INTERNET-DRAFT Donald D. Eastlake 3rd
Motorola
Expires: July 2002 January 2002.
Additional XML Security URIs
---------- --- -------- ----
<draft-eastlake-xmldsig-uri-02.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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The list of current Internet-Drafts can be accessed at
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Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
A number of algorithm and keying information identifying URIs
intended for use with XML Digital Signatures and XML Encryption 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. Algorithm URIs..........................................3
2.1 DigestMethod Algorithms................................4
2.1.1 MD5..................................................4
2.1.2 SHA-384..............................................4
2.2 SignatureMethod Message Authentication Code Algorithms.4
2.2.1 HMAC-MD5.............................................5
2.2.2 HMAC SHA Variations..................................5
2.2.3 HMAC-RIPEMD160.......................................6
2.3 SignatureMethod Public Key Signature Algorithms........6
2.3.1 RSA-MD5..............................................6
2.3.2 RSA-SHA256...........................................7
2.3.3 RSA-SHA384...........................................7
2.3.4 RSA-SHA512...........................................8
2.3.5......................................................8
2.4 Minimal Canonicalization...............................8
2.5 Transform Algorithms...................................8
2.5.1 XPointer.............................................9
2.6 ARCFOUR Encryption Algorithm...........................9
3. KeyInfo................................................10
3.1 PKCS #7 Bag of Certificates and CRLs..................10
3.2 Additional RetrievalMethod Type Values................10
4. IANA Considerations....................................10
5. Security Considerations................................11
References................................................12
Author's Address..........................................13
Expiration and File Name..................................13
Full Copyright Statement..................................14
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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] and a Draft Standard version is pending before the IESG
[XMLDSIG-D]. Canonical XML, which is used by many digital
signatures, has been standardized by the W3C and is documented in
Informational [RFC 3076]. In addition, XML Encryption [XMLENC] and
Exclusive XML Canonicalization [Exclusive] are currently being
standardized by the W3C.
All of these standards and recommendations use URIs to identify
algorithms and keying information types. This document is intended
to be a convenient reference list of URIs and descriptions for
algorithms in which there is substantial interest but which can not
or have not been included in the main documents for some reason. Note
in particular that raising XML digital signature to Draft Standard in
the IETF requires remove of any algorithms for which there is not
demonstrated interoperability from the main standards document. This
requires removal of the Minimal Canonicalization algorithm, in which
there appears to be continued interest, to be dropped from the
standards track specification. It is included here.
2. Algorithm URIs
The URI being dropped from the standard due to the transition from
Proposed Standard to Draft Stanard is included herein with its
original
http://www.w3.org/2000/09/xmldsig#
prefix so as to avoid changing the XMLDSIG standard's namespace.
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
as are some URIs from the on-going XML Encryption standardization
effort. An "xmldsig-more" URI does not imply any official W3C status
for these algorithms or identifiers. Currently, dereferencing such
URIs may produce a temporary placeholder document. Permission to use
these URIs has been given by the W3C.
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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:
<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-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. Because it takes roughly the same amount of
effort to compute a SHA-384 message digest as a SHA-512 digest and
terseness is usually not a criteria in XML application, use of SHA-
512 as an alternative is recommended.
2.2 SignatureMethod Message Authentication Code Algorithms
Some text in this section is duplicated from RFC 3075 for the
convenience of the reader.
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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>
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 Variations
Identifiers:
http://www.w3.org/2001/04/xmldsig-more#hmac-sha256
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http://www.w3.org/2001/04/xmldsig-more#hmac-sha384
http://www.w3.org/2001/04/xmldsig-more#hmac-sha512
SHA-256, SHA-384, and SHA-512 [SHA-256] can also be used in HMAC as
described in section 2.2.1 above for HMAC-MD5.
2.2.3 HMAC-RIPEMD160
Identifier:
http://www.w3.org/2001/04/xmldsig-more#hmac-ripemd160
RIPEMD-160 [RIPEMD-160] can also be used in HMAC as described in
section 2.2.1 above for HMAC-MD5.
2.3 SignatureMethod Public Key Signature Algorithms
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:
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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.
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"
/>
Because it takes about the same effort to calculate a SHA-384 message
digest as it does a SHA-512 message digest, it is recommended that
RSA-SHA512 be used in preference to RSA-SHA384 where possible.
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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"
/>
2.3.5
Identifier:
http://www.w3.org/2001/04/xmldsig-more/rsa-ripemd160
This siganture method uses PKCS#1 padding as described in section
2.3.1. An example of use is
<SignatureMethod
Algorithm="http://www.w3.org/2001/04/xmldsig-more/rsa-ripemd160"
/>
2.4 Minimal Canonicalization
At this time two independent interoperable implementations of Minimal
Canonicalization have not been announced. Therefore, when XML
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.
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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:
<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.
2.6 ARCFOUR Encryption Algorithm
Identifier:
http://www.w3.org/2001/04/xmldsgi-more#arcfour
ARCFOUR is a fast, simple stream encryption algorithm that is
compatible with RSA Security's RC4 algorithm. An example
EncryptionMethod element using ARCFOUR is
<EncryptionMethod
Algorithm="http://www.w3.org/2001/04/xmldsgi-more#arcfour">
<KeySize>40</KeySize>
</EncryptionMethod>
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3. KeyInfo
In section 3.1 below a new KeyInfo element child is specified while
in section 3.2 additional KeyInfo Type values for use in
RetrievalMethod are specified.
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 (CRLs). The
PKCS7signedData element is defined to accomodate such structures
within KeyInfo. The binary PKCS #7 strucuture is base64 [RFC 2405]
encoded. Any signer information present is ignored. The following
is a example, elliding the base64 data:
<foo:PKCS7signedData
xmlns:foo="http://www.w3.org/2001/04/xmldsig-more">
...
</foo:PKCS7signedData>
3.2 Additional RetrievalMethod Type Values
The Type attribute of RetrievalMethod is an optional identifier for
the type of data to be retrieved. The result of de-referencing a
RetrievalMethod reference for all KeyInfo types with an XML structure
is an XML element or document with that element as the root. The
various "raw" key information types return a binary value. Thus they
require a Type attibute because they are not unambiguously parseable.
Identifiers:
http://www.w3.org/2000/09/xmldsig-more#KeyValue
http://www.w3.org/2000/09/xmldsig-more#RetrievalMethod
http://www.w3.org/2000/09/xmldsig-more#KeyName
http://www.w3.org/2000/09/xmldsig-more#rawX509CRL
http://www.w3.org/2000/09/xmldsig-more#rawPGPKeyPacket
http://www.w3.org/2000/09/xmldsig-more#rawSPKISexp
http://www.w3.org/2000/09/xmldsig-more#PKCS7signedData
http://www.w3.org/2000/09/xmldsig-more#rawPKCS7signedData
4. IANA Considerations
None. (so far)
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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
[Exclusive] - Exclusive XML Canonicalization Version 1.0, D.
Eastlake, J. Reagle, 18 October 2001.
<http://www.w3.org/Signature/Drafts/xml-exc-c14n.html>
[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.
[RIPEMD-160] - ISO/IEC 10118-3:1998, Information Technology -
Security techniques - Hash-functions - Part3: Dedicated hash-
functions, ISO, 1998.
[SHA-384] - US Federal Information Processing Standard 180-2, Secure
Hash Standard, Draft.
[XMLDSIG-D] - XML - Signature Syntax and Processing, D. Eastlake, J.
Reagle, D. Solo, August 2001. <http://www.w3.org/TR/2001/PR-xmldsig-
core-20010820/> and corresponding internet-draft.
[XMLENC] - XML Encryption Syntax and Processing, J. Reagle, D.
Eastlake, October 2001. <http://www.w3.org/TR/2001/WD-xmlenc-core-
20011018/>
[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)
+1-508-851-8280 (w)
FAX: +1-508-851-8507 (w)
EMail: Donald.Eastlake@motorola.com
Expiration and File Name
This draft expires July 2002.
Its file name is draft-eastlake-xmldsig-uri-02.txt.
D. Eastlake 3rd [Page 13]
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Full Copyright Statement
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D. Eastlake 3rd [Page 14]