., Pn}, and
Key, K (the KEK).
Outputs: Ciphertext, (n+1) 64-bit values {C0, C1, ..., Cn}.
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1) Initialize variables.
Set A0 to an initial value (see Section 3.4)
For i = 1 to n
R[0][i] = P[i]
2) Calculate intermediate values.
For t = 1 to s, where s = 6n
A[t] = MSB(64, Camellia(K, A[t-1] | R[t-1][1])) ^ t
For i = 1 to n-1
R[t][i] = R[t-1][i+1]
R[t][n] = LSB(64, Camellia(K, A[t-1] | R[t-1][1]))
3) Output the results.
Set C[0] = A[t]
For i = 1 to n
C[i] = R[t][i]
An alternative description of the key wrap algorithm involves
indexing rather than shifting. This approach allows one to
calculate the wrapped key in place, avoiding the rotation in the
previous description. This produces identical results and is more
easily implemented in software.
Inputs: Plaintext, n 64-bit values {P1, P2, ..., Pn}, and
Key, K (the KEK).
Outputs: Ciphertext, (n+1) 64-bit values {C0, C1, ..., Cn}.
1) Initialize variables.
Set A = IV, an initial value (see Section 3.4)
For i = 1 to n
R[i] = P[i]
2) Calculate intermediate values.
For j = 0 to 5
For i=1 to n
B = Camellia(K, A | R[i])
A = MSB(64, B) ^ t where t = (n*j)+i
R[i] = LSB(64, B)
3) Output the results.
Set C[0] = A
For i = 1 to n
C[i] = R[i]
3.3 Camellia Key Unwrap
Key unwrapping with Camellia is identical to Section 2.2.2 of
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[RFC3394], with "AES" replaced by "Camellia".
The inputs to the unwrap process are the KEK and (n+1) 64-bit blocks
of ciphertext consisting of previously wrapped key. It returns n
blocks of plaintext consisting of the n 64-bit blocks of the
decrypted key data.
Inputs: Ciphertext, (n+1) 64-bit values {C0, C1, ..., Cn}, and
Key, K (the KEK).
Outputs: Plaintext, n 64-bit values {P1, P2, ..., Pn}.
1) Initialize variables.
Set A[s] = C[0] where s = 6n
For i = 1 to n
R[s][i] = C[i]
2) Calculate the intermediate values.
For t = s to 1
A[t-1] = MSB(64, Camellia-1(K, ((A[t] ^ t) | R[t][n]))
R[t-1][1] = LSB(64, Camellia-1(K, ((A[t]^t) | R[t][n]))
For i = 2 to n
R[t-1][i] = R[t][i-1]
3) Output the results.
If A[0] is an appropriate initial value (see Section 3.4),
Then
For i = 1 to n
P[i] = R[0][i]
Else
Return an error
The unwrap algorithm can also be specified as an index based
operation, allowing the calculations to be carried out in place.
Again, this produces the same results as the register shifting
approach.
Inputs: Ciphertext, (n+1) 64-bit values {C0, C1, ..., Cn}, and
Key, K (the KEK).
Outputs: Plaintext, n 64-bit values {P0, P1, K, Pn}.
1) Initialize variables.
Set A = C[0]
For i = 1 to n
R[i] = C[i]
2) Compute intermediate values.
For j = 5 to 0
For i = n to 1
B = Camellia-1(K, (A ^ t) | R[i]) where t = n*j+i
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A = MSB(64, B)
R[i] = LSB(64, B)
3) Output results.
If A is an appropriate initial value (see Section 3.4),
Then
For i = 1 to n
P[i] = R[i]
Else
Return an error
3.4 Key Data Integrity -- the Initial Value
The initial value (IV) refers to the value assigned to A[0] in the
first step of the wrapping process. This value is used to obtain an
integrity check on the key data. In the final step of the
unwrapping process, the recovered value of A[0] is compared to the
expected value of A[0]. If there is a match, the key is accepted as
valid, and the unwrapping algorithm returns it. If there is not a
match, then the key is rejected, and the unwrapping algorithm
returns an error.
The exact properties achieved by this integrity check depend on the
definition of the initial value. Different applications may call
for somewhat different properties; for example, whether there is
need to determine the integrity of key data throughout its lifecycle
or just when it is unwrapped. This specification defines a default
initial value that supports integrity of the key data during the
period it is wrapped (in Section 3.4.1). Provision is also made to
support alternative initial values (in Section 3.4.2).
3.4.1 Default Initial Value
The default initial value (IV) is defined to be the hexadecimal
constant:
A[0] = IV = A6A6A6A6A6A6A6A6
The use of a constant as the IV supports a strong integrity check on
the key data during the period that it is wrapped. If unwrapping
produces A[0] = A6A6A6A6A6A6A6A6, then the chance that the key data
is corrupt is 2^-64. If unwrapping produces A[0] any other value,
then the unwrap must return an error and not return any key data.
3.4.2 Alternative Initial Values
When the key wrap is used as part of a larger key management
protocol or system, the desired scope for data integrity may be more
than just the key data or the desired duration for more than just
the period that it is wrapped. Also, if the key data is not just an
Camellia key, it may not always be a multiple of 64 bits.
Alternative definitions of the initial value can be used to address
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such problems. According to [RFC3394], NIST will define alternative
initial values in future key management publications as needed. In
order to accommodate a set of alternatives that may evolve over
time, key wrap implementations that are not application-specific
will require some flexibility in the way that the initial value is
set and tested.
4. SMIMECapabilities Attribute
An S/MIME client SHOULD announce the set of cryptographic functions
it supports by using the S/MIME capabilities attribute. This
attribute provides a partial list of OIDs of cryptographic functions
and MUST be signed by the client. The functions' OIDs SHOULD be
logically separated in functional categories and MUST be ordered
with respect to their preference.
RFC 2633 [RFC2633], Section 2.5.2 defines the SMIMECapabilities
signed attribute (defined as a SEQUENCE of SMIMECapability
SEQUENCEs) to be used to specify a partial list of algorithms that
the software announcing the SMIMECapabilities can support.
If an S/MIME client is required to support symmetric encryption with
Camellia, the capabilities attribute MUST contain the Camellia OID
specified above in the category of symmetric algorithms. The
parameter associated with this OID MUST be CamelliaSMimeCapability.
CamelliaSMimeCapabilty ::= NULL
The SMIMECapability SEQUENCE representing Camellia MUST be
DER-encoded as the following hexadecimal strings:
Key Size Capability
128 30 0f 06 0b 2a 83 08 8c 9a 4b 3d 01 01 01 02 05 00
196 30 0f 06 0b 2a 83 08 8c 9a 4b 3d 01 01 01 03 05 00
256 30 0f 06 0b 2a 83 08 8c 9a 4b 3d 01 01 01 04 05 00
When a sending agent creates an encrypted message, it has to decide
which type of encryption algorithm to use. In general the decision
process involves information obtained from the capabilities lists
included in messages received from the recipient, as well as other
information such as private agreements, user preferences, legal
restrictions, and so on. If users require Camellia for symmetric
encryption, it MUST be supported by the S/MIME clients on both the
sending and receiving side, and it MUST be set in the user
preferences.
5. Security Considerations
This document specifies the use of Camellia for encrypting the
content of a CMS message and for encrypting the symmetric key used
to encrypt the content of a CMS message, and the other mechanisms
are the same as the existing ones. Therefore, the security
considerations described in the CMS specifications [CMS][CMSALG] and
the AES key wrap algorithm [AES-WRAP][RFC3394] can be applied to
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this document. No security problem has been found on Camellia
[CRYPTREC][NESSIE].
6. Intellectual Property Statement
Mitsubishi Electric Corporation and Nippon Telegraph and Telephone
Corporation have pending applications or filed patents which are
essential to Camellia. License policy for these essential patents
will be available on the IETF page of Intellectual Property Rights
Notices.
References
[AES] National Institute of Standards.
FIPS Pub 197: Advanced Encryption Standard (AES). 26
November 2001.
[DES] National Institute of Standards and Technology.
FIPS Pub 46: Data Encryption Standard. 15 January 1977.
[AES-WRAP] National Institute of Standards and Technology. AES Key
Wrap Specification. 17 November 2001.
http://csrc.nist.gov/encryption/kms/key-wrap.pdf
[CamelliaID] J. Nakajima and S. Moriai, "A Description of the
Camellia Encryption Algorithm", Internet-Draft, July 2001.
draft-nakajima-camellia-02.txt
[CamelliaSpec] K. Aoki, T. Ichikawa, M. Kanda, M. Matsui, S. Moriai,
J. Nakajima, and T. Tokita "Specification of Camellia - a
128-bit Block Cipher". http://info.isl.ntt.co.jp/camellia/
[CamelliaTech] K. Aoki, T. Ichikawa, M. Kanda, M. Matsui, S. Moriai,
J. Nakajima, and T. Tokita "Camellia: A 128-Bit Block Cipher
Suitable for Multiple Platforms - Design and Analysis -", In
Selected Areas in Cryptography, 7th Annual International
Workshop, SAC 2000, August 2000, Proceedings, Lecture Notes in
Computer Science 2012, pp.39--56, Springer-Verlag, 2001.
[CMS] R. Housley, "Cryptographic Message Syntax", RFC 3369, August
2002.
[CMSALG] R. Housley, "Cryptographic Message Syntax (CMS)
Algorithms", RFC 3370, August 2002.
[CRYPTREC] Information-technology Promotion Agency (IPA), Japan,
CRYPTREC. http://www.ipa.go.jp/security/enc/CRYPTREC/index-e.html
[NESSIE] New European Schemes for Signatures, Integrity and
Encryption (NESSIE) project. http://www.cryptonessie.org
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC2633] Ramsdell, B., Editor. S/MIME Version 3 Message
Specification. RFC 2633. June 1999.
[RFC3394] J. Schaad and R. Housley, "Advanced Encryption Standard
(AES) Key Wrap Algorithm", RFC 3394, September 2002.
Authors' Address
Shiho Moriai
Nippon Telegraph and Telephone Corporation
Phone: +81-468-59-2007
FAX: +81-468-59-3858
Email: shiho@isl.ntt.co.jp
Akihiro Kato
NTT Software Corporation
Phone: +81-45-212-7404
FAX: +81-45-212-7410
Email: akato@po.ntts.co.jp
Appendix A ASN.1 Module
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- Camellia using CBC-chaining mode for key sizes of 128, 192, 256
id-camellia128-cbc OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) 392 200011 61 security(1)
algorithm(1) symmetric-encryption-algorithm(1)
camellia128-cbc(2) }
id-camellia192-cbc OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) 392 200011 61 security(1)
algorithm(1) symmetric-encryption-algorithm(1)
camellia192-cbc(3) }
id-camellia256-cbc OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) 392 200011 61 security(1)
algorithm(1) symmetric-encryption-algorithm(1)
camellia256-cbc(4) }
-- Camellia-IV is a the parameter for all the above object identifiers.
Camellia-IV ::= OCTET STRING (SIZE(16))
-- Camellia S/MIME Capabilty parameter for all the above object
-- identifiers.
CamelliaSMimeCapability ::= NULL
-- Camellia Key Wrap Algorithm identifiers - Parameter is absent
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id-camellia128-wrap OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) 392 200011 61 security(1)
algorithm(1) key-wrap-algorithm(3)
camellia128-wrap(2) }
id-camellia192-wrap OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) 392 200011 61 security(1)
algorithm(1) key-wrap-algorithm(3)
camellia192-wrap(3) }
id-camellia256-wrap OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) 392 200011 61 security(1)
algorithm(1) key-wrap-algorithm(3)
camellia256-wrap(4) }
END
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