Network Working Group K. Davidson

Network Working Group K. Davidson
Request for Comments: 2802 Differential
Category: Informational Y. Kawatsura
Hitachi
April 2000

Digital Signatures for the v1.0 Internet Open Trading Protocol (IOTP)

Status of this Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2000). All Rights Reserved.

Abstract

A syntax and procedures are described for the computation and
verification of digital signatures for use within Version 1.0 of the
Internet Open Trading Protocol (IOTP).

Acknowledgment

This document is based on work originally done on general XML digital
signatures by:

Richard Brown of GlobeSet, Inc. <[email protected]>

Other contributors to the design of the IOTP DSIG DTD include, in
alphabetic order:

David Burdett, Commerce One
Andrew Drapp, Hitachi
Donald Eastlake 3rd, Motorola, Inc.

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Table of Contents

1. Introduction............................................3
2. Objective and Requirements..............................3
3. Signature Basics........................................3
3.1 Signature Element......................................3
3.2 Digest Element.........................................4
3.3 Originator and Recipient Information Elements..........5
3.4 Algorithm Element......................................5
4. Detailed Signature Syntax...............................6
4.1 Uniform Resource Names.................................6
4.2 IotpSignatures.........................................6
4.3 Signature Component....................................6
4.3.1 Signature............................................6
4.3.2 Manifest.............................................7
4.3.3 Algorithm............................................9
4.3.4 Digest...............................................9
4.3.5 Attribute...........................................10
4.3.6 OriginatorInfo......................................11
4.3.7 RecipientInfo.......................................11
4.3.8 KeyIdentifier.......................................12
4.3.9 Parameter...........................................13
4.4 Certificate Component.................................13
4.4.1 Certificate.........................................13
4.4.2 IssuerAndSerialNumber...............................14
4.5 Common Components.....................................15
4.5.1 Value...............................................15
4.5.2 Locator.............................................15
5. Supported Algorithms...................................16
5.1 Digest Algorithms.....................................16
5.1.1 SHA1................................................16
5.1.2 DOM-HASH............................................17
5.2 Signature Algorithms..................................17
5.2.1 DSA.................................................17
5.2.2 HMAC................................................18
5.2.3 RSA.................................................20
5.2.4 ECDSA...............................................20
6. Examples...............................................21
7. Signature DTD..........................................23
8. Security Considerations................................25
References................................................26
Authors' Addresses........................................28
Full Copyright Statement..................................29

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1. Introduction

The Internet Open Trading Protocol (IOTP) provides a payment system
independent interoperable framework for Internet commerce as
documented in [RFC 2801]. All IOTP messages are XML documents. XML,
the Extensible Markup Language [XML], is a syntactical standard
promulgated by the World Wide Web Consortium. XML is intended
primarily for structuring data exchanged and served over the World
Wide Web.

Although IOTP assumes that any payment system used with it provides
its own security, there are numerous cases where IOTP requires
authentication and integrity services for portions of the XML
messages it specifies.

2. Objective and Requirements

This document covers how digital signatures may be used with XML
documents to provide authentication and tamper-proof protocol
messages specifically for Version 1.0 of the IOTP protocol. The
reader should recognize that an effort towards general XML digital
signatures exists but is unlikely to produce its final result in time
for IOTP Version 1.0. Future versions of IOTP will probably adopt by
reference the results of this general XML digital signature effort.

The objective of this document is to propose syntax and procedures
for the computation and verification of digital signatures applicable
to Version 1.0 IOTP protocol messages, providing for:

-- Authentication of IOTP transactions
-- Provide a means by which an IOTP message may be made "tamper-
proof", or detection of tampering is made evident
-- Describe a set of available digest and signature algorithms at
least one of which is mandatory to implement for interoperability
-- Easily integrate within the IOTP 1.0 Specification
-- Provide lightweight signatures with minimal redundancy
-- Allow signed portions of IOTP message to be "forwarded" to another
trading roles with different signature algorithms than the
original recipient

3. Signature Basics

3.1 Signature Element

This specification consists primarily of the definition of an XML
element known as the Signature element. This element consists of two
sub-elements. The first one is a set of authenticated attributes,
known as the signature Manifest, which comprises such things as a

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unique reference to the resources being authenticated and an
indication of the keying material and algorithms being used. The
second sub-element consists of the digital signature value.

<Signature>
<Manifest>
(resource information block)
(originator information block)
(recipient information block)
(other attributes)
(signature algorithms information block)
</Manifest>
<Value encoding 'encoding scheme'>
(encoded signature value)
<Value>
</Signature>

The digital signature is not computed directly from the pieces of
information to be authenticated. Instead, the digital signature is
computed from a set of authenticated attributes (the Manifest), which
include references to, and a digests of, those pieces of information.

The authentication is therefore "indirect".

3.2 Digest Element

The Digest element consists of a unique and unambiguous reference to
the XML resources being authenticated. It is constructed of a locator
and the digest value data itself. The Digest algorithm is referred to
indirectly via a DigestAlgorithmRef, so that Digest algorithms may be
shared by multiple resources.

<Digest DigestAlgorithmRef='D.1'>
<Locator href='resource locator'/>
<Value>
(Digest value)
</Value>
</Digest>

The resource locator is implemented as a simple XML Link [XLink].
This not only provides a unique addressing scheme for internal and
external resources, but also facilitates authentication of composite
documents.

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3.3 Originator and Recipient Information Elements

The purpose of the Originator and Recipient information elements is
to provide identification and keying material for these respective
parties.

<OriginatorInfo>
(identification information block)
(keying material information block)
</OriginatorInfo>

<RecipientInfo>
(identification information block)
(keying material information block)
</RecipientInfo>

The actual content of these two elements depends on the
authentication scheme being used and the existence or non-existence
of a prior relationship between the parties. In some circumstances,
it may be quite difficult to distinguish between identification and
keying material information. A unique reference to a digital
certificate provides for both. This may also stand true for an
account number when a prior relationship exists between the parties.

The Originator information element is mandatory. Depending on the
existence or non-existence of a prior relationship with the
recipient, this block either refers to a public credential such as a
digital certificate or displays a unique identifier known by the
recipient.

The Recipient information element may be used when a document
contains multiple signature information blocks, each being intended
for a particular recipient. A unique reference in the Recipient
information block helps the recipients identify their respective
Signature information block.

The Recipient information element may also be used when determination
of the authentication key consists of a combination of keying
material provided by both parties. This would be the case, for
example, when establishing a key by means of Diffie Hellman
[Schneier] Key Exchange algorithm.

3.4 Algorithm Element

The Algorithm element is a generalized place to put any type of
algorithm used within the signed IOTP message. The Algorithm may be a
Signature algorithm or a Digest algorithm. Each algorithm contains
parameters specific to the algorithm used.

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<Algorithm type='digest' ID='12'>
(algorithm information block)
</Algorithm>

Algorithms are required to contain an ID which allows for indirect
reference to them from other places in the XML signature.

4. Detailed Signature Syntax

4.1 Uniform Resource Names

To prevent potential name conflicts in the definition of the numerous
type qualifiers considered herein, this specification uses Uniform
Resource Names [RFC 2141].

4.2 IotpSignatures

The IotpSignatures element is the top-level element in an IOTP
signature block. It consists of a collection of Signature elements,
and an optional set of Certificates.

<!ELEMENT IotpSignatures (Signature+, Certificate*) >
<!ATTLIST IotpSignatures
ID ID #IMPLIED >

Content Description

Signature: A collection of Signature elements.

Certificate: Zero or more certificates used for signing

Attributes Description

ID: Element identifier that may be used to reference the entire
Signature element from a Resource element when implementing
endorsement.

4.3 Signature Component

4.3.1 Signature

The Signature element constitutes the majority of this specification.
It is comprised of two sub-elements. The first one is a set of
attributes, known as the Manifest, which actually constitutes the
authenticated part of the document. The second sub-element consists
of the signature value or values.

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The Value element contained within the Signature element is the
encoded form of the signature of the Manifest element, and thus
provides the verification of the Manifest.

The process for generating the signed value is a multi-step process,
involving a canonicalization algorithm, a digest algorithm, and a
signature algorithm.

First, the Manifest is canonicalized with an algorithm specified
within the Algorithm element of the Manifest. The canonicalized form
removes any inconsistencies in white space introduced by XML parsing
engines.

This canonicalized form is then converted into a digest form which
uniquely identifies the canonicalized document. Any slight
modification in the original document will result in a very different
digest value.

Finally, the digest is then signed using a public/symmetric key
algorithm which digitally stamps the digest (with the certificate of
the signer if available). The final signed digest is the value which
is stored within the Signature's Value element.

<!ELEMENT Signature (Manifest, Value+) >
<!ATTLIST Signature
ID ID #IMPLIED >

Content Description

Manifest: A set of attributes that actually constitutes the
authenticated part of the document.

Value: One or more encodings of signature values. Multiple values
allow for a multiple algorithms to be supported within a single
signature component.

Attributes Description

ID: Element identifier that may be used to reference the Signature
element from a Resource element when implementing endorsement.

4.3.2 Manifest

The Manifest element consists of a collection of attributes that
specify such things as references to the resources being
authenticated and an indication of the keying material and algorithms
to be used.

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<!ELEMENT Manifest
( Algorithm+,
Digest+,
Attribute*,
OriginatorInfo,
RecipientInfo+,
)
<!ATTLIST Manifest
LocatorHRefBase CDATA #IMPLIED
>

Content Description

Algorithm: A list of algorithms used for signing, digest computation,
and canonicalization.

Digest: A list of digests of resources to be authentication and
signed.

Attribute: Optional element that consists of a collection of
complementary attributes to be authenticated.

OriginatorInfo: Element that provides identification and keying
material information related to the originator.

RecipientInfo: Optional element that provides identification and
keying material information related to the recipient.

Attributes Description

LocatorHrefBase: The LocatorHrefBase provides a similar construct to
the HTML HREFBASE attribute and implicitly sets all relative URL
references within the Manifest to be relative to the HrefBase. For
example, the IOTP Manifest may contain:

<Manifest LocatorHrefBase='iotp:<globally-unique-tid>'>

And subsequent Locators may be:

<Locator href='C.9'>

An implementation should concatenate the two locator references with
"#" to create the entire URL. See definition of the Locator attribute
on the Digest element for more detail.

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4.3.3 Algorithm

This specification uses an Algorithm data type which indicates many
different types of algoirithms. The Algorithm element allows for
specification of sub-algorithms as parameters of the primary
algorithm. This is performed via a parameter within the algorithm
that provides a reference to another Algorithm. An example of this is
shown in the Parameter section.

<!ELEMENT Algorithm (Parameter*) >
<!ATTLIST Algorithm
ID ID #REQUIRED
type (digest|signature) #IMPLIED
name NMTOKEN #REQUIRED >

Content Description

Parameter: The contents of an Algorithm element consists of an
optional collection of Parameter elements which are specified on a
per algorithm basis.

Attributes Description

ID: The ID of the algorithm is used by the Digest and RecipientInfo
to refer to the signing or digest algorithm used.

type: The type of algorithm, either a digest or signature. This is
implied by the element to which the algorithm is referred. That is,
if the DigestAlgorithmRef refers to an algorithm, it is implicit by
reference that the targeted algorithm is a digest.

name: The type of the algorithm expressed as a Uniform Resource
Name.

4.3.4 Digest

The Digest element consists of the fingerprint of a given resource.
This element is constructed of two sub-elements. This first one
indicates the algorithm to be used for computation of the
fingerprint. The second element consists of the fingerprint value.

<!ELEMENT Digest (Locator, Value) >
<!ATTLIST Digest
DigestAlgorithmRef IDREF #REQUIRED
>

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Content Description

Locator: Contains a "HREF" or URL Locator for the resources to be
fingerprinted. For use within IOTP a "scheme" with the value "iotp"
may be used with the following structure:

'iotp:<globally-unique-tid>#<id-value>'.

This should be interpreted as referring to an element with an ID
attribute that matches <id-value> in any IOTP Message that has a
TransRefBlk Block with an IotpTransId that matches <globally-unique-
tid>.

If the LocatorHrefBase attribute is set on the Manifest element of
which this Digest element is a child, then concatenate the value of
the LocatorHrefBase attribute with the value of the Locator attribute
before identifying the element that is being referred to.

If the LocatorHrefBase attribute is omitted, <globally-unique-tid>
should be interpreted as the current IotpTransId, which is included
in the IOTP message which contains the Manifest component.

Value: Encoding of the fingerprint value.

Attributes Description

DigestAlgorithmRef: ID Reference of algorithm used for computation of
the digest.

4.3.5 Attribute

The Attribute element consists of a complementary piece of
information, which shall be included in the authenticated part of the
document. This element has been defined primarily for enabling some
level of customization in the signature element. This is the area
where a specific IOTP implementation may include custom attributes
which must be authenticated directly. An Attribute element consists
of a value, a type, and a criticality.

At this time, no IOTP specific attributes are specified.

<!ELEMENT Attribute ANY >
<!ATTLIST Attribute
type NMTOKEN #REQUIRED
critical ( true | false ) #REQUIRED
>

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Content Description

ANY: The actual value of an attribute depends solely upon its type.

Attributes Description

type: Type of the attribute.

critical: Boolean value that indicates if the attribute is critical
(true) or not (false). A recipient shall reject a signature that
contains a critical attribute that he does not recognize. However, an
unrecognized non-critical attribute may be ignored.

4.3.6 OriginatorInfo

The OriginatorInfo element is used for providing identification and
keying material information for the originator.

<!ELEMENT OriginatorInfo ANY >
<!ATTLIST OriginatorInfo
OriginatorRef NMTOKEN #IMPLIED
>

Content Description

ANY: Identification and keying material information may consist of
ANY construct. Such a definition allows the adoption of
application-specific schemes.

Attributes Description

OriginatorRef: A reference to the IOTP Org ID of the originating
signer.

4.3.7 RecipientInfo

The RecipientInfo element is used for providing identification and
keying material information for the recipient. This element is used
either for enabling recognition of a Signature element by a given
recipient or when determination of the authentication key consists of
the combination of keying material provided by both the recipient and
the originator.

The RecipientInfo attributes provide a centralized location where
signatures, algorithms, and certificates intended for a particular
recipient are specified.

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The signature certificate reference ID MUST point to a certificate
object.

<!ELEMENT RecipientInfo ANY >
<!ATTLIST RecipientInfo
SignatureAlgorithmRef IDREF #REQUIRED
SignatureValueRef IDREF #IMPLIED
SignatureCertRef IDREF #IMPLIED
RecipientRefs NMTOKENS #IMPLIED
>

Content Description

ANY: Identification and keying material information may consist of
ANY construct.

Attributes Description

SignatureAlgorithmRef: A reference to the signature algorithm used to
sign the SignatureValueRef intended for this recipient. The signature
algorithm reference ID MUST point to a signature algorithm within the
Manifest.

SignatureValueRef: A reference to the signature value for this
recipient. The signature value reference ID MUST point to a value
structure directly included within a Manifest. This reference can be
omitted if the application can specify the digest value.

SignatureCertRef: A reference to the certificate used to sign the
Value pointed to by the SignatureValueRef. This reference can be
omitted if the application can identify the certificate.

RecipientRefs: A list of references to the IOTP Org ID of the
recipients this signature is intended for.

4.3.8 KeyIdentifier

The key identifier element can identify the shared public/symmetric
key identification between parties that benefit from a prior
relationship. This element can be included in the ReceipientInfo
Element.

<!ELEMENT KeyIdentifier EMPTY>
<!ATTLIST KeyIdentifier
value CDATA #REQUIRED
>

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4.3.9 Parameter

A Parameter element provides the value of a particular algorithm
parameter, whose name and format have been specified for the
algorithm considered.

<!ELEMENT Parameter ANY >
<!ATTLIST Parameter
type CDATA #REQUIRED
>

For IOTP 1.0, the following parameter type is standardized:
"AlgorithmRef".

An AlgorithmRef contains an ID of a "sub-Algorithm" used when
computing a sequence of algorithms. For example, a signature
algorithm actually signs a digest algorithm. To specify a chain of
algorithms used to compute a signature, AlgorithmRef parameter types
are used in the following manner:

<Algorithm ID='A1' type='digest' name='urn:ibm-com:dom-hash'>
<Parameter type='AlgorithmRef'>A2</Parameter>
</Algorithm>
<Algorithm ID='A2' type='digest' name='urn:nist-gov:sha1'>
</Algorithm>
<Algorithm ID='A3' type='signature' name='urn:rsasdi-com:rsa-encryption'>
<Parameter type='AlgorithmRef'>A1</Parameter>
</Algorithm>

Content Description

ANY: The contents of a Parameter element consists of ANY valid
construct, which is specified on a per algorithm per parameter basis.

Attributes Description

type: The type of the parameter expressed as a free form string,
whose value is specified on a per algorithm basis.

4.4 Certificate Component

4.4.1 Certificate

The Certificate element may be used for either providing the value of
a digital certificate or specifying a location from where it may be
retrieved.

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<!ELEMENT Certificate
( IssuerAndSerialNumber,
( Value | Locator ) )
>
<!ATTLIST Certificate
ID ID #IMPLIED
type NMTOKEN #REQUIRED >

Content Description

IssuerAndSerialNumber: Unique identifier of this certificate. This
element has been made mandatory is order to prevent unnecessary
decoding during validation of a certificate chain. This feature also
helps certificates caching, especially when the value is not directly
provided.

Value: Encoding of the certificate value. The actual value to be
encoded depends upon the type of the certificate.

Locator: XML link element that could be used for retrieving a copy of
the digital certificate. The actual value being returned by means of
this locator depends upon the security protocol being used.

Attributes Description

ID: Element identifier that may be used to reference the Certificate
element from a RecipientInfo element.

type: Type of the digital certificate. This attribute is specified as
a Universal Resource Name. Support for the X.509 version 3
certificate [X.509] is mandatory in this specification if the
Certificate element is used. The URN for such certificates is
"urn:X500:X509v3".

4.4.2 IssuerAndSerialNumber

The IssuerAndSerialNumber element identifies a certificate, and
thereby an entity and a public key, by the name of the certificate
issuer and an issuer-specific certificate identification.

<!ELEMENT IssuerAndSerialNumber EMPTY >
<!ATTLIST IssuerAndSerialNumber
issuer CDATA #REQUIRED
number CDATA #REQUIRED >

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Attributes Description

issuer: Name of the issuing certification authority. See [RFC 2253]
for RECOMMENDED syntax.

number: Issuer-specific certificate identification.

4.5 Common Components

4.5.1 Value

A value contains the "raw" data of a signature or digest algorithm,
usually in a base-64 encoded form. See [RFC 2045] for algorithm used
to base-64 encode data.

<!ELEMENT Value ( #PCDATA ) >
<!ATTLIST Value
ID ID #IMPLIED
encoding (base64|none) 'base64'
>

Content Description

PCDATA: Content value after adequate encoding.

Attributes Description

encoding: This attribute specifies the decoding scheme to be
employed for recovering the original byte stream from the content of
the element. This document recognizes the following two schemes:

none: the content has not been subject to any particular encoding.
This does not preclude however the use of native XML encoding such as
CDATA section or XML escaping.

base64: The content has been encoded by means of the base64 encoding
scheme.

4.5.2 Locator

The Locator element consists of simple XML link [XLink]. This
element allows unambiguous reference to a resource or fragment of a
resource.

<!ELEMENT Locator EMPTY>
<!ATTLIST Locator
xml:link CDATA #FIXED 'simple'
href CDATA #REQUIRED >

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Attributes Description

xml:link: Required XML link attribute that specifies the nature of
the link (simple in this case).

href: Locator value that may contains either a URI [RFC 2396], a
fragment identifier, or both.

5. Supported Algorithms

The IOTP specification 1.0 requires the implementation of the DSA,
DOM-HASH, SHA1, HMAC algorithms. Implementation of RSA is also
recommended.

5.1 Digest Algorithms

This specification contemplates two types of digest algorithms, both
of which provide a digest string as a result:

Surface string digest algorithms

These algorithms do not have any particular knowledge about the
content being digested and operate on the raw content value. Any
changes in the surface string of a given content affect directly the
value of the digest being produced.

Canonical digest algorithms

These algorithms have been tailored for a particular content type and
produce a digest value that depends upon the core semantics of such
content. Changes limited to the surface string of a given content do
not affect the value of the digest being produced unless they affect
the core semantic.

5.1.1 SHA1

Surface string digest algorithm designed by NIST and NSA for use with
the Digital Signature Standard. This algorithm produces a 160-bit
hash value. This algorithm is documented in NIST FIPS Publication
180-1 [SHA1].

This algorithm does not require any parameter.

The SHA1 URN used for this specification is "urn:nist-gov:sha1".

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5.1.2 DOM-HASH

XML canonical digest algorithm proposed by IBM Tokyo Research
Laboratory. This algorithm operates on the DOM representation of the
document and provides an unambiguous means for recursive computation
of the hash value of the nodes that constitute the DOM tree [RFC
2803]. This algorithm has many applications such as computation of
digital signature and synchronization of DOM trees. However, because
the hash value of an element is computed from the hash values of the
inner elements, this algorithm is better adapted to small documents
that do not require one-pass processing.

As of today, this algorithm is limited to the contents of an XML
document and, therefore, does not provide for authentication of the
internal or external subset of the DTD.

The DOM-HASH algorithm requires a single parameter, which shall
include a surface string digest algorithm such as SHA1.

The DOM-HASH URN used for this specification is "urn:ibm-com:dom-
hash".

The DOM-HASH uses a surface-string digest algorithm for computation
of a fingerprint. The SHA1 is recommended in this specification.

Example
<Algorithm name='urn:fips:sha1' type='digest' ID='P.3'>
</Algorithm>

<Algorithm name='urn:ibm:dom-hash' type='digest' ID='P.5'>
<Parameter type='AlgorithmRef'>P.3</Parameter>
</Algorithm>

5.2 Signature Algorithms

This specification uses the terminology of 'digital signature' for
qualifying indifferently digital signature and message authentication
codes. Thus, the signature algorithms contemplated herein include
public key digital signature algorithms such as ECDSA and message
authentication codes such as HMAC [RFC 2104].

5.2.1 DSA

Public-key signature algorithm proposed by NIST for use with the
Digital Signature Standard. This standard is documented in NIST FIPS
Publication 186 [DSS] and ANSI X9.30 [X9.30].

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The DSA algorithm requires a single parameter, which includes the
canonical digest algorithm to be used for computing the fingerprint
of the signature Manifest.

The DSA URN used in this specification is "urn:nist-gov:dsa".

The DSA uses a canonical or surface-string digest algorithm for
computation of the Manifest fingerprint. The DOM-HASH is recommended
in this specification.

Signature Value Encoding:

The output of this algorithm consists of a pair of integers usually
referred by the pair (r, s). The signature value shall consist of the
concatenation of two octet-streams that respectively result from the
octet-encoding of the values r and s. Integer to octet-stream
conversion shall be done according to PKCS#1 [RFC 2437] specification
with a k parameter equals to 20.

Example
<Algorithm name='urn:nist-gov:dsa' type='signature' ID='P.3'>
<Parameter type='AlgorithmRef'>P.4</Parameter>
</Algorithm>
<Algorithm name='urn:ibm-com:dom-hash' type='digest' ID='P.4'>
<Parameter type='AlgorithmRef'>P.5</Parameter>
</Algorithm>
<Algorithm name='urn:nist-gov:sha1' type='digest' ID='P.5'>
</Algorithm>

5.2.2 HMAC

Message Authentication Code proposed by H. Krawczyk et al., and
documented in [RFC 2104].

This specification adopts a scheme that differs a bit from the common
usage of this algorithm -- computation of the MAC is performed on the
hash of the contents being authenticated instead of the actual
contents. Thence, the actual signature value output by the algorithm
might be depicted as follows:

SignatureValue = HMAC( SecretKey, H(Manifest))

This specification also considered HMAC output truncation such as
proposed by Preneel and van Oorschot. In their paper [PV] these two
researchers have shown some analytical advantages of truncating the
output of hash-based MAC functions. Such output truncation is also
considered in the RFC document.

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HMAC requires three parameters. The first one consists of a canonical
digest algorithm. The second one consists of a hash function. The
last one is optional and specifies the length in bit of the truncated
output. If this last parameter is absent, no truncation shall occur.

The HMAC URN used in this specification is "urn:ietf-org:hmac".

Canonical digest algorithm: Canonical or surface-string digest
algorithm is to be used for computation of the Manifest fingerprint.
The type of this parameter is set to "AlgorithmRef". The recommended
value of this Parameter should be the ID reference for the Algorithm
element DOM-HASH.

Hash-function: Hash function is to be used to compute the MAC value
from the secret key and the fingerprint of the signature Manifest.
The type of this parameter is set to "HashAlgorithmRef" and the value
of this parameter should be set to the ID reference for the Algorithm
element of SHA1.

Output-length: Length in bits of the truncated MAC value. The type of
this parameter is set to "KeyLength" and the value of this parameter
is set the length in bits of the truncated MAC value.

Signature Value Encoding:

The output of this algorithm can be assumed as a large integer value.
The signature value shall consist of the octet-encoded value of this
integer. Integer to octet-stream conversion shall be done according
to PKCS#1 [RFC 2437] specification with a k parameter equals to
((Hlen +7) mod8), Mlen being the length in bits of the MAC value.

Example
<Algorithm name='urn:ietf-org:hmac' type='signature' ID='P.3'>
<Parameter type='AlgorithmRef'>P.4</Parameter>
<Parameter type='HashAlgorithmRef'>P.5</Parameter>
<Parameter type='KeyLength'>128</Parameter>
</Algorithm>
<Algorithm name='urn:ibm-com:dom-hash' type='digest' ID='P.4'>
<Parameter type='AlgorithmRef'>P.5</Parameter>
</Algorithm>
<Algorithm name='urn:nist-gov:sha1' type='digest' ID='P.5'>
</Algorithm>

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5.2.3 RSA

Public-key signature algorithm proposed by RSA Laboratories and
documented in PKCS#1 [RFC 2437].

This specification adopts the RSA encryption algorithm with padding
block type 01. For computing the signature value, the signer shall
first digest the signature Manifest and then encrypt the resulting
digest with his private key.

This signature algorithm requires a single parameter, which consists
of the canonical digest algorithm to be used for computing the
fingerprint of the signature Manifest.

Specifications

The RSA URN used in this specification is "urn:rsasdi-com:rsa-
encription".

The RSA uses a canonical or surface-string digest algorithm for
computation of the Manifest fingerprint. The DOM-HASH is recommended
in this specification.

Signature Value Encoding:

The output of this algorithm consists of single octet-stream. No
further encoding is required.

Example
<Algorithm name='urn:rsasdi-com:rsa-encription'
type='signature' ID='P.3'>
<Parameter type='AlgorithmRef'>P.4</Parameter>
</Algorithm>
<Algorithm name='urn:ibm-com:dom-hash' type='digest' ID='P.4'>
<Parameter type='AlgorithmRef'>P.5</Parameter>
</Algorithm>
<Algorithm name='urn:nist-gov:sha1' type='digest' ID='P.5'>
</Algorithm>

5.2.4 ECDSA

Public-key signature algorithm proposed independently by Neil Koblitz
and Victor Miller. This algorithm is being proposed as an ANSI
standard and is documented in ANSI X9.62 standard proposal [X9.62]
and IEEE/P1363 standard draft proposal [IEEE P1363].

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The ECDSA algorithm requires a single parameter, which consists of
the canonical digest algorithm to be used for computing the
fingerprint of the signature Manifest.

Specifications

The ECDSA URN used in this specification is "urn:ansi-org:ecdsa".

The ECDSA uses a canonical or surface-string digest algorithm for
computation of the Manifest fingerprint. The DOM-HASH [RFC 2803] is
recommended in this specification.

Signature Value Encoding:

The output of this algorithm consists of a pair of integers usually
referred by the pair (r, s). The signature value shall consist of the
concatenation of two octet-streams that respectively result from the
octet-encoding of the values r and s. Integer to octet-stream
conversion shall be done according to PKCS#1 [RFC 2437] specification
with a k parameter equals to 20.

Example
<Algorithm name='urn:ansi-org:ecdsa' type='signature' ID='P.3'>
<Parameter type='AlgorithmRef'>P.4</Parameter>
</Algorithm>
<Algorithm name='urn:ibm-com:dom-hash' type='digest' ID='P.4'>
<Parameter type='AlgorithmRef'>P.5</Parameter>
</Algorithm>
<Algorithm name='urn:nist-gov:sha1' type='digest' ID='P.5'>
</Algorithm>

6. Examples

The following is an example signed IOTP message:

<IotpMessage>
<TransRefBlk ID='M.1'>
<TransId
ID='M.2'
version='1.0'
IotpTransID='[email protected]'
IotpTransType='BaselinePurchase'
TransTimeStamp='1999-08-09T12:58:40.000Z+9'>
</TransId>
<MsgId xml:lang='en' SoftwareID='Iotp wallet version 1.0'>
</MsgId>
</TransRefBlk>
<IotpSignatures>

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<Signature>
<Manifest>
<Algorithm name='urn:nist-gov:sha1'
type='digest' ID='P.3'>
</Algorithm>
<Algorithm name='urn:nist-gov:dsa'
type='signature' ID='P.4'>
<Parameter type='AlgorithmRef'>P.5</Parameter>
</Algorithm>
<Algorithm name='urn:ibm-com:dom-hash'
type='digest' ID='P.5'>
<Parameter type='AlgorithmRef'>P.3</Parameter>
</Algorithm>
<Digest DigestAlgorithmRef='P.6'>
<Locator href='P.1'/>
<Value>
xsqsfasDys2h44u4ehJDe54he5j4dJYTJ
</Value>
</Digest>
<OriginatorInfo
<IssuerAndSerialNumber
issuer='o=Iotp Ltd., c=US'
number='12345678987654'/>
</OriginatorInfo>
<RecipientInfo
SignatureAlgorithmRef='P.4'
</RecipientInfo>
</Manifest>
<Value>
9dj28fjakA9sked0Ks01k2d7a0kgmf9dk19lf63kkDSs0
</Value>
</Signature>
<Certificate type='urn:X500:X509v3'>
<IssuerAndSerialNumber
issuer='o=GlobeSet Inc., c=US'
number='123456789102356'/>
<Value>
xsqsfasDys2h44u4ehJDe54he5j4dJYTJ=
</Value>
</Certificate>
</IotpSignatures>
<PayExchBlk ID='P.1'>
<PaySchemeData
ID='P.2'
PaymentRef='M.5'
ContentSoftwareId='abcdefg'>
<PackagedContent Name='FirstPiece'>
snroasdfnas934k

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</PackagedContent>
</PaySchemeData>
</PayExchBlk>
</IotpMessage>

7. Signature DTD



<!ELEMENT IotpSignatures (Signature+ ,Certificate*) >
<!ATTLIST IotpSignatures
ID ID #IMPLIED
>



<!ELEMENT Signature (Manifest, Value+) >
<!ATTLIST Signature
ID ID #IMPLIED
>

<!ELEMENT Manifest
( Algorithm+,
Digest+,
Attribute*,
OriginatorInfo,
RecipientInfo+
)
>

<!ATTLIST Manifest
LocatorHRefBase CDATA #IMPLIED
>

<!ELEMENT Algorithm (Parameter*) >
<!ATTLIST Algorithm
ID ID #REQUIRED
type (digest|signature) #IMPLIED
name NMTOKEN #REQUIRED
>

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<!ELEMENT Digest (Locator, Value) >
<!ATTLIST Digest
DigestAlgorithmRef IDREF #REQUIRED
>

<!ELEMENT Attribute ANY >
<!ATTLIST Attribute
type NMTOKEN #REQUIRED
critical ( true | false ) #REQUIRED
>

<!ELEMENT OriginatorInfo ANY >
<!ATTLIST OriginatorInfo
OriginatorRef NMTOKEN #IMPLIED
>

<!ELEMENT RecipientInfo ANY >
<!ATTLIST RecipientInfo
SignatureAlgorithmRef IDREF #REQUIRED
SignatureValueRef IDREF #IMPLIED
SignatureCertRef IDREF #IMPLIED
RecipientRefs NMTOKENS #IMPLIED
>

<!ELEMENT KeyIdentifier EMPTY>
<!ATTLIST KeyIdentifier
value CDATA #REQUIRED
>

<!ELEMENT Parameter ANY >
<!ATTLIST Parameter
type CDATA #REQUIRED
>



<!ELEMENT Certificate
( IssuerAndSerialNumber, ( Value | Locator ) )
>

<!ATTLIST Certificate
ID ID #IMPLIED
type NMTOKEN #REQUIRED
>

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RFC 2802 Digital Signatures for IOTP April 2000

<!ELEMENT IssuerAndSerialNumber EMPTY >
<!ATTLIST IssuerAndSerialNumber
issuer CDATA #REQUIRED
number CDATA #REQUIRED
>


<!ELEMENT Value ( #PCDATA ) >
<!ATTLIST Value
ID ID #IMPLIED
encoding (base64|none 'base64'
>

<!ELEMENT Locator EMPTY>
<!ATTLIST Locator
xml:link CDATA #FIXED 'simple'
href CDATA #REQUIRED
>

8. Security Considerations

This entire document concerns the IOTP v1 protocol signature element
which is used for authentication. See the Security Considerations
section of [RFC 2801] "Internet Open Trading Protocol - IOTP, Version
1.0".

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RFC 2802 Digital Signatures for IOTP April 2000

References

[DSA] Federal Information Processing Standards Publication
FIPS PUB 186, "Digital Signature Standard(DSS)", 1994,
<http://csrc.nist.gov>

[IEEE P1363] IEEE P1363, "Standard Specifications for Public-Key
Cryptography", Work in Progress, 1997,
<http://stdsbbs.ieee.org/>

[PV] Preneel, B. and P. van Oorschot, "Building fast MACs
from hash functions", Advances in Cryptology --
CRYPTO'95 Proceedings, Lecture Notes in Computer
Science, Springer-Verlag Vol.963, 1995, pp. 1-14.

[RFC 1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC
1321, April 1992.

[RFC 2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.

[RFC 2046] Freed N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996.

[RFC 2104] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, February
1997.

[RFC 2141] Moats, R., "URN Syntax", RFC 2141, May 1997.

[RFC 2253] Wahl, W., Kille, S. and T. Howes, "Lightweight Directory
Access Protocol (v3): UTF-8 String Representation of
Distinguished Names", RFC 2253, December 1997.

[RFC 2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.

[RFC 2437] Kaliski, B. and J. Staddon, "PKCS #1: RSA Cryptography
Specifications, Version 2.0", RFC 2437, October 1998.

[RFC 2801] Burdett, D., "Internet Open Trading Protocol - IOTP,
Version 1.0", RFC 2801, April 2000.

[RFC 2803] Maruyama, H., Tamura, K. and N. Uramot, "Digest Values
for DOM (DOMHASH)", RFC 2803, April 2000.

Davidson & Kawatsura Informational [Page 26]

RFC 2802 Digital Signatures for IOTP April 2000

[Schneier] Bruce Schneier, "Applied Cryptography: Protocols,
Algorithms, and Source Code in C", 1996, John Wiley and
Sons

[SHA1] NIST FIPS PUB 180-1, "Secure Hash Standard," National
Institute of Standards and Technology, U.S. Department
of Commerce, April 1995.

[X.509] ITU-T Recommendation X.509 (1997 E), "Information
Technology - Open Systems Interconnection - The
Directory: Authentication Framework", June 1997.

[X9.30] ASC X9 Secretariat: American Bankers Association,
"American National Standard for Financial Services -
Public Key Cryptography Using Irreversible Algorithms
for the Financial Services Industry - Part 1: The
Digital Signature Algorithm(DSA)", 1995.

[X9.62] ASC X9 Secretariat: American Bankers
Association,"American National Standard for Financial
Services - Public Key Cryptography Using Irreversible
Algorithms for the Financial Services Industry - The
Elliptic Curve Digital Signature Algorithm (ECDSA)",
Work in Progress, 1997.

[XLink] Eve Maler, Steve DeRose, "XML Linking Language (XLink)",
<http://www.w3.org/TR/1998/WD-xlink-19980303>

[XML] Tim Bray, Jean Paoli, C. M. Sperber-McQueen, "Extensible
Markup Language (XML) 1.0",
<http://www.w3.org/TR/1998/REC-xml-19980210>

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Authors' Addresses

The authors of this document are:

Kent M. Davidson
Differential, Inc.
440 Clyde Ave.
Mountain View, CA 94043 USA

EMail: [email protected]

Yoshiaki Kawatsura
Hitachi, Ltd.
890-12 Kashimada Saiwai Kawasaki,
Kanagawa 2128567 Japan

EMail: [email protected]

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RFC 2802 Digital Signatures for IOTP April 2000

Full Copyright Statement

Copyright (C) The Internet Society (2000). All Rights Reserved.

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.

The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society.

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