INTERNET-DRAFT Donald Eastlake 3rd
Motorola
Expires: October 2001 April 2001
Additional XML Digital Signature URIs
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<draft-eastlake-xmldsig-uri-01.txt>
Status of This Document
Distribution of this draft is unlimited. It is intended to become an
Informational RFC and will probably also be published as a W3C Note.
Comments should be sent to the author or the XMLDSIG working group
<w3c-ietf-xmldsig@w3.org>.
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026. Internet-Drafts are
working documents of the Internet Engineering Task Force (IETF), its
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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The list of current Internet-Drafts can be accessed at
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Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
A number of algorithm URIs intended for use with XML Digital
Signatures [RFC 3075] are defined.
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Acknowledgements
Glenn Adams, Merlin Hughs, Brian LaMachia, Joseph Reagle
Table of Contents
Status of This Document....................................1
Copyright Notice...........................................1
Abstract...................................................1
Acknowledgements...........................................2
Table of Contents..........................................2
1. Introduction............................................3
2. URIs....................................................3
2.1 DigestMethod Algorithms................................3
2.1.1 MD5..................................................3
2.1.2 SHA-256..............................................4
2.1.3 SHA-384..............................................4
2.1.4 SHA-512..............................................4
2.2 SignatureMethod Message Authentication Code Algorithms.5
2.2.1 HMAC-MD5.............................................5
2.2.2 HMAC-SHA-256.........................................6
2.2.3 HMAC-SHA-384.........................................6
2.2.4 HMAC-SHA-512.........................................6
2.3 SignatureMethod Public Key Signature Algorithms........6
2.3.1 RSA-MD5..............................................7
2.3.2 RSA-SHA256...........................................8
2.3.3 RSA-SHA384...........................................8
2.3.4 RSA-SHA512...........................................8
2.4 CanonicalizatonMethod Algorithms.......................8
2.4.1 Minimal Canonicalization.............................8
2.5 Transform Algorithms...................................9
2.5.1 XPointer.............................................9
3. KeyInfo Elements.......................................10
3.1 PKCS #7 Bag of Certificates and CRLs..................10
4. IANA Considerations....................................10
5. Security Considerations................................10
References................................................11
Author's Address..........................................12
Expiration and File Name..................................12
Full Copyright Statement..................................13
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1. Introduction
XML Digital Signatures have been standardized by the joint IETF/W3C
XMLDSIG working group. The Proposed Standard is specified in [RFC
3075]. In addition, Canonical XML, which is used by many digital
signatures, has been standardized by the W3C and is documented in
Informational [RFC 3076].
[RFC 3075] specifies URIs to identify algorithms. However, this
protocol is likely to be raised to Draft Standard soon, which
requires two independent interoperable implementations to exist.
This may require algorithms in which there appears to be continued
interest to be dropped from the standards track specification. This
document is intended as a convenient reference list of URIs and
descriptions for any dropped from the Proposed Standard due to lack
of implementations plus additional suggested algorithms in which
there appears to be substantial interest.
2. URIs
The sections below parallel those in Section 6 of RFC 3075 which
group various algorithms by their use in XML Digital Sigantures.
URIs being dropped from the standard due to the transition from
Proposed Standard to Draft Stanard are included herein. Additional
non-proprietary algorithms, particularly those based on USA
Government and W3C standards, are given URIs that start with
http://www.w3.org/2001/04/xmldsig-more
This does not imply any official W3C status for these algorithms.
Currently, dereferencing such URIs produces, at best, a temporary
placeholder document. Permission to use these URIs was tentatively
given by W3C staff.
2.1 DigestMethod Algorithms
2.1.1 MD5
Identifier:
http://www.w3.org/2001/04/xmldsig-more#md5
The MD5 algorithm [RFC 1321] takes no explicit parameters. An example
of an MD5 DigestAlgorithm element is:
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<DigestMethod
Algorithm="http://www.w3.org/2001/04/xmldsig-more#md5"/>
An MD5 digest is a 128-bit string. The content of the DigestValue
element shall be the base64 [RFC 2045] encoding of this bit string
viewed as a 16-octet octet stream.
2.1.2 SHA-256
Identifier:
http://www.w3.org/2001/04/xmldsig-more#sha256
The SHA-256 algorithm [SHA-256] takes no explicit parameters. An
example of a SHA-256 DigestAlgorithm element is:
<DigestMethod
Algorithm="http://www.w3.org/2001/04/xmldsig-more#sha256/>
A SHA-256 disgest is a 256 bit string. The content of the
DigestValue element shall be the base64 [RFC 2045] encoding of this
string viewed as a 32-octet stream.
2.1.3 SHA-384
Identifier:
http://www.w3.org/2001/04/xmldsig-more#sha384
The SHA-384 algorithm [SHA-384] takes no explicit parameters. An
example of a SHA-384 DigestAlforithm element is:
<DigestMethod
Algorith="http://www.w3.org/2001/04/xmldsig-more#sha384"/>
A SHA-384 digest is a 384 bit string. The content of the DigestValue
element shall be the base64 [RFC2045] encoding of this string viewed
as a 48-octet stream.
2.1.4 SHA-512
Identifier:
http://www.w3.org/2001/04/xmldsig-more#sha512
The SHA-512 algorithm [SHA-512] takes an no explicit parameters. An
example of a SHA-512 DigestAlgorithm elementis:
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<DigestMethod
Algorithm="http://www.w3.org/2001/04/xmldsig-more#sha512"/>
A SHA-512 digest is a 512 bit string. The content of the DigestValue
element shall be the base64 [RFC2045] encoding of this string viewed
as a 64-octet stream.
2.2 SignatureMethod Message Authentication Code Algorithms
Some text in this section is duplicated from RFC 3075 for the
convenience of the reader.
2.2.1 HMAC-MD5
Identifier:
http://www.w3.org/2001/04/xmldsig-more#hmac-md5
The HMAC algorithm [RFC 2104] takes the truncation length in bits as
a parameter; if the parameter is not specified then all the bits of
the hash are output. An example of an HMAC-MD5 SignatureMethod
element is as follows:
<SignatureMethod
Algorithm="http://www.w3.org/2001/04/xmldsig-more#hmac-md5">
<HMACOutputLength>112</HMACOutputLength>
</SignatureMethod>
The output of the HMAC algorithm is ultimately the output (possibly
truncated) of the chosen digest algorithm. This value shall be base64
[RFC 2405] encoded in the same straightforward fashion as the output
of the digest algorithms. Example: the SignatureValue element for the
HMAC-MD5 digest
9294727A 3638BB1C 13F48EF8 158BFC9D
from the test vectors in [RFC 2104] would be
<SignatureValue>kpRyejY4uxwT9I74FYv8nQ==</SignatureValue>
Schema Definition:
<simpleType name="HMACOutputLengthType">
<restriction base="integer"/>
</simpleType>
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DTD:
<!ELEMENT HMACOutputLength (#PCDATA)>
The Schema Definition and DTD immediately above are copied from RFC
3075.
Although some cryptographic suspicions have recently been cast on MD5
for use in signatures such as RSA-MD5 below, this does not effect use
of MD5 in HMAC.
2.2.2 HMAC-SHA-256
Identifier:
http://www.w3.org/2001/04/xmldsig-more#hmac-sha256
SHA-256 [SHA-256] can also be used in HMAC as described in section
2.2.1 above for HMAC-MD5.
2.2.3 HMAC-SHA-384
Identifier:
http://www.w3.org/2001/04/xmldsig-more#hmac-sha384
SHA-384 [SHA-384] can also be used in HMAC as described in section
2.2.1 above for HMAC-MD5.
2.2.4 HMAC-SHA-512
Identifier:
http://www.w3.org/2001/04/xmldsig-more#hmac-sha512
SHA-512 [SHA-512] can also be used in HMAC as describe in section
2.2.1 above for HMAC-MD5.
2.3 SignatureMethod Public Key Signature Algorithms
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2.3.1 RSA-MD5
Identifier:
http://www.w3.org/2001/04/xmldsig-more#rsa-md5
This implies the PKCS#1 v1.5 padding algorithm described in [RFC
2437].
An example of use is
<SignatureMethod
Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-md5"/>
The SignatureValue content for an RSA-MD5 signature is the base64
[RFC 2405] encoding of the octet string computed as per [RFC 2437],
section 8.1.1.
Signature generation for the RSASSA-PKCS1-v1_5 signature scheme. As
specified in the EMSA-PKCS1-V1_5-ENCODE function in [RFC 2437,
section 9.2.1], the value input to the signature function MUST
contain a pre-pended algorithm object identifier for the hash
function, but the availability of an ASN.1 parser and recognition of
OIDs is not required of a signature verifier. The PKCS#1 v1.5
representation appears as:
CRYPT (PAD (ASN.1 (OID, DIGEST (data))))
Note that the padded ASN.1 will be of the following form:
01 | FF* | 00 | prefix | hash
where "|" is concatentation, "01", "FF", and "00" are fixed octets of
the corresponding hexadecimal value, "hash" is the MD5 digest of the
data, and "prefix" is the ASN.1 BER MD5 algorithm designator prefix
required in PKCS #1 [RFC 2437], that is,
hex 30 20 30 0c 06 08 2a 86 48 86 f7 0d 02 05 05 00 04 10
This prefix is included to make it easier to use standard
cryptographic libraries. The FF octet MUST be repeated the maximum
number of times such that the value of the quantity being CRYPTed is
one octet shorter than the RSA modulus.
Due to increases in computer processor power and advances in
cryptography, use of RSA-MD5 is NOT RECOMMENDED.
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2.3.2 RSA-SHA256
Identifier:
http://www.w3.org/2001/04/xmldsig-more#rsa-sha256
An example of use is
<SignatureMethod
Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256"
/>
[I think the SHA-256/384/512 RSA signature algorithms should use
PKCS#1 v2, i.e., OAEP.]
2.3.3 RSA-SHA384
Identifier:
http://www.w3.org/2001/04/xmldsig-more#rsa-sha384
An example of use is
<SignatureMethod
Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha384"
/>
2.3.4 RSA-SHA512
Identifier:
http://www.w3.org/2001/04/xmldsig-more#rsa-sha512
An example of use is
<SignatureMethod
Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha512"
/>
2.4 CanonicalizatonMethod Algorithms
2.4.1 Minimal Canonicalization
At this time two independent interoperable implementations of Minimal
Canonicalization have not been announced. Therefore, when XML
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Digital Siganture is advanced from Proposed Standard to Draft
Standard, it must be dropped from the standard track documents.
However, there is still interest and indicates of possible future use
for Minimal Canonicalization. For its definition, see [RFC 3075],
Section 6.5.1.
For reference, it's identifier remains:
http://www.w3.org/2000/09/xmldsig#minimal
2.5 Transform Algorithms
Note that all CanonicalizationMethod algorithms listed can also be
used as Transform algorithms.
2.5.1 XPointer
Identifier:
http://www.w3.org/2001/04/xmldsig-more/xptr
This transform algorithm takes an [XPointer] as an explicit
parameter. An example of use is [RFC 3092]:
<Transform
Algorithm="http://www.w3.org/2001/04/xmldsig-more/xptr">
<XPointer
xmlns="http://www.w3.org/2001/04/xmldsig-more/xptr">
xpointer(id("foo")) xmlns(bar=urn:baz)
xpointer(//bar:Zab[@Id="foo"])
</XPointer>
</Transform>
Schema Definition:
<element name="XPointer" type="string"/>
DTD:
<!ELEMENT XPointer (#PCDATA)>
Input to this transfrom is an octet stream (which is then parsed into
XML).
Output from this transform is a node set; the results of the XPointer
are processed as defined in the XMLDSIG specification [RFC 3075] for
a same-document XPointer.
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3. KeyInfo Elements
3.1 PKCS #7 Bag of Certificates and CRLs
A PKCS #7 [RFC 2315] "signedData" can also be used as a bag of
certificates and/or certificate revocation lists. The
PKCS7signedData element is defined to accomodate such structures
within KeyInfo. The binary PKCS #7 strucuture is base64 encoded.
Any signer information present is ignored. The following is a
example, elliding the base64 data [RFC 3092]:
<foo:PKCS7signedData
xmlns:foo="http://www.w3.org/2001/04/xmldsig-more">
...
</foo:PKCS7signedData>
4. IANA Considerations
None. (so far)
5. Security Considerations
Due to computer speed and cryptographic advances, the use of MD5 as a
DigestMethod or in the RSA-MD5 SigantureMethod is NOT RECOMMENDED.
The cryrptographic advances concerned do not effect the security of
HMAC-MD5; however, there is little reason not to go for one of the
SHA series of algorithms.
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References
[RFC 1321] - "The MD5 Message-Digest Algorithm", R. Rivest, April
1992.
[RFC 2104] - "HMAC: Keyed-Hashing for Message Authentication", H.
Krawczyk, M. Bellare, R. Canetti, February 1997.
[RFC 2405] - "Multipurpose Internet Mail Extensions (MIME) Part One:
Format of Internet Message Bodies", N. Freed, N. Borenstein, November
1996.
[RFC 2437] - "PKCS #1: RSA Cryptography Specifications Version 2.0",
B. Kaliski, J. Staddon, October 1998.
[RFC 2315] - "PKCS #7: Cryptographic Message Syntax Version 1.5", B.
Kaliski, March 1998.
[RFC 3075] - "XML-Signature Syntax and Processing", D. Eastlake, J.
Reagle, D. Solo, March 2001. <http://www.w3.org/TR/2000/CR-
xmldsig-core-20001031>
[RFC 3076] - "Canonical XML Version 1.0", J. Boyer, March 2001.
<http://www.w3.org/TR/2001/REC-xml-c14n-20010315>
[RFC 3092] - "Etymology of 'Foo'", D. Eastlake 3rd, C. Manros, E.
Raymond, 1 April 2001.
[SHA-256] -
[SHA-384] -
[SHA-512] -
[XPointer] - "XML Pointer Language (XPointer) Version 1.0", W3C
working draft, Steve DeRose, Eve Maler, Ron Daniel Jr., January 2001.
<http://www.w3.org/TR/2001/WD-xptr-20010108>
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Author's Address
Donald E. Eastlake 3rd
Motorola
155 Beaver Street
Milford, MA 01757 USA
Telephone: +1-508-634-2066 (h)
+1-508-261-5434 (w)
FAX: +1-508-261-4447 (w)
EMail: Donald.Eastlake@motorola.com
Expiration and File Name
This draft expires October 2001.
Its file name is draft-eastlake-xmldsig-uri-01.txt.
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Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved.
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