Long-term Archive And Notary T. Kunz
Services (LTANS) S. Okunick
Internet-Draft Fraunhofer Institute for Secure
Intended status: Standards Track Information Technology
Expires: April 17, 2008 U. Pordesch
Fraunhofer Gesellschaft
October 15, 2007
Data Structure for Security Suitabilities of Cryptographic Algorithms
(DSSC)
draft-ietf-ltans-dssc-01.txt
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Abstract
In many application areas it must be possible to prove the existence
and integrity of digital signed data. This proof depends on the
security suitability of the used cryptographic algorithms. Because
algorithms can become weak over the years, it is necessary to
periodically evaluate these security suitabilities. When signing or
verifying data, these evaluations must be considered. This document
specifies a data structure for security suitabilities of
cryptographic algorithms which may be automatically interpreted.
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Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Requirements and Assumptions . . . . . . . . . . . . . . . . . 7
3.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 7
4. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. SecuritySuitabilityPolicy . . . . . . . . . . . . . . . . 9
4.2. PolicyName . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3. Publisher . . . . . . . . . . . . . . . . . . . . . . . . 10
4.4. Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.5. PolicyIssueDate . . . . . . . . . . . . . . . . . . . . . 11
4.6. NextUpdate . . . . . . . . . . . . . . . . . . . . . . . . 11
4.7. Algorithm . . . . . . . . . . . . . . . . . . . . . . . . 11
4.8. AlgorithmIdentifier . . . . . . . . . . . . . . . . . . . 12
4.9. Parameter . . . . . . . . . . . . . . . . . . . . . . . . 12
4.10. Validity . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.11. Information . . . . . . . . . . . . . . . . . . . . . . . 14
4.12. Signature . . . . . . . . . . . . . . . . . . . . . . . . 14
5. Definition of Parameters . . . . . . . . . . . . . . . . . . . 15
6. Proceeding . . . . . . . . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1. Normative References . . . . . . . . . . . . . . . . . . . 19
8.2. Informative References . . . . . . . . . . . . . . . . . . 19
Appendix A. Example of a Policy . . . . . . . . . . . . . . . . . 21
Appendix B. Verification of Evidence Records using DSSC . . . . . 25
Appendix C. XML schema . . . . . . . . . . . . . . . . . . . . . 26
Appendix D. ASN.1 Module in 1988 Syntax . . . . . . . . . . . . . 29
Appendix E. ASN.1 Module in 1997 Syntax . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
Intellectual Property and Copyright Statements . . . . . . . . . . 36
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1. Introduction
1.1. Motivation
Digital signatures are means to provide data integrity and
authentication. They are based on cryptographic algorithms, which
must have certain security properties. For example, hash algorithms
have to be resistant to collisions and in case of public key
algorithms it must not be possible to compute the private key of a
given public key. If algorithms did not have the required
properties, signatures could be forged.
Very few algorithms satisfy the security requirements and are
suitable for usage in signatures. Besides, because of the increasing
performance of computers and progresses in cryptography, algorithms
or their parameters become insecure over the years. E.g. the hash
algorithm MD5 is impractical by now. A digital signature using such
"weak" algorithms may lose its probative value. Every kind of
digital signed data like signed documents, time stamps, certificates,
and revocation lists is affected, in particular in the case of long-
term archiving. Over long periods of time, it is realistic to assume
that the algorithms used in signatures become insecure.
For this reason, it is important to periodically reevaluate
algorithms regarding their security properties and to consider these
evaluations when creating, verifying or renewing signatures. Such
evaluations will give a prognosis how long an algorithm will be
presumably secure and help to detect, whether insecure algorithms are
used in a signature or whether signatures have been timely renewed.
The evaluation of security suitabilites of algorithms cannot be done
by the user itself. They are made by expert committees after long
scientific discussion and published by specific evaluation
institutions. In Germany the Federal Network Agency annually
publishes a current evaluation of cryptografic algorithms
[BNetzAg.2007]. Examples for European and international evaluations
are [NIST.800-57-Part1.2006] and [ETSI-TS102176-1-2005].
These publications evaluate algorithms in a textual form and are not
interpretable by computer programs. Therefore it is necessary to
define an automatically interpretable data structure holding the
algorithm evaluations. In this way evaluation institutions are able
use the standardized form for publication. Such policies can be
interpreted by e.g. signing and verification tools. In the
following, such evaluations are called security suitability policy.
This document specifies a data structure for security suitability
policies.
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1.2. Use Cases
In the following we present some use cases for security suitability
policies.
Long-term archiving: The most important use case for security
suitability policies is the long-term archiving of signed data.
Algorithms or their parameters become insecure over very long
periods of time. Therefore signatures of archived data and
timestamps have to be periodically renewed. Policies provide
informations about suitable and threatened algorithms.
Additionally the policies assist in verifying archived and re-
signed documents.
Services: Services may provide information about cryptographic
algorithms. E.g. such services can use these policies to provide
the date when an algorithm became insecure or presumably will
become insecure or to provide all algorithms which are presently
valid. Such services could be used by verification tools or long-
term archiving systems so that they do not need to deal with the
algorithm security by themselves.
Long-term Archive Services (LTA) as defined in [RFC4810]) may use
the policies for signature renewal. Additionally the policies may
be integrated in Evidence Records (ERS, [RFC4998]) as further
validation data.
Signing and verifying: When signing documents, certificates or
attestations, e.g. within an LTAP transaction
([I-D.ietf-ltans-ltap]), it has to be assured that the algorithms
which will be used for signing are suitable. Accordingly when
verifying e.g CMS ([RFC3852]) or XML signatures ([RFC3275],
[ETSI-TS101903]), not only the validity of the certificates may be
checked, but also the validity of the used algorithms.
Reencryption: Security suitability policies can also be used to
decide if encrypted documents must be reencrypted because the
encryption algorithm is no longer secure.
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2. Terminology
Algorithm: In the context of this document, a cryptographic
algorithm, i.e. a public key or hash algorithm. For public key
algorithms this is the algorithm with its parameters.
Operator: Instance which uses and interprets a policy, e.g. a
signature component.
Policy: In this document, an abbreviation for security suitability
policy.
Publisher: Instance that publishes the evaluation of algorithms in
form of policies.
Security suitability policy: The evaluation of cryptographic
algorithms according to their security in a specific application
area, e.g. signing or verifying data. The evaluation is published
in an electronic format.
Suitable algorithm: An algorithm which is evaluated in a policy,
i.e. is rated to be valid.
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3. Requirements and Assumptions
This section first describes general requirements for a data
structure containing the securitiy suitabilities of algorithms.
Afterwards model assumptions are specified concerning both the design
and the usage of the data structure.
An evaluation of the security suitability of algorithms results in a
policy. It contains a list of the evaluated algorithms. An
evaluated algorithm is described by its identifier, security
constraints and predicted validity period. By these constraints the
requirements for algorithm properties must be defined, e.g. a public
key algorithm is evaluated on the basis of its parameter.
3.1. Requirements
Automatic interpretation: The data structure of the policy must
allow an automatic interpretation in order to consider the
security suitabilities of algorithms when signing, verifying or
renewing signatures.
Flexibility: The data structure must be flexible enough to support
new algorithms. In a future policy publication an algorithm could
be included, that is currently unknown. It must be possible to
add new algorithms with the corresponding security constraints in
the data structure. Besides, the data structure must be
independent of the intended purpose, e.g. signing, verifying, and
signature renewing.
Considering different policies: Policies may be published by
different institutions, e.g. on national or EU level, whereas one
policy needs not to be in agreement with the other one.
Furthermore organizations may undertake own evaluations for
internal purposes. For this reason a policy must be attributable
to its publisher.
Integrity and authenticity: The integrity and authenticity of a
published security suitability policy should be assured. The
publisher must be able to sign the policy so that operators may
prove the identity and trustworthiness of a policy.
3.2. Assumptions
We assume that a security suitability policy contains the evaluations
of all currently known algorithms, including the expired ones.
The latest policy is significant to decide whether an algorithm is
currently suitable. An algorithm is valid now if it is contained in
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the current policy and the end of the validity period is in the
future, respectivly open-end.
If an algorithm appears in a policy for the first time, it will be
assumed that the algorithm has already been suitable in the past.
Generally an algorithm is used in practice before it is evaluated.
To avoid inconsistencies, multiple instances of the same algorithm
definition as well as validity overlaps for one algorithm are
prohibited. It is up to the publisher to take care about preventing
conflicts within a policy.
Assertions made in the policy are suitable at least until the next
policy is published.
An algorithm once expired must not get valid again in a future
policy. There must not be any gaps in the validity periods.
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4. Data Structures
This section describes the syntax of a security suitability policy
defined as an XML schema. The ASN.1 modules are defined in
Appendix D and Appendix E. The schema uses the following namespace:
http://www.sit.fraunhofer.de/dssc
Within this document, the prefix "dssc" is used for this namespace.
The schema starts with the following schema definition:
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:dssc="http://www.sit.fraunhofer.de/dssc"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
targetNamespace="http://www.sit.fraunhofer.de/dssc"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<xs:import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/xml.xsd"/>
<xs:import namespace="http://www.w3.org/2000/09/xmldsig#"
schemaLocation="xmldsig-core-schema.xsd"/>
4.1. SecuritySuitabilityPolicy
The SecuritySuitabilityPolicy element is the root element of a
policy. It has an optional id attribute which must be used as a
reference when signing the policy (Section 4.12). The element is
defined by the following schema:
<xs:element name="SecuritySuitabilityPolicy"
type="dssc:SecuritySuitabilityPolicyType"/>
<xs:complexType name="SecuritySuitabilityPolicyType">
<xs:sequence>
<xs:element ref="dssc:PolicyName"/>
<xs:element ref="dssc:Publisher"/>
<xs:element name="PolicyIssueDate" type="xs:dateTime"/>
<xs:element name="NextUpdate" type="xs:dateTime" minOccurs="0"/>
<xs:element ref="dssc:Algorithm" maxOccurs="unbounded"/>
<xs:element ref="ds:Signature" minOccurs="0"/>
</xs:sequence>
<xs:attribute name="version" type="xs:string" default="1"/>
<xs:attribute name="id" type="xs:ID"/>
</xs:complexType>
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4.2. PolicyName
The PolicyName element contains the name of the policy. It consists
of an arbitrary name and an optional Uniform Resource Identifier
(URI).
<xs:element name="PolicyName" type="dssc:PolicyNameType"/>
<xs:complexType name="PolicyNameType">
<xs:sequence>
<xs:element ref="dssc:Name"/>
<xs:element ref="dssc:URI" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:element name="Name" type="xs:string"/>
<xs:element name="URI" type="xs:anyURI"/>
4.3. Publisher
The Publisher element contains information about the publisher of the
policy. It is composed of the name, e.g. name of institution, an
optional address, and an optional URI.
<xs:element name="Publisher" type="dssc:PublisherType"/>
<xs:complexType name="PublisherType">
<xs:sequence>
<xs:element ref="dssc:Name"/>
<xs:element ref="dssc:Address" minOccurs="0"/>
<xs:element ref="dssc:URI" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
4.4. Address
The Address element consists of the street, the locality, the
optional state or province, the postal code, and the country.
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<xs:element name="Address" type="dssc:AddressType"/>
<xs:complexType name="AddressType">
<xs:sequence>
<xs:element name="Street" type="xs:string"/>
<xs:element name="Locality" type="xs:string"/>
<xs:element name="StateOrProvince" type="xs:string" minOccurs="0"/>
<xs:element name="PostalCode" type="xs:string"/>
<xs:element name="Country" type="xs:string"/>
</xs:sequence>
</xs:complexType>
4.5. PolicyIssueDate
The PolicyIssueDate element indicates the point of time when the
policy was issued.
4.6. NextUpdate
The optional NextUpdate element may be used to indicate when the next
policy will be issued.
4.7. Algorithm
A security suitability policy must contain at least one Algorithm
element. An Algorithm element describes the evaluation of one
cryptographic algorithm. An algorithm is identified by an
AlgorithmIdentifier element. Additionally specific parameter
constraints, e.g. a modulus length, may be specified. The
suitability of the algorithm is expressed by a validity period. The
Algorithm element is defined by the following schema:
<xs:element name="Algorithm" type="dssc:AlgorithmType"/>
<xs:complexType name="AlgorithmType">
<xs:sequence>
<xs:element ref="dssc:AlgorithmIdentifier"/>
<xs:element ref="dssc:Parameter" minOccurs="0"
maxOccurs="unbounded"/>
<xs:element ref="dssc:Validity"/>
<xs:element ref="dssc:Information" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
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4.8. AlgorithmIdentifier
The AlgorithmIdentifier element is used to identify a cryptographic
algorithm. It consists of the algorithm name and optionally one or
more object identifers and URIs. The element is defined as follows:
<xs:element name="AlgorithmIdentifier"
type="dssc:AlgorithmIdentifierType"/>
<xs:complexType name="AlgorithmIdentifierType">
<xs:sequence>
<xs:element ref="dssc:Name"/>
<xs:element name="ObjectIdentifier" type="xs:string"
minOccurs="0" maxOccurs="unbounded"/>
<xs:element ref="dssc:URI" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
4.9. Parameter
By the Parameter element, constraints on algorithm specific
parameters are expressed. E.g. the suitability of the RSA algorithm
depends on the "modulus" parameter (RSA with a modulus length of 1024
may have another suitability period as RSA with a modulus length of
2048). Note that not all algorithm suitabilities depend on parameter
constraints, e.g. current hash algorithms like SHA-1 or RIPEMD-160 do
not have any parameters.
The Parameter element has a name attribute which holds the name of
the parameter (e.g. "modulus" for RSA [RFC2437]). Besides a better
readability of the policy, the attribute may be used by
implementations for output messages. In Section 5 the parameter
names of currently known signature algorithms are defined. For the
actual parameter, an exact value or a range of values can be defined.
These constraints are expressed by the following elements:
Exact: The Exact element specifies the exact value of the parameter.
Min: The Min element defines the minimum value of the parameter.
That means, also all other values greater than the given one meet
the requirements.
Max: The Max element defines the maximum value the parameter may
take.
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Range: The Range element is used to define a range of values,
consisting of a minimum and a maximum value. The parameter may
have any value within the defined range.
For one algorithm it is recommended not to mix these elements in
order to avoid inconsistencies.
These constraints are sufficient for all current algorithms. If
future algorithms will need constraints which cannot be expressed by
the elements above, an arbitrary XML structure may be inserted which
meets the new constraints. For this reason, the Parameter element
contains an "any" element. The schema for the Parameter element is
as follows:
<xs:element name="Parameter" type="dssc:ParameterType"/>
<xs:complexType name="ParameterType">
<xs:choice>
<xs:element name="Exact" type="xs:string"/>
<xs:element ref="dssc:Min"/>
<xs:element ref="dssc:Max"/>
<xs:element name="Range">
<xs:complexType>
<xs:sequence>
<xs:element ref="dssc:Min"/>
<xs:element ref="dssc:Max"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:any namespace="##other"/>
</xs:choice>
<xs:attribute name="name" type="xs:string" use="required"/>
</xs:complexType>
<xs:element name="Min" type="xs:string"/>
<xs:element name="Max" type="xs:string"/>
4.10. Validity
The Validity element is used to define the period of the (predicted)
suitability of the algorithm. It is composed of an optional start
date and an optional end date. Defining no end date means the
algorithm has an open-end validity. Of course this may be restricted
by a future policy which sets an end date for the algorithm. If the
end of the validity period is in the past, the algorithm is not
suitable. The element is defined by the following schema:
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<xs:element name="Validity" type="dssc:ValidityType"/>
<xs:complexType name="ValidityType">
<xs:sequence>
<xs:element name="Start" type="xs:date" minOccurs="0"/>
<xs:element name="End" type="xs:date" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
4.11. Information
The Information element may be used to give additional textual
information about the algorithm or the evaluation, e.g. references on
algorithm specifications. The element is defined as follows:
<xs:element name="Information" type="dssc:InformationType"/>
<xs:complexType name="InformationType">
<xs:sequence>
<xs:element name="Text" maxOccurs="unbounded">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="lang"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
4.12. Signature
The optional Signature element may be used to guarantee the integrity
and authenticity of the policy. It is an XML signature specified in
[RFC3275]. The signature must relate to the
SecuritySuitabilityPolicy element. If the Signature element is set,
the SecuritySuitabilityPolicy element must have the optional id
attribute. This attribute must be used to reference the
SecuritySuitabilityPolicy element within the Signature element.
Since it is an enveloped signature, the signature must use the
transformation algorithm identified by the following URI:
http://www.w3.org/2000/09/xmldsig#enveloped-signature
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5. Definition of Parameters
This section defines the parameter names for the currently known
public key algorithms. The signature algorithms RSA [RFC2437] and
DSA [FIPS.186-1.1998] are always used in conjunction with a one-way
hash algorithm. RSA with RIPEMD-160 is such a combined algorithm
with its own object identifier. RSA and DSA may be combined with the
suitable hash algorithms SHA-1, SHA-224, SHA-256, SHA-384, SHA-512,
and RIPEMD-160. The following parameters refer to the appropriate
combined algorithms as well.
The parameter of RSA should be named "modulus".
The parameters for DSA should be "p" and "q".
Publisher of policies must use the same parameter names, so that the
correct interpretation is guaranteed.
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6. Proceeding
This section describes how to analyze a policy, i.e. how to extract
the informations out of the policy needed by the different use cases.
To get these informations, the latest policy containing all
algorithms is relevant.
1. Is an algorithm currently valid?
Procedure: The wanted algorithm has to be listed in the current
policy. The algorithm is valid, if its validity end date is in
the future or not defined.
Input: algorithm
Response: true or false
2. Did an algorithm have been valid at a particular date in the
past?
Procedure: The algorithm is valid, if it is listed in the current
policy and the end of the validity period is after the particular
date or is not defined.
Input: algorithm and date
Response: true or false
3. Until which date in the future an algorithm is predicted to be
valid?
Procedure: The wanted algorithm has to be listed in the current
policy. If the end date of the algorithm is in the future, this
is the predicted date. If the validity end date is not defined,
the algorithm is valid open-end.
Input: algorithm
Response: date or null (open-end) or error, if the algorithm does
not exist or the validity end date is in the past
4. At which date an algorithm became invalid?
Procedure: The wanted algorithm has to be listed in the current
policy. The particular date is the validity end date of the
listed algorithm, which has to be in the past.
Input: algorithm
Response: date or error, if date has never been valid or is valid
now
5. Which algorithms are currently valid?
Procedure: All algorithms included in the current policy are
valid whose validity end date is in the future or is not defined.
Response: list of algorithms
6. Which algorithms have been valid at a particular date in the
past?
Procedure: All algorithms included in the current policy are
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valid whose validity end date is after the particular date or is
not defined. Additionally any algorithm newly added in one
following policy has been valid.
Input: date
Response: list of algorithms
To determine the validity of a particular algorithm, first the
algorithm definition has to be found in the policy. Therefore, the
algorithm identifier has to match and the parameter constraints have
to be fulfilled. To fulfill means, the exact value is given or a
parameter fulfills the constraint definition if its value matches the
exactly defined value or is in the defined range.
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7. Security Considerations
The used policies for security suitabilities have great impact on the
quality of signatures and verification results. If evaluations of
algorithms are wrong, signatures with a low probative force could be
created and verification results could be incorrect. The following
security considerations have been identified:
1. An institution publishing a policy must take care via
organizational measures that unauthorized manipulation of
security suitabilities is impossible before a policy is signed
and published.
2. A client should only accept signed policies issued by a trusted
institution. It must not be possible to unnoticeably manipulate
or replace security suitabilities once accepted by the client.
3. A threat arises when a client downloads a policy too late
although the policy has already been published. In this case,
the client would work with obsolete security suitabilities. To
minimize this risk, the client should periodically check if new
policies are published. This check could be done automatically
by signature and verification components.
4. When signing a policy, only algorithms should be used which are
suitable according this policy.
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8. References
8.1. Normative References
[ETSI-TS101903]
European Telecommunication Standards Institute (ETSI),
"XML Advanced Electronic Signatures (XAdES)", ETSI TS 101
903, Feb 2002.
[I-D.ietf-ltans-ltap]
Jerman-Blazic, A., "Long-term Archive Protocol (LTAP)",
draft-ietf-ltans-ltap-05 (work in progress), July 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3275] Eastlake, D., Reagle, J., and D. Solo, "(Extensible Markup
Language) XML-Signature Syntax and Processing", RFC 3275,
March 2002.
[RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.
[RFC3852] Housley, R., "Cryptographic Message Syntax (CMS)",
RFC 3852, July 2004.
[RFC4810] Wallace, C., Pordesch, U., and R. Brandner, "Long-Term
Archive Service Requirements", RFC 4810, March 2007.
[RFC4998] Gondrom, T., Brandner, R., and U. Pordesch, "Evidence
Record Syntax (ERS)", RFC 4998, August 2007.
8.2. Informative References
[BNetzAg.2007]
Federal Network Agency for Electricity, Gas,
Telecommunications, Post and Railway, "Bekanntmachung zur
elektronischen Signatur nach dem Signaturgesetz und der
Signaturverordnung (Uebersicht ueber geeignete
Algorithmen)", April 2007,
<http://www.bundesnetzagentur.de/media/archive/9655.pdf>.
[ETSI-TS102176-1-2005]
European Telecommunication Standards Institute (ETSI),
"Electronic Signatures and Infrastructures (ESI);
"Algorithms and Parameters for Secure Electronic
Kunz, et al. Expires April 17, 2008 [Page 19]
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Signatures; Part 1: Hash functions and asymmetric
algorithms"", ETSI TS 102 176-1 V1.2.1, July 2005.
[FIPS.186-1.1998]
National Institute of Standards and Technology, "Digital
Signature Standard", FIPS PUB 186-1, December 1998,
<http://csrc.nist.gov/fips/fips1861.pdf>.
[NIST.800-57-Part1.2006]
National Institute of Standards and Technology,
"Recommendation for Key Management - Part 1: General
(Revised)", NIST 800-57 Part1, May 2006.
[RFC2437] Kaliski, B. and J. Staddon, "PKCS #1: RSA Cryptography
Specifications Version 2.0", RFC 2437, October 1998.
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Appendix A. Example of a Policy
In the following an example of a policy is presented. It is
generated on the basis of the last evaluation of the German Federal
Network Agency ([BNetzAg.2007]). The policy consists on hash
algorithms as well as public key algorithms. RSA with modulus length
of 768 is an example for an expired algorithm.
<SecuritySuitabilityPolicy xmlns="http://www.sit.fraunhofer.de/dssc"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<PolicyName>
<Name>Evaluation of suitable signature algorithms 2007</Name>
</PolicyName>
<Publisher>
<Name>Federal Network Agency</Name>
</Publisher>
<PolicyIssueDate>2007-04-12T00:00:00</PolicyIssueDate>
<Algorithm>
<AlgorithmIdentifier>
<Name>RIPEMD-160</Name>
<ObjectIdentifier>1.3.36.3.2.1</ObjectIdentifier>
</AlgorithmIdentifier>
<Validity><End>2010-12-31</End></Validity>
</Algorithm>
<Algorithm>
<AlgorithmIdentifier>
<Name>SHA-256</Name>
<ObjectIdentifier>2.16.840.1.101.3.4.2.1</ObjectIdentifier>
</AlgorithmIdentifier>
<Validity><End>2012-12-31</End></Validity>
</Algorithm>
<Algorithm>
<AlgorithmIdentifier>
<Name>SHA-384</Name>
<ObjectIdentifier>2.16.840.1.101.3.4.2.2</ObjectIdentifier>
</AlgorithmIdentifier>
<Validity><End>2012-12-31</End></Validity>
</Algorithm>
<Algorithm>
<AlgorithmIdentifier>
<Name>SHA-512</Name>
<ObjectIdentifier>2.16.840.1.101.3.4.2.3</ObjectIdentifier>
</AlgorithmIdentifier>
<Validity><End>2012-12-31</End></Validity>
</Algorithm>
<Algorithm>
<AlgorithmIdentifier>
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<Name>SHA-224</Name>
<ObjectIdentifier>2.16.840.1.101.3.4.2.4</ObjectIdentifier>
</AlgorithmIdentifier>
<Validity><End>2012-12-31</End></Validity>
</Algorithm>
<Algorithm>
<AlgorithmIdentifier>
<Name>SHA-1</Name>
<ObjectIdentifier>1.3.14.3.2.26</ObjectIdentifier>
</AlgorithmIdentifier>
<Validity><End>2009-12-31</End></Validity>
</Algorithm>
<Algorithm>
<AlgorithmIdentifier>
<Name>RSA 768</Name>
<ObjectIdentifier>1.3.14.3.2.26</ObjectIdentifier>
</AlgorithmIdentifier>
<Parameter name="modulus"><Min>768</Min></Parameter>
<Validity><End>2000-12-31</End></Validity>
</Algorithm>
<Algorithm>
<AlgorithmIdentifier>
<Name>RSA 1024</Name>
<ObjectIdentifier>1.3.14.3.2.26</ObjectIdentifier>
</AlgorithmIdentifier>
<Parameter name="modulus"><Min>1024</Min></Parameter>
<Validity><End>2007-12-31</End></Validity>
</Algorithm>
<Algorithm>
<AlgorithmIdentifier>
<Name>RSA 1280</Name>
<ObjectIdentifier>1.3.14.3.2.26</ObjectIdentifier>
</AlgorithmIdentifier>
<Parameter name="modulus"><Min>1280</Min></Parameter>
<Validity><End>2008-12-31</End></Validity>
</Algorithm>
<Algorithm>
<AlgorithmIdentifier>
<Name>RSA 1536</Name>
<ObjectIdentifier>1.3.14.3.2.26</ObjectIdentifier>
</AlgorithmIdentifier>
<Parameter name="modulus"><Min>1536</Min></Parameter>
<Validity><End>2009-12-31</End></Validity>
</Algorithm>
<Algorithm>
<AlgorithmIdentifier>
<Name>RSA 1728</Name>
<ObjectIdentifier>1.3.14.3.2.26</ObjectIdentifier>
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</AlgorithmIdentifier>
<Parameter name="modulus"><Min>1728</Min></Parameter>
<Validity><End>2010-12-31</End></Validity>
</Algorithm>
<Algorithm>
<AlgorithmIdentifier>
<Name>RSA 1976</Name>
<ObjectIdentifier>1.2.840.113549.1.1.1</ObjectIdentifier>
</AlgorithmIdentifier>
<Parameter name="modulus"><Min>1976</Min></Parameter>
<Validity><End>2012-12-31</End></Validity>
</Algorithm>
<Algorithm>
<AlgorithmIdentifier>
<Name>DSA 1024</Name>
<ObjectIdentifier>1.2.840.10040.4.1</ObjectIdentifier>
<ObjectIdentifier>1.3.14.3.2.12</ObjectIdentifier>
</AlgorithmIdentifier>
<Parameter name="p"><Min>1024</Min></Parameter>
<Parameter name="q"><Min>160</Min></Parameter>
<Validity><End>2007-12-31</End></Validity>
</Algorithm>
<Algorithm>
<AlgorithmIdentifier>
<Name>DSA 1280</Name>
<ObjectIdentifier>1.2.840.10040.4.1</ObjectIdentifier>
<ObjectIdentifier>1.3.14.3.2.12</ObjectIdentifier>
</AlgorithmIdentifier>
<Parameter name="p"><Min>1280</Min></Parameter>
<Parameter name="q"><Min>160</Min></Parameter>
<Validity><End>2008-12-31</End></Validity>
</Algorithm>
<Algorithm>
<AlgorithmIdentifier>
<Name>DSA 1536</Name>
<ObjectIdentifier>1.2.840.10040.4.1</ObjectIdentifier>
<ObjectIdentifier>1.3.14.3.2.12</ObjectIdentifier>
</AlgorithmIdentifier>
<Parameter name="p"><Min>1536</Min></Parameter>
<parameter name="q"><Min>160</Min></Parameter>
<Validity><End>2009-12-31</End></Validity>
</Algorithm>
<Algorithm>
<AlgorithmIdentifier>
<Name>DSA 2048</Name>
<ObjectIdentifier>1.2.840.10040.4.1</ObjectIdentifier>
<ObjectIdentifier>1.3.14.3.2.12</ObjectIdentifier>
</AlgorithmIdentifier>
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<Parameter name="p"><Min>2048</Min></Parameter>
<Parameter name="q"><Min>224</Min></Parameter>
<Validity><End>2012-12-31</End></Validity>
</Algorithm>
</SecuritySuitabilityPolicy>
Combined algorithms should also be part of the policy since some
programs know the object identifiers of combined algorithms instead
of the general public key algorithm. The following excerpt describes
a combined algorithm. The validity end date is given by the end
dates of RSA and RIPEMD-160, in particular it is the former one.
Combined algorithms could replace the public key algorithms in the
policy example. They could also be listed together with public key
algorithms.
<Algorithm>
<AlgorithmIdentifier>
<Name>RIPEMD-160 with RSA</Name>
<ObjectIdentifier>1.3.36.3.3.1.2</ObjectIdentifier>
</AlgorithmIdentifier>
<Parameter name="modulus"><Min>1024</Min></Parameter>
<Validity><End>2007-12-31</End></Validity>
</Algorithm>
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Appendix B. Verification of Evidence Records using DSSC
This section describes the verification of an Evidence Record
according to the Evidence Record Syntax [RFC4998] by using the
presented data structure.
An Evidence Record contains a sequence of archiveTimeStampChains
which consist of ArchiveTimeStamps. For each archiveTimeStamp the
hash algorithm used for the hash tree (digestAlgorithm) and the
public key algorithm and hash algorithm in the time stamp signature
have to be examined. The definitive date is the time information in
the time stamp (date of issue). Starting with the first
ArchiveTimestamp it has to be assured that
1. The time stamp uses public key and hash algorithms which have
been suitable at the date of issue.
2. The hashtree was build with an hash algorithm that has been
suitable at the date of issue as well.
3. Algorithms for time stamp and hashtree in the preceding
ArchiveTimestamp must have been suitable at the issuing date of
considered ArchiveTimestamp.
4. Algorithms in the last ArchiveTimstamp have to be suitable now.
If the check of one of these item fails, this will lead to a failure
of the verification.
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Appendix C. XML schema
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:dssc="http://www.sit.fraunhofer.de/dssc"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
targetNamespace="http://www.sit.fraunhofer.de/dssc"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<xs:import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/xml.xsd"/>
<xs:import namespace="http://www.w3.org/2000/09/xmldsig#"
schemaLocation="xmldsig-core-schema.xsd"/>
<xs:element name="SecuritySuitabilityPolicy"
type="dssc:SecuritySuitabilityPolicyType"/>
<xs:complexType name="SecuritySuitabilityPolicyType">
<xs:sequence>
<xs:element ref="dssc:PolicyName"/>
<xs:element ref="dssc:Publisher"/>
<xs:element name="PolicyIssueDate" type="xs:dateTime"/>
<xs:element name="NextUpdate" type="xs:dateTime" minOccurs="0"/>
<xs:element ref="dssc:Algorithm" maxOccurs="unbounded"/>
<xs:element ref="ds:Signature" minOccurs="0"/>
</xs:sequence>
<xs:attribute name="version" type="xs:string" default="1"/>
<xs:attribute name="id" type="xs:ID"/>
</xs:complexType>
<xs:element name="PolicyName" type="dssc:PolicyNameType"/>
<xs:complexType name="PolicyNameType">
<xs:sequence>
<xs:element ref="dssc:Name"/>
<xs:element ref="dssc:URI" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:element name="Publisher" type="dssc:PublisherType"/>
<xs:complexType name="PublisherType">
<xs:sequence>
<xs:element ref="dssc:Name"/>
<xs:element ref="dssc:Address" minOccurs="0"/>
<xs:element ref="dssc:URI" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:element name="Name" type="xs:string"/>
<xs:element name="URI" type="xs:anyURI"/>
<xs:element name="Address" type="dssc:AddressType"/>
<xs:complexType name="AddressType">
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<xs:sequence>
<xs:element name="Street" type="xs:string"/>
<xs:element name="Locality" type="xs:string"/>
<xs:element name="StateOrProvince" type="xs:string"
minOccurs="0"/>
<xs:element name="PostalCode" type="xs:string"/>
<xs:element name="Country" type="xs:string"/>
</xs:sequence>
</xs:complexType>
<xs:element name="Algorithm" type="dssc:AlgorithmType"/>
<xs:complexType name="AlgorithmType">
<xs:sequence>
<xs:element ref="dssc:AlgorithmIdentifier"/>
<xs:element ref="dssc:Parameter" minOccurs="0"
maxOccurs="unbounded"/>
<xs:element ref="dssc:Validity"/>
<xs:element ref="dssc:Information" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:element name="AlgorithmIdentifier"
type="dssc:AlgorithmIdentifierType"/>
<xs:complexType name="AlgorithmIdentifierType">
<xs:sequence>
<xs:element ref="dssc:Name"/>
<xs:element name="ObjectIdentifier" type="xs:string"
minOccurs="0" maxOccurs="unbounded"/>
<xs:element ref="dssc:URI" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:element name="Validity" type="dssc:ValidityType"/>
<xs:complexType name="ValidityType">
<xs:sequence>
<xs:element name="Start" type="xs:date" minOccurs="0"/>
<xs:element name="End" type="xs:date" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:element name="Information" type="dssc:InformationType"/>
<xs:complexType name="InformationType">
<xs:sequence>
<xs:element name="Text" maxOccurs="unbounded">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="lang"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
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</xs:sequence>
</xs:complexType>
<xs:element name="Parameter" type="dssc:ParameterType"/>
<xs:complexType name="ParameterType">
<xs:choice>
<xs:element name="Exact" type="xs:string"/>
<xs:element ref="dssc:Min"/>
<xs:element ref="dssc:Max"/>
<xs:element name="Range">
<xs:complexType>
<xs:sequence>
<xs:element ref="dssc:Min"/>
<xs:element ref="dssc:Max"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:any namespace="##other"/>
</xs:choice>
<xs:attribute name="name" type="xs:string" use="required"/>
</xs:complexType>
<xs:element name="Min" type="xs:string"/>
<xs:element name="Max" type="xs:string"/>
</xs:schema>
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Appendix D. ASN.1 Module in 1988 Syntax
ASN.1-Module
DSSC {...} -- TODO: define OID!
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORT ALL --
IMPORTS
-- Imports from RFC 3280 [RFC3280], Appendix A.1
UTF8String, AlgorithmIdentifier, Certificate
FROM PKIX1Explicit88
{ iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7)
mod(0) pkix1-explicit(18) }
;
SecuritySuitabilityPolicy ::= SEQUENCE {
tbsPolicy TBSPolicy,
signature Signature OPTIONAL
}
TBSPolicy ::= SEQUENCE {
version INTEGER { v1(1) } OPTIONAL,
policyName PolicyName,
publisher Publisher,
policyIssueDate GeneralizedTime,
nextUpdate GeneralizedTime OPTIONAL,
algorithms SEQUENCE OF Algorithm
}
PolicyName ::= SEQUENCE {
name UTF8String,
oid OBJECT IDENTIFIER OPTIONAL
}
Publisher ::= SEQUENCE {
name UTF8String,
address [0] Address OPTIONAL,
uri [1] IA5String OPTIONAL
}
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Address ::= SEQUENCE {
street [0] UTF8String,
locality [1] UTF8String,
stateOrProvince [2] UTF8String OPTIONAL,
postalCode [3] UTF8String,
country [4] UTF8String
}
Algorithm ::= SEQUENCE {
algorithmIdentifier AlgID,
parameters [0] SEQUENCE OF Parameter OPTIONAL,
validity [1] Validity,
information [2] SEQUENCE OF UTF8String OPTIONAL
}
AlgID ::= SEQUENCE {
name UTF8String,
oid [0] SEQUENCE OF OBJECT IDENTIFIER OPTIONAL,
uri [1] SEQUENCE OF IA5String OPTIONAL
}
Parameter ::= SEQUENCE {
name UTF8String,
constraint CHOICE {
exact [0] OCTET STRING,
min [1] OCTET STRING,
max [2] OCTET STRING,
range [3] Range,
other [4] OtherConstraints
}
}
OtherConstraints ::= SEQUENCE {
otherConstraintType OBJECT IDENTIFIER,
otherConstraint ANY DEFINED BY otherConstraintType
}
Range ::= SEQUENCE {
min [0] OCTET STRING,
max [1] OCTET STRING
}
Validity ::= SEQUENCE {
start [0] GeneralizedTime OPTIONAL,
end [1] GeneralizedTime OPTIONAL
}
Signature ::= SEQUENCE {
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signatureAlgorithm AlgorithmIdentifier,
signature OCTET STRING,
certificates SEQUENCE OF Certificate OPTIONAL
}
END
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Appendix E. ASN.1 Module in 1997 Syntax
ASN.1-Module
DSSC {...} -- TODO: define OID!
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORT ALL --
IMPORTS
-- Imports from AuthenticationFramework
AlgorithmIdentifier, Certificate
FROM AuthenticationFramework
{joint-iso-itu-t ds(5) module(1)
authenticationFramework(7) 4}
;
SecuritySuitabilityPolicy ::= SEQUENCE {
tbsPolicy TBSPolicy,
signature Signature OPTIONAL
}
TBSPolicy ::= SEQUENCE {
version INTEGER { v1(1) } OPTIONAL,
policyName PolicyName,
publisher Publisher,
policyIssueDate GeneralizedTime,
nextUpdate GeneralizedTime OPTIONAL,
algorithms SEQUENCE OF Algorithm
}
PolicyName ::= SEQUENCE {
name UTF8String,
oid OBJECT IDENTIFIER OPTIONAL
}
Publisher ::= SEQUENCE {
name UTF8String,
address [0] Address OPTIONAL,
uri [1] IA5String OPTIONAL
}
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Address ::= SEQUENCE {
street [0] UTF8String,
locality [1] UTF8String,
stateOrProvince [2] UTF8String OPTIONAL,
postalCode [3] UTF8String,
country [4] UTF8String
}
Algorithm ::= SEQUENCE {
algorithmIdentifier AlgID,
parameters [0] SEQUENCE OF Parameter OPTIONAL,
validity [1] Validity,
information [2] SEQUENCE OF UTF8String OPTIONAL
}
AlgID ::= SEQUENCE {
name UTF8String,
oid [0] SEQUENCE OF OBJECT IDENTIFIER OPTIONAL,
uri [1] SEQUENCE OF IA5String OPTIONAL
}
Parameter ::= SEQUENCE {
name UTF8String,
constraint CHOICE {
exact [0] OCTET STRING,
min [1] OCTET STRING,
max [2] OCTET STRING,
range [3] Range,
other [4] OtherConstraints
}
}
OtherConstraints ::= SEQUENCE {
otherConstraintType CONSTRAINT-TYPE.&id ({SupportedConstraints}),
otherConstraint CONSTRAINT-TYPE.&Type
({SupportedConstraints}{@otherConstraintType})
}
CONSTRAINT-TYPE ::= TYPE-IDENTIFIER
SupportedConstraints CONSTRAINT-TYPE ::= {...}
Range ::= SEQUENCE {
min [0] OCTET STRING,
max [1] OCTET STRING
}
Validity ::= SEQUENCE {
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start [0] GeneralizedTime OPTIONAL,
end [1] GeneralizedTime OPTIONAL
}
Signature ::= SEQUENCE {
signatureAlgorithm AlgorithmIdentifier,
signature OCTET STRING,
certificates SEQUENCE OF Certificate OPTIONAL
}
END
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Authors' Addresses
Thomas Kunz
Fraunhofer Institute for Secure Information Technology
Rheinstrasse 75
Darmstadt D-64295
Germany
Email: thomas.kunz@sit.fraunhofer.de
Susanne Okunick
Fraunhofer Institute for Secure Information Technology
Rheinstrasse 75
Darmstadt D-64295
Germany
Email: susanne.okunick@sit.fraunhofer.de
Ulrich Pordesch
Fraunhofer Gesellschaft
Rheinstrasse 75
Darmstadt D-64295
Germany
Email: ulrich.pordesch@zv.fraunhofer.de
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Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
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on the procedures with respect to rights in RFC documents can be
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Funding for the RFC Editor function is provided by the IETF
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Kunz, et al. Expires April 17, 2008 [Page 36]
