Internet Draft D. Pinkas
<draft-ietf-pkix-pr-tsa-05.txt> Bull
Target Category: INFORMATIONAL N. Pope
August 2003 Security & Standards
Expires in six months J. Ross
Security & Standards
Policy Requirements for Time-Stamping Authorities
<draft-ietf-pkix-pr-tsa-05.txt>
Status of this Memo
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Copyright (C) The Internet Society (2002). All Rights Reserved.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document defines requirements for a baseline time-stamp policy
for Time-Stamping Authorities (TSAs) issuing time-stamp tokens,
supported by public key certificates, with an accuracy of one
second or better. A TSA may define its own policy which enhances
the policy defined in the current document. Such a policy shall
incorporate or further constrain the requirements identified in the
current document.
Foreword
The contents of this Informational RFC is technically equivalent
to ETSI TS 102 023 V 1.2.1 (2002-06) [TS 102023]. The ETSI TS is
under the ETSI Copyright (C). Individual copies of this ETSI
deliverable can be downloaded from http://www.etsi.org
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Policy Requirements for Time-Stamping Authorities August 2003
Table of Contents
1. Introduction 4
2. Overview 5
3. Definitions and abbreviations 5
3.1. Definitions 5
3.2. Abbreviations 7
4. General concepts 7
4.1. Time-stamping services 7
4.2. Time-stamping authority 7
4.3. Subscriber 8
4.4. Time-stamp policy and TSA practice statement 8
4.4.1. Purpose 8
4.4.2. Level of specificity 8
4.4.3. Approach 9
5. Time-stamp Policies 9
5.1. Overview 9
5.2. Identification 9
5.3. User Community and applicability 10
5.4. Conformance 10
6. Obligations and liability 10
6.1. TSA obligations 10
6.1.1. General 10
6.1.2. TSA obligations towards subscribers 11
6.2. Subscriber obligations 11
6.3. Relying party obligations 11
6.4. Liability 11
7. Requirements on TSA practices 11
7.1. Practice and Disclosure Statements 12
7.1.1. TSA Practice statement 12
7.1.2. TSA disclosure Statement 13
7.2. Key management life cycle 14
7.2.1. TSU key generation 14
7.2.2. TSU private key protection 15
7.2.3. TSU public key Distribution 15
7.2.4. Rekeying TSU's Key 16
7.2.5. End of TSU key life cycle 16
7.2.6. Life cycle management of the cryptographic module
used to sign time-stamps 17
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7.3. Time-stamping 17
7.3.1. Time-stamp token 17
7.3.2. Clock Synchronization with UTC 18
7.4. TSA management and operation 19
7.4.1. Security management 19
7.4.2. Asset classification and management 20
7.4.3. Personnel security 20
7.4.4. Physical and environmental security 22
7.4.5. Operations management 23
7.4.6. System Access Management 24
7.4.7. Trustworthy Systems Deployment and Maintenance 25
7.4.8. Compromise of TSA Services 25
7.4.9. TSA termination 26
7.4.10. Compliance with Legal Requirements 27
7.4.11. Recording of Information Concerning Operation
of Time-stamping Services 27
7.5. Organizational 28
8. Security considerations 29
9. Acknowledgments 30
10. References 30
10.1. Normative References 30
10.2. Non-normative References 30
11. Authors' addresses 31
Annex A (informative): Coordinated Universal Time 33
Annex B (informative): Possible for Implementation Architectures and
Time-Stamping Services 35
Annex C (informative): Long Term Verification of time-stamp tokens 37
Annex D (informative): Model TSA disclosure statement 38
Full Copyright Statement 40
Terminology
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 RFC 2119 [RFC 2119].
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1. Introduction
In creating reliable and manageable digital evidence it becomes
necessary to have an agreed upon method of associating time data to
transaction so that they might be compared to each other at some later
time. The quality of this evidence is based in the process of creating
and managing the data structure that represent the events and the
quality of the parametric data points that anchor them to the real
world. In this instance this being the time data and how it was
applied.
A typical transaction is a digitally signed document, where it is
necessary to prove that the digital signature from the signer was
applied when the signer's certificate was valid.
A timestamp or a time mark (which is an audit record kept in a secure
audit trail from a trusted third party) applied to a digital signature
value proves that the digital signature was created before the date
included in the time-stamp or time mark.
To prove the digital signature was generated while the signer's
certificate was valid, the digital signature must be verified and
the following conditions satisfied:
1. the time-stamp (or time mark) has been applied before the end
of the validity period of the signer's certificate,
2. the time-stamp (or time mark) has been applied either
while the signer's certificate was not revoked or
before the revocation date of the certificate.
Thus a time-stamp (or time mark) applied in this manner proves that the
digital signature was created while the signer's certificate was valid.
This concept can be extended to prove the validity of a digital
signature over the whole of any certificate chain.
Policy requirements to cover that case is the primary reason of the
present document. However, it should be observed that these policy
requirements can be used to address other needs.
The electronic time stamp is gaining an increasing interest by the
business sector and is becoming an important component of electronic
signatures, also featured by the ETSI Electronic Signature Format
standard [TS 101733] or Electronic Signature Formats for long term
electronic signatures [RFC 3126], built upon the Time-Stamp Protocol
[RFC 3161]. Agreed minimum security and quality requirements are
necessary in order to ensure trustworthy validation of long-term
electronic signatures.
The European Directive 1999/93/EC [Dir 99/93/EC] defines certification
service provider as "an entity or a legal or natural person who issues
certificates or provides other services related to electronic
signatures". One example of a certification-service-provider is a
Time-Stamping Authority.
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2. Overview
These policy requirements are primarily aimed at time-stamping services
used in support of qualified electronic signatures (i.e. in line with
article 5.1 of the European Directive on a community framework for
electronic signatures) but may be applied to any application requiring
to prove that a datum existed before a particular time.
These policy requirements are based upon the use of public key
cryptography, public key certificates and reliable time sources.
The present document may be used by independent bodies as the basis for
confirming that a TSA may be trusted for providing time-stamping
services.
The current document addresses requirements for TSAs issuing time-stamp
tokens which are synchronized with Coordinated universal time (UTC) and
digitally signed by TSUs.
Subscriber and relying parties should consult the TSA's practice
statement to obtain further details of precisely how this time-stamp
policy is implemented by the particular TSA (e.g. protocols used in
providing this service).
The current document does not specify:
- protocols used to access the TSUs;
NOTE 1: A time-stamping protocol is defined in RFC 3161 [RFC 3161] and
profiled in TS 101 861 [TS 101861].
- how the requirements identified herein may be assessed by an
independent body;
- requirements for information to be made available to such
independent bodies;
- requirements on such independent bodies.
NOTE 2: See CEN Workshop Agreement 14172 "EESSI Conformity Assessment
Guidance" [CWA 14172].
3. Definitions and abbreviations
3.1. Definitions
For the purposes of the present document, the following terms and
definitions apply:
NOTE: Where a definition is copied from a referenced document this is
indicated by inclusion of the reference identifier number at the end of
the definition.
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relying party: recipient of a time-stamp token who relies on that
time-stamp token.
subscriber: entity requiring the services provided by a TSA and which
has explicitly or implicitly agreed to its terms and conditions.
time-stamp token: data object that binds a representation of a datum to
a particular time, thus establishing evidence that the datum existed
before that time.
time-stamping authority: authority which issues time-stamp tokens.
TSA Disclosure statement: set of statements about the policies and
practices of a TSA that particularly require emphasis or disclosure to
subscribers and relying parties, for example to meet regulatory
requirements.
TSA practice statement: statement of the practices that a TSA employs
in issuing time-stamp tokens.
TSA system: composition of IT products and components organized to
support the provision of time-stamping services.
time-stamp policy: named set of rules that indicates the applicability
of a time-stamp token to a particular community and/or class of
application with common security requirements.
time-stamping unit: set of hardware and software which is managed as a
unit and has a single time-stamp token signing key active at a time.
Coordinated Universal Time (UTC): Time scale based on the second as
defined in ITU-R Recommendation TF.460-5 [TF.460-5].
NOTE: For most practical purposes UTC is equivalent to mean solar time
at the prime meridian. More specifically, UTC is a compromise
between the highly stable atomic time (Temps Atomique International
- TAI) and solar time derived from the irregular Earth rotation
(related to the Greenwich mean sidereal time (GMST) by a conventional
relationship). (See annex A for more details).
UTC(k): Time-scale realized by the laboratory "k" and kept in close
agreement with UTC, with the goal to reach plus or minus 100 ns.
(See ITU-R Recommendation TF.536-1 [TF.536-1]).
NOTE: A list of UTC(k) laboratories is given in section 1 of
Circular T disseminated by BIPM and available from the BIPM website
(http://www.bipm.org/).
3.2. Abbreviations
For the purposes of the present document, the following abbreviations
apply:
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TSA Time-Stamping Authority
TSU Time-Stamping Unit
TST Time-Stamp Token
UTC Coordinated Universal Time
4. General concepts
4.1 Time-stamping services
The provision of time-stamping services is broken down in the present
document into the following component services for the purposes of
classifying requirements:
- Time-stamping provision: This service component generates
time-stamp tokens.
- Time-stamping management: The service component that monitors and
controls the operation of the time-stamping services to ensure
that the service provided is as specified by the TSA. This service
component has responsibility for the installation and
de-installation of the time-stamping provision service.
For example, time-stamping management ensures that the clock used
for time-stamping is correctly synchronized with UTC.
This subdivision of services is only for the purposes of clarifying
the requirements specified in the current document and places no
restrictions on any subdivision of an implementation of time-stamping
services.
4.2 Time-stamping authority
The authority trusted by the users of the time-stamping services (i.e.
subscribers as well as relying parties) to issue time-stamp tokens is
called the Time-Stamping Authority (TSA). The TSA has overall
responsibility for the provision of the time-stamping services
identified in clause 4.1. The TSA has responsibility for the operation
of one or more TSU's which creates and signs on behalf of the TSA. The
TSA responsible for issuing a time-stamp token is identifiable (see
7.3.1 h).
The TSA may make use of other parties to provide parts of the
Time-Stamping Services. However, the TSA always maintains overall
responsibility and ensures that the policy requirements identified in
the present document are met. For example, a TSA may sub-contract all
the component services, including the services which generate
time-stamp tokens using the TSU's keys. However, the private key or
keys used to generate the time-stamp tokens are identified as
belonging to the TSA which maintains overall responsibility for
meeting the requirements defined in the current document.
A TSA may operate several identifiable time-stamping units. Each unit
has a different key. See Annex B for possible implementations.
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A TSA is a certification-service-provider, as defined in the EU
Directive on Electronic Signatures (see article 2(11)), which issues
time-stamp tokens.
4.3 Subscriber
The subscriber may be an organization comprising several end-users or
an individual end-user.
When the subscriber is an organization, some of the obligations that
apply to that organization will have to apply as well to the end-users.
In any case the organization will be held responsible if the
obligations from the end-users are not correctly fulfilled and
therefore the such an organization is expected to suitably inform its
end users.
When the subscriber is an end-user, the end-user will be held directly
responsible if its obligations are not correctly fulfilled.
4.4 Time-stamp policy and TSA practice statement
This section explains the relative roles of Time-stamp policy and TSA
practice statement. It places no restriction on the form of a
time-stamp policy or practice statement specification.
4.4.1 Purpose
In general, the time-stamp policy states "what is to be adhered to,"
while a TSA practice statement states "how it is adhered to", i.e., the
processes it will use in creating time-stamps and maintaining the
accuracy of its clock. The relationship between the time-stamp policy
and TSA practice statement is similar in nature to the relationship of
other business policies which state the requirements of the business,
while operational units define the practices and procedures of how
these policies are to be carried out.
The present document specifies a time-stamp policy to meet general
requirements for trusted time-stamping services. TSAs specify in TSA
practice statements how these requirements are met.
4.4.2 Level of specificity
A time-stamp policy is a less specific document than a TSA practice
statement. A TSA practice statement is a more detailed description of
the terms and conditions as well as business and operational practices
of a TSA in issuing and otherwise managing time-stamping services. The
TSA practice statement of a TSA enforces the rules established by a
time-stamp policy. A TSA practice statement defines how a specific TSA
meets the technical, organizational and procedural requirements
identified in a time-stamp policy.
NOTE: Even lower-level internal documentation may be appropriate for a
TSA detailing the specific procedures necessary to complete the
practices identified in the TSA practice statement.
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4.4.3 Approach
The approach of a time-stamp policy is significantly different from a
TSA practice statement. A time-stamp policy is defined independently of
the specific details of the specific operating environment of a TSA,
whereas a TSA practice statement is tailored to the organizational
structure, operating procedures, facilities, and computing environment
of a TSA. A time-stamp policy may be defined by the user of times-stamp
services, whereas the TSA practice statement is always defined by the
provider.
5 Time-stamp Policies
5.1 Overview
A time-stamp policy is a "named set of rules that indicates the
applicability of a time-stamp token to a particular community and/or
class of application with common security requirements" (see clauses
3.1 and 4.4).
The present document defines requirements for a baseline time-stamp
policy for TSAs issuing time-stamp tokens, supported by public key
certificates, with an accuracy of 1 second or better.
NOTE 1: Without additional measures the relying party may not be able
to ensure the validity of a time-stamp token beyond the end of the
validity period of the supporting certificate. See annex C on
verification of the validity of a time-stamp token beyond the validity
period of the TSU's certificate.
A TSA may define its own policy which enhances the policy defined in
the current document. Such a policy shall incorporate or further
constrain the requirements identified in the current document.
If an accuracy of better than 1 second is provided by a TSA then, if
all the TSUs have that same characteristics, the accuracy shall be
indicated in the TSA's disclosure statement (see section 7.1.2)
otherwise in each time-stamp token issued with an accuracy of
better than 1 second.
NOTE 2: It is required that a time-stamp token includes an identifier
for the applicable policy (see section 7.3.1).
5.2 Identification
The object-identifier [X.208] of the baseline time-stamp policy is:
itu-t(0) identified-organization(4) etsi(0) time-stamp-policy(2023)
policy-identifiers(1) baseline-ts-policy (1)
A TSA shall also include the identifier for the time-stamp policy being
supported in the TSA disclosure statement made available to subscribers
and relying parties to indicate its claim of conformance.
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5.3 User Community and applicability
This policy is aimed at meeting the requirements of time-stamping
qualified electronic signatures (see European Directive on Electronic
Signatures) for long term validity (e.g. as defined in TS 101 733
[TS 101733]) but is generally applicable to any use which has a
requirement for equivalent quality.
This policy may be used for public time-stamping services or
time-stamping services used within a closed community.
5.4 Conformance
The TSA shall use the identifier for the time-stamp policy in
time-stamp tokens as given in section 5.2, or define its own time-stamp
policy that incorporates or further constrains the requirements
identified in the present document:
a) if the TSA claims conformance to the identified time-stamp policy
and makes available to subscribers and relying parties on request the
evidence to support the claim of conformance; or
b) if the TSA has been assessed to be conformant to the identified
time-stamp policy by an independent party.
A conformant TSA must demonstrate that:
a) it meets its obligations as defined in section 6.1;
b) it has implemented controls which meet the requirements specified in
section 7.
6 Obligations and liability
6.1 TSA obligations
6.1.1 General
The TSA shall ensure that all requirements on TSA, as detailed in
section 7, are implemented as applicable to the selected trusted
time-stamp policy.
The TSA shall ensure conformance with the procedures prescribed in this
policy, even when the TSA functionality is undertaken by
sub-contractors.
The TSA shall also ensure adherence to any additional obligations
indicated in the time-stamp either directly or incorporated by
reference.
The TSA shall provide all its time-stamping services consistent with
its practice statement.
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6.1.2 TSA obligations towards subscribers
The TSA shall meet its claims as given in its terms and conditions
including the availability and accuracy of its service.
6.2 Subscriber obligations
The current document places no specific obligations on the subscriber
beyond any TSA specific requirements stated in the TSA's terms and
condition.
NOTE: It is advisable that, when obtaining a time-stamp token, the
subscriber verifies that the time-stamp token has been correctly signed
and that the private key used to sign the time-stamp token has not been
compromised.
6.3 Relying party obligations
The terms and conditions made available to relying parties (see section
7.1.2) shall include an obligation on the relying party that, when
relying on a time-stamp token, it shall:
a) verify that the time-stamp token has been correctly signed and that
the private key used to sign the time-stamp has not been compromised
until the time of the verification;
NOTE: During the TSU's certificate validity period, the validity of the
signing key can be checked using current revocation status for the
TSU's certificate. If the time of verification exceeds the end of the
validity period of the corresponding certificate, see annex C for
guidance.
b) take into account any limitations on the usage of the time-stamp
indicated by the time-stamp policy;
c) take into account any other precautions prescribed in agreements or
elsewhere.
6.4 Liability
The present document does not specify any requirement on liability. In
particular, it should be noticed that a TSA may disclaim or limit any
liability unless otherwise stipulated by the applicable law.
7 Requirements on TSA practices
The TSA shall implement the controls that meet the following
requirements.
These policy requirements are not meant to imply any restrictions on
charging for TSA services.
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The requirements are indicated in terms of the security objectives
followed by more specific requirements for controls to meet those
objectives where considered necessary to provide the necessary
confidence that those objective will be met.
NOTE: The details of controls required to meet an objective is a
balance between achieving the necessary confidence whilst minimizing
the restrictions on the techniques that a TSA may employ in issuing
time-stamp tokens. In case of section 7.4 (TSA management and
operation) reference is made to other more general standards which may
be used as a source of more detailed control requirements. Due to these
factors the specificity of the requirements given under a given topic
may vary.
The provision of a time-stamp token in response to a request is at the
discretion of the TSA depending on any service level agreements with
the subscriber.
7.1 Practice and Disclosure Statements
7.1.1 TSA Practice statement
The TSA shall ensure that it demonstrates the reliability necessary for
providing time-stamping services.
In particular:
a) The TSA shall have a risk assessment carried out in order to
evaluate business assets and threats to those assets in order to
determine the necessary security controls and operational procedures.
b) The TSA shall have a statement of the practices and procedures used
to address all the requirements identified in this time-stamp policy.
NOTE 1: This policy makes no requirement as to the structure of the TSA
practice statement.
c) The TSA's practice statement shall identify the obligations of all
external organizations supporting the TSA services including the
applicable policies and practices.
d) The TSA shall make available to subscribers and relying parties its
practice statement, and other relevant documentation, as necessary to
assess conformance to the time-stamp policy.
NOTE 2: The TSA is not generally required to make all the details of
its practices public.
e) The TSA shall disclose to all subscribers and potential relying
parties the terms and conditions regarding use of its time-stamping
services as specified in section 7.1.2.
f) The TSA shall have a high level management body with final authority
for approving the TSA practice statement.
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g) The senior management of the TSA shall ensure that the practices are
properly implemented.
h) The TSA shall define a review process for the practices including
responsibilities for maintaining the TSA practice statement.
i) The TSA shall give due notice of changes it intends to make in its
practice statement and shall, following approval as in (f) above, make
the revised TSA practice statement immediately available as required
under (d) above.
7.1.2 TSA disclosure Statement
The TSA shall disclose to all subscribers and potential relying parties
the terms and conditions regarding use of its time-stamping services.
This statement shall at least specify for each time-stamp policy
supported by the TSA:
a) The TSA contact information.
b) The time-stamp policy being applied.
c) At least one hashing algorithm which may be used to represent the
datum being time-stamped. (No hash algorithm is mandated).
d) The expected life-time of the signature used to sign the time-stamp
token (depends on the hashing algorithm being used, the signature
algorithm being used and the private key length).
e) The accuracy of the time in the time-stamp tokens with respect to
UTC.
f) Any limitations on the use of the time-stamping service.
g) The subscriber's obligations as defined in section 6.2, if any.
h) The relying party's obligations as defined in section 6.3.
i) Information on how to verify the time-stamp token such that the
relying party is considered to "reasonably rely" on the time-stamp
token (see section 6.3) and any possible limitations on the validity
period.
j) The period of time during which TSA event logs (see section 7.4.10)
are retained.
k) The applicable legal system, including any claim to meet the
requirements on time-stamping services under national law.
l) Limitations of liability.
m) Procedures for complaints and dispute settlement.
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n) If the TSA has been assessed to be conformant with the identified
time-stamp policy, and if so by which independent body.
NOTE 1: It is also recommended that the TSA includes in its
time-stamping disclosure statement availability of its service, for
example the expected mean time between failure of the time-stamping
service, the mean time to recovery following a failure and provisions
made for disaster recovery including back-up services;
This information shall be available through a durable means of
communication. This information shall be available in a readily
understandable language. It may be transmitted electronically.
NOTE 2: A model TSA disclosure statement which may be used as the basis
of such a communication is given in annex D. Alternatively this may be
provided as part of a subscriber / relying party agreement. These TSA
disclosure statement may be included in a TSA practice statement
provided that they are conspicuous to the reader.
7.2 Key management life cycle
7.2.1 TSA key generation
The TSA shall ensure that any cryptographic keys are generated in under
controlled circumstances.
In particular:
a) The generation of the TSU's signing key(s) shall be undertaken in a
physically secured environment (see section 7.4.4) by personnel in
trusted roles (see section 7.4.3) under, at least, dual control. The
personnel authorized to carry out this function shall be limited to
those requiring to do so under the TSA's practices.
b) The generation of the TSU's signing key(s) shall be carried out
within a cryptographic module(s) which either:
- meets the requirements identified in FIPS 140-1 [FIPS 140-1]
level 3 or higher, or
- meets the requirements identified in CEN Workshop Agreement
14167-2 [CWA 14167-2], or
- is a trustworthy system which is assured to EAL 4 or higher in
accordance to ISO 15408 [ISO 15408], or equivalent security
criteria. This shall be to a security target or protection
profile which meets the requirements of the current document,
based on a risk analysis and taking into account physical and
other non-technical security measures.
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c) The TSU key generation algorithm, the resulting signing key length
and signature algorithm used for signing time-stamp tokens key shall be
recognized by any national supervisory body, or in accordance with
existing current state of art, as being fit for the purposes of
time-stamp tokens as issued by the TSA.
7.2.2 TSU private key protection
The TSA shall ensure that TSU private keys remain confidential and
maintain their integrity.
In particular:
a) The TSU private signing key shall be held and used within a
cryptographic module which:
- meets the requirements identified in FIPS 140-1 [FIPS 140-1] level 3
or higher; or
- meets the requirements identified in CEN Workshop Agreement
14167-2 [CWA 14167-2]; or
- is a trustworthy system which is assured to EAL 4 or higher in
accordance to ISO 15408 [ISO 15408], or equivalent security criteria.
This shall be to a security target or protection profile which meets
the requirements of the current document, based on a risk analysis
and taking into account physical and other non-technical security
measures.
NOTE: Backup of TSU private keys is deprecated in order to minimize
risk of key compromise.
b) If TSU private keys are backed up, they shall be copied, stored
and recovered only by personnel in trusted roles using, at least, dual
control in a physically secured environment. (see section 7.4.4). The
personnel authorized to carry out this function shall be limited to
those requiring to do so under the TSA's practices.
c) Any backup copies of the TSU private signing keys shall be protected
to ensure its confidentiality by the cryptographic module before being
stored outside that device.
7.2.3 TSU public key Distribution
The TSA shall ensure that the integrity and authenticity of the TSU
signature verification (public) keys and any associated parameters are
maintained during its distribution to relying parties.
In particular:
a) TSU signature verification (public) keys shall be made available to
relying parties in a public key certificate.
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NOTE: For example, TSU's certificates may be issued by a certification
authority operated by the same organization as the TSA, or issued by
another authority.
b) The TSU's signature verification (public) key certificate shall be
issued by a certification authority operating under a certificate
policy which provides a level of security equivalent to, or higher
than, this time-stamping policy.
7.2.4 Rekeying TSU's Key
The life-time of TSU's certificate shall be not longer than the period
of time that the chosen algorithm and key length is recognized as being
fit for purpose (see section 7.2.1c)).
NOTE 1: The following additional considerations apply when limiting
that lifetime:
- Section 7.4.10 requires that records concerning time-stamping
services shall be held for a period of time as appropriate for at
least 1 year after the expiration of the validity of the TSU's
signing keys. The longer the validity period of the TSU certificates
will be, the longer the size of the records to be kept will be.
- Should a TSU private key be compromised, then the longer the
life-time, the more affected time-stamp tokens there will be.
NOTE 2: TSU key compromise does not only depend on the characteristics
of the cryptographic module being used but also on the procedures being
used at system initialization and key export (when that function is
supported).
7.2.5 End of TSU key life cycle
The TSA shall ensure that TSU private signing keys are not used beyond
the end of their life cycle.
In particular:
a) Operational or technical procedures shall be in place to ensure that
a new key is put in place when a TSU's key expires.
b) The TSU private signing keys, or any key part, including any copies
shall be destroyed such that the private keys cannot be retrieved.
c) The TST generation system SHALL reject any attempt to issue TSTs if
the signing private key has expired.
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7.2.6 Life cycle management of the cryptographic module used to sign
time-stamps
The TSA shall ensure the security of cryptographic hardware throughout
its lifecycle.
In particular the TSA shall ensure that:
a) Time-stamp token signing cryptographic hardware is not tampered with
during shipment;
b) Time-stamp token signing cryptographic hardware is not tampered with
while stored;
c) Installation, activation and duplication of TSU's signing keys in
cryptographic hardware shall be done only by personnel in trusted roles
using, at least, dual control in a physically secured environment.
(see section 7.4.4);
d) Time-stamp token signing cryptographic hardware is functioning
correctly; and
e) TSU private signing keys stored on TSU cryptographic module are
erased upon device retirement.
7.3 Time-stamping
7.3.1 Time-stamp token
The TSA shall ensure that time-stamp tokens are issued securely and
include the correct time.
In particular:
a) The time-stamp token shall include an identifier for the time-stamp
policy;
b) Each time-stamp token shall have a unique identifier;
c) The time values the TSU uses in the time-stamp token shall be
traceable to at least one of the real time values distributed by a
UTC(k) laboratory.
NOTE 1: The Bureau International des Poids et Mesures (BIPM) computes
UTC on the basis of its local representations UTC(k) from a large
ensemble of atomic clocks in national metrology institutes and national
astronomical observatories round the world. The BIPM disseminates UTC
through its monthly Circular T [list 1]. This is available on the BIPM
website (www.bipm.org) and it officially identifies all those
institutes having recognized UTC(k) time scales.
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d) The time included in the time-stamp token shall be synchronized with
UTC within the accuracy defined in this policy and, if present, within
the accuracy defined in the time-stamp token itself;
e) If the time-stamp provider's clock is detected (see section 7.3.2c))
as being out of the stated accuracy (see section 7.1.2e)) then
time-stamp tokens shall not be issued.
f) The time-stamp token shall include a representation (e.g. hash
value) of the datum being time-stamped as provided by the requestor;
g) The time-stamp token shall be signed using a key generated
exclusively for this purpose.
NOTE 2: A protocol for a time-stamp token is defined in RFC 3631 and
profiled in TS 101 861 [TS 101861].
NOTE 3: In the case of a number of requests at approximately the same
time, the ordering of the time within the accuracy of the TSU clock is
not mandated.
h) The time-stamp token shall include:
- where applicable, an identifier for the country in which the TSA
is established;
- an identifier for the TSA;
- an identifier for the unit which issues the time-stamps.
7.3.2 Clock Synchronization with UTC
The TSA shall ensure that its clock is synchronized with UTC within the
declared accuracy.
In particular:
a) The calibration of the TSU clocks shall be maintained such that the
clocks shall not be expected to drift outside the declared accuracy.
b) The TSU clocks shall be protected against threats which could result
in an undetected change to the clock that takes it outside its
calibration.
NOTE 1: Threats may include tampering by unauthorized personnel, radio
or electrical shocks.
c) The TSA shall ensure that, if the time that would be indicated in a
time-stamp token drifts or jumps out of synchronization with UTC, this
will be detected (see also 7.3.1e)).
NOTE 2: Relying parties are required to be informed of such events
(see section 7.4.8).
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d) The TSA shall ensure that clock synchronization is maintained when a
leap second occurs as notified by the appropriate body. The change to
take account of the leap second shall occur during the last minute of
the day when the leap second is scheduled to occur. A record shall be
maintained of the exact time (within the declared accuracy) when this
change occurred. See annex A for more details.
NOTE 3: A leap second is an adjustment to UTC by skipping or adding an
extra second on the last second of a UTC month. First preference is
given to the end of December and June, and second preference is given
to the end of March and September.
7.4 TSA management and operation
7.4.1 Security management
The TSA shall ensure that administrative and management procedures are
applied which are adequate and correspond to recognized best practice.
In particular:
TSA General
a) The TSA shall retain responsibility for all aspects of the provision
of time-stamping services within the scope of this time-stamp policy,
whether or not functions are outsourced to subcontractors.
Responsibilities of third parties shall be clearly defined by the TSA
and appropriate arrangements made to ensure that third parties are
bound to implement any controls required by the TSA. The TSA shall
retain responsibility for the disclosure of relevant practices of all
parties.
b) The TSA management shall provide direction on information security
through a suitable high level steering forum that is responsible for
defining the TSA's information security policy. The TSA shall ensure
publication and communication of this policy to all employees who are
impacted by it.
c) The information security infrastructure necessary to manage the
security within the TSA shall be maintained at all times. Any changes
that will impact on the level of security provided shall be approved by
the TSA management forum.
NOTE 1: See ISO/IEC 17799 [ISO 17799] for guidance on information
security management including information security infrastructure,
management information security forum and information security
policies.
d) The security controls and operating procedures for TSA facilities,
systems and information assets providing the time-stamping services
shall be documented, implemented and maintained.
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NOTE 2: The present documentation (commonly called a system security
policy or manual) should identify all relevant targets, objects and
potential threats related to the services provided and the safeguards
required to avoid or limit the effects of those threats, consistent
with the Risk Assessment required under section 7.1.1a). It should
describe the rules, directives and procedures regarding how the
specified services and the associated security assurance are granted in
addition to stating policy on incidents and disasters.
e) TSA shall ensure that the security of information is maintained when
the responsibility for TSA functions has been outsourced to another
organization or entity.
7.4.2 Asset classification and management
The TSA shall ensure that its information and other assets receive an
appropriate level of protection.
In particular:
- The TSA shall maintain an inventory of all assets and shall assign a
classification for the protection requirements to those assets
consistent with the risk analysis.
7.4.3 Personnel security
The TSA shall ensure that personnel and hiring practices enhance and
support the trustworthiness of the TSA's operations.
In particular (TSA general):
a) The TSA shall employ personnel which possess the expert knowledge,
experience and qualifications necessary for the offered services and as
appropriate to the job function.
NOTE 1: TSA personnel should be able to fulfil the requirement of
"expert knowledge, experience and qualifications" through formal
training and credentials, actual experience, or a combination of the
two.
NOTE 2: Personnel employed by a TSA include individual personnel
contractually engaged in performing functions in support of the TSA's
time-stamping services. Personnel who may be involved in monitoring the
TSA services need not be TSA personnel.
b) Security roles and responsibilities, as specified in the TSA's
security policy, shall be documented in job descriptions. Trusted
roles, on which the security of the TSA's operation is dependent, shall
be clearly identified.
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c) TSA personnel (both temporary and permanent) shall have job
descriptions defined from the view point of separation of duties and
least privilege, determining position sensitivity based on the duties
and access levels, background screening and employee training and
awareness. Where appropriate, these shall differentiate between general
functions and TSA specific functions. These should include skills and
experience requirements.
d) Personnel shall exercise administrative and management procedures
and processes that are in line with the TSA's information security
management procedures (see section 7.4.1).
NOTE 3: See ISO/IEC 17799 [ISO 17799] for guidance.
The following additional controls shall be applied to time-stamping
management:
e) Managerial personnel shall be employed who possess:
- knowledge of time-stamping technology; and
- knowledge of digital signature technology; and
- knowledge of mechanisms for calibration or synchronization the
TSU clocks with UTC; and
- familiarity with security procedures for personnel with security
responsibilities; and
- experience with information security and risk assessment.
f) All TSA personnel in trusted roles shall be free from conflict of
interest that might prejudice the impartiality of the TSA operations.
g) Trusted roles include roles that involve the following
responsibilities:
- Security Officers: Overall responsibility for administering the
implementation of the security practices.
- System Administrators: Authorized to install, configure and
maintain the TSA trustworthy systems for time-stamping management.
- System Operators: Responsible for operating the TSA trustworthy
systems on a day-to-day basis. Authorized to perform system backup
and recovery.
- System Auditors: Authorized to view archives and audit logs of
the TSA trustworthy systems.
h) TSA personnel shall be formally appointed to trusted roles by senior
management responsible for security.
i) The TSA shall not appoint to trusted roles or management any person
who is known to have a conviction for a serious crime or other offence
which affects his/her suitability for the position. Personnel shall not
have access to the trusted functions until any necessary checks are
completed.
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NOTE 4: In some countries it may not be possible for TSA to obtain
information on past convictions without the collaboration of the
candidate employee.
7.4.4 Physical and environmental security
The TSA shall ensure that physical access to critical services is
controlled and physical risks to its assets minimized.
In particular (general):
a) For both the time-stamping provision and the time-stamping
management:
- physical access to facilities concerned with time-stamping services
shall be limited to properly authorized individuals;
- controls shall be implemented to avoid loss, damage or compromise of
assets and interruption to business activities; and
- controls shall be implemented to avoid compromise or theft of
information and information processing facilities.
b) Access controls shall be applied to the cryptographic module to meet
the requirements of security of cryptographic modules as identified in
clauses 7.2.1 and 7.2.2.
c) The following additional controls shall be applied to time-stamping
management:
- The time-stamping management facilities shall be operated in an
environment which physically protects the services from compromise
through unauthorized access to systems or data.
- Physical protection shall be achieved through the creation of
clearly defined security perimeters (i.e. physical barriers) around
the time-stamping management. Any parts of the premises shared with
other organizations shall be outside this perimeter.
- Physical and environmental security controls shall be implemented to
protect the facility that houses system resources, the system
resources themselves, and the facilities used to support their
operation. The TSA's physical and environmental security policy for
systems concerned with time-stamping management shall address as a
minimum the physical access control, natural disaster protection,
fire safety factors, failure of supporting utilities (e.g. power,
telecommunications), structure collapse, plumbing leaks, protection
against theft, breaking and entering, and disaster recovery.
- Controls shall be implemented to protect against equipment,
information, media and software relating to the time-stamping
services being taken off-site without authorization.
NOTE 1: See ISO/IEC 17799 [ISO 17799] for guidance on physical and
environmental security.
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NOTE 2: Other functions may be supported within the same secured area
provided that the access is limited to authorized personnel.
7.4.5 Operations management
The TSA shall ensure that the TSA system components are secure and
correctly operated, with minimal risk of failure:
In particular (general):
a) The integrity of TSA system components and information shall be
protected against viruses, malicious and unauthorized software.
b) Incident reporting and response procedures shall be employed in such
a way that damage from security incidents and malfunctions shall be
minimized.
c) Media used within the TSA trustworthy systems shall be securely
handled to protect media from damage, theft, unauthorized access and
obsolescence.
NOTE 1: Every member of personnel with management responsibilities is
responsible for planning and effectively implementing the time-stamp
policy and associated practices as documented in the TSA practice
statement.
d) Procedures shall be established and implemented for all trusted and
administrative roles that impact on the provision of time-stamping
services.
Media handling and security
e) All media shall be handled securely in accordance with requirements
of the information classification scheme (see section 7.4.2). Media
containing sensitive data shall be securely disposed of when no longer
required.
System Planning
f) Capacity demands shall be monitored and projections of future
capacity requirements made to ensure that adequate processing power and
storage are available.
Incident reporting and response
g) The TSA shall act in a timely and coordinated manner in order to
respond quickly to incidents and to limit the impact of breaches of
security. All incidents shall be reported as soon as possible after the
incident.
The following additional controls shall be applied to time-stamping
management:
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Operations procedures and responsibilities
h) TSA security operations shall be separated from other operations.
NOTE 2: TSA security operations' responsibilities include:
- operational procedures and responsibilities;
- secure systems planning and acceptance;
- protection from malicious software;
- housekeeping;
- network management;
- active monitoring of audit journals, event analysis and follow-up;
- media handling and security;
- data and software exchange.
These operations shall be managed by TSA trusted personnel, but, may
actually be performed by, non-specialist, operational personnel (under
supervision), as defined within the appropriate security policy, and,
roles and responsibility documents.
7.4.6 System Access Management
The TSA shall ensure that TSA system access is limited to properly
authorized individuals.
In particular (general):
a) Controls (e.g., firewalls) shall be implemented to protect the TSA's
internal network domains from unauthorized access including access by
subscribers and third parties.
NOTE 1: Firewalls should also be configured to prevent all protocols
and accesses not required for the operation of the TSA.
b) The TSA shall ensure effective administration of user (this includes
operators, administrators and auditors) access to maintain system
security, including user account management, auditing and timely
modification or removal of access.
c) The TSA shall ensure that access to information and application
system functions is restricted in accordance with the access control
policy and that the TSA system provides sufficient computer security
controls for the separation of trusted roles identified in TSA's
practices, including the separation of security administrator and
operation functions. Particularly, use of system utility programs is
restricted and tightly controlled.
d) TSA personnel shall be properly identified and authenticated before
using critical applications related to time-stamping.
e) TSA personnel shall be accountable for their activities, for example
by retaining event logs (see section 7.4.10).
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The following additional controls shall be applied to time-stamping
management:
f) The TSA shall ensure that local network components (e.g. routers)
are kept in a physically secure environment and that their
configurations are periodically audited for compliance with the
requirements specified by the TSA.
g) Continuous monitoring and alarm facilities shall be provided to
enable the TSA to detect, register and react in a timely manner upon
any unauthorized and/or irregular attempts to access its resources.
NOTE 2: This may use, for example, an intrusion detection system,
access control monitoring and alarm facilities.
7.4.7 Trustworthy Systems Deployment and Maintenance
The TSA shall use trustworthy systems and products that are protected
against modification.
NOTE: The risk analysis carried out on the TSA's services (see section
7.1.1) should identify its critical services requiring trustworthy
systems and the levels of assurance required.
In particular:
a) An analysis of security requirements shall be carried out at the
design and requirements specification stage of any systems development
project undertaken by the TSA or on behalf of the TSA to ensure that
security is built into IT systems.
b) Change control procedures shall be applied for releases,
modifications and emergency software fixes of any operational software.
7.4.8 Compromise of TSA Services
The TSA shall ensure in the case of events which affect the security of
the TSA's services, including compromise of TSU's private signing keys
or detected loss of calibration, that relevant information is made
available to subscribers and relying parties.
In particular:
a) The TSA's disaster recovery plan shall address the compromise or
suspected compromise of TSU's private signing keys or loss of
calibration of a TSU clock, which may have affected time-stamp tokens
which have been issued.
b) In the case of a compromise, or suspected compromise or loss of
calibration the TSA shall make available to all subscribers and relying
parties a description of compromise that occurred.
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c) In the case of compromise to a TSU's operation (e.g. TSU key
compromise), suspected compromise or loss of calibration the TSU shall
not issue time-stamp tokens until steps are taken to recover from the
compromise
d) In case of major compromise of the TSA's operation or loss of
calibration, wherever possible, the TSA shall make available to all
subscribers and relying parties information which may be used to
identify the time-stamp tokens which may have been affected, unless
this breaches the privacy of the TSAs users or the security of the TSA
services.
NOTE: In case the private key does become compromised, an audit trail
of all tokens generated by the TSA may provide a means to discriminate
between genuine and false backdated tokens. Two time-stamp tokens from
two different TSAs may be another way to address this issue.
7.4.9 TSA termination
The TSA shall ensure that potential disruptions to subscribers and
relying parties are minimized as a result of the cessation of the TSA's
time-stamping services, and in particular ensure continued maintenance
of information required to verify the correctness of time-stamp tokens.
In particular:
a) Before the TSA terminates its time-stamping services the following
procedures shall be executed as a minimum:
- the TSA shall make available to all subscribers and relying
parties information concerning its termination;
- TSA shall terminate authorization of all subcontractors to act on
behalf of the TSA in carrying out any functions relating to the
process of issuing time-stamp tokens;
- the TSA shall transfer obligations to a reliable party for
maintaining event log and audit archives (see section 7.4.10)
necessary to demonstrate the correct operation of the TSA for a
reasonable period;
- the TSA shall maintain or transfer to a reliable party its
obligations to make available its public key or its certificates to
relying parties for a reasonable period;
- TSU private keys, including backup copies, shall be destroyed in
a manner such that the private keys cannot be retrieved.
b) The TSA shall have an arrangement to cover the costs to fulfil these
minimum requirements in case the TSA becomes bankrupt or for other
reasons is unable to cover the costs by itself.
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c) The TSA shall state in its practices the provisions made for
termination of service. This shall include:
- notification of affected entities;
- transferring the TSA obligations to other parties.
d) The TSA shall take steps to have the TSU's certificates revoked.
7.4.10 Compliance with Legal Requirements
The TSA shall ensure compliance with legal requirements.
In particular:
a) The TSA shall ensure that the requirements of the European data
protection Directive [Dir 95/46/EC], as implemented through national
legislation, are met.
b) Appropriate technical and organizational measures shall be taken
against unauthorized or unlawful processing of personal data and
against accidental loss or destruction of, or damage to, personal data.
c) The information contributed by users to the TSA shall be completely
protected from disclosure unless with their agreement or by court order
or other legal requirement.
7.4.11 Recording of Information Concerning Operation of Time-stamping
Services
The TSA shall ensure that all relevant information concerning the
operation of time-stamping services is recorded for a defined period of
time, in particular for the purpose of providing evidence for the
purposes of legal proceedings.
In particular:
General
a) The specific events and data to be logged shall be documented by the
TSA.
b) The confidentiality and integrity of current and archived records
concerning operation of time-stamping services shall be maintained.
c) Records concerning the operation of time-stamping services shall be
completely and confidentially archived in accordance with disclosed
business practices.
d) Records concerning the operation of time-stamping services shall be
made available if required for the purposes of providing evidence of
the correct operation of the time-stamping services for the purpose of
legal proceedings.
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e) The precise time of significant TSA environmental, key management
and clock synchronization events shall be recorded.
f) Records concerning time-stamping services shall be held for a period
of time after the expiration of the validity of the TSU's signing keys
as appropriate for providing necessary legal evidence and as notified
in the TSA disclosure statement (see section 7.1.2).
g) The events shall be logged in a way that they cannot be easily
deleted or destroyed (except if reliably transferred to long-term
media) within the period of time that they are required to be held.
NOTE: This may be achieved, for example, through the use of write-only
media, a record of each removable media used and the use of off-site
backup.
h) Any information recorded about subscribers shall be kept
confidential except as where agreement is obtained from the subscriber
for its wider publication.
TSU key management
i) Records concerning all events relating to the life-cycle of TSU keys
shall be logged.
j) Records concerning all events relating to the life-cycle of TSU
certificates (if appropriate) shall be logged.
Clock Synchronization
k) Records concerning all events relating to synchronization of a
TSU's clock to UTC shall be logged. This shall include information
concerning normal re-calibration or synchronization of clocks use in
time-stamping.
l) Records concerning all events relating to detection of loss of
synchronization shall be logged.
7.5 Organizational
The TSA shall ensure that its organization is reliable.
In particular that:
a) Policies and procedures under which the TSA operates shall be
non-discriminatory.
b) The TSA shall make its services accessible to all applicants whose
activities fall within its declared field of operation and that agree
to abide by their obligations as specified in the TSA disclosure
statement.
c) The TSA is a legal entity according to national law.
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d) The TSA has a system or systems for quality and information security
management appropriate for the time-stamping services it is providing.
e) The TSA has adequate arrangements to cover liabilities arising from
its operations and/or activities.
f) It has the financial stability and resources required to operate in
conformity with this policy.
NOTE 1: This includes requirements for TSA termination identified in
section 7.4.9.
g) It employs a sufficient number of personnel having the necessary
education, training, technical knowledge and experience relating to the
type, range and volume of work necessary to provide time-stamping
services.
NOTE 2: Personnel employed by a TSA include individual personnel
contractually engaged in performing functions in support of the TSA's
time-stamping services. Personnel who may be involved only in
monitoring the TSA services need not be TSA personnel.
h) It has policies and procedures for the resolution of complaints and
disputes received from customers or other parties about the
provisioning of the time-stamping services or any other related
matters.
i) It has a properly documented agreement and contractual relationship
in place where the provisioning of services involves subcontracting,
outsourcing or other third party arrangements.
8. Security Considerations
When verifying time-stamp tokens it is necessary for the verifier to
ensure that the TSU certificate is trusted and not revoked. This means
that the security is dependent upon the security of the CA that has
issued the TSU certificate for both issuing the certificate and
providing accurate revocation status information for that certificate.
When a time-stamp is verified as valid at a given point of time, this
does not mean that it will necessarily remain valid later on. Every
time, a time-stamp token is verified during the validity period of
the TSU certificate, it must be verified again against the current
revocation status information, since in case of compromise of a TSU
private key, all the time-stamp tokens generated by that TSU become
invalid. Annex C provides guidance about the long term verification
of time-stamp tokens.
In applying time-stamping to applications, consideration also needs
to be given to the security of the application. In particular, when
applying time-stamps it is necessary to ensure that the integrity of
data is maintained before the time-stamp is applied. The requester
ought to really make sure that the hash value included in the
time-stamp token matches with the hash of the data.
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9. Acknowledgments
The development of this document was supported by ETSI and the
European Commission. Special thanks are due to Franco Ruggieri
for his valuable inputs.
10. References
10.1. Normative References
[RFC 2119] Bradner, S. "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[TF.460-5] ITU-R Recommendation TF.460-5 (1997):
Standard-frequency and time-signal emissions.
[TF.536-1] ITU-R Recommendation TF.536-1 (1998):
Time-scale notations.
[CWA 14167-2] CEN Workshop Agreement 14167-2: Cryptographic Module
for CSP Signing Operations - Protection Profile
(MCSO-PP).
[FIPS 140-1] FIPS PUB 140-1 (1994): Security Requirements for
Cryptographic Modules.
[ISO 15408] ISO/IEC 15408 (1999) (parts 1 to 3):
Information technology - Security techniques and
Evaluation criteria for IT security.
10.2. Non-normative References
[CWA 14172] CEN Workshop Agreement 14172: EESSI Conformity
Assessment Guidance.
[Dir 95/46/EC] Directive 95/46/EC of the European Parliament and
of the Council of 24 October 1995 on the protection
of individuals with regard to the processing of
personal data and on the free movement of such data.
[Dir 99/93/EC] Directive 1999/93/EC of the European Parliament and
of the Council of 13 December 1999 on a Community
framework for electronic signatures.
[ISO 17799] ISO/IEC 17799: Information technology
Code of practice for information security management
[RFC 3126] D. Pinkas, J. Ross, N. Pope. "Electronic Signature
Formats for long term electronic signatures".
RFC 3126. September 2001.
[RFC 3161] Adams, C., Cain, P., Pinkas, D. and R. Zuccherato,
"Internet X.509 Public Key Infrastructure Time-Stamp
Protocol (TSP)", RFC 3161, August 2001.
Pinkas, Pope, Ross Informational [Page 30]
Policy Requirements for Time-Stamping Authorities August 2003
[TS 101733] ETSI Technical Standard TS 101 733 V.1.2.2 (2000-12)
Electronic Signature Formats. Note: copies of ETSI
TS 101 733 can be freely downloaded from the ETSI web
site www.etsi.org.
[TS 101861] ETSI Technical Standard TS 101 861 V1.2.1. (2001-11).
Time stamping profile. Note: copies of ETSI TS 101 861
can be freely downloaded from the ETSI web site
www.etsi.org.
[TS 102023] ETSI Technical Standard TS 102 023.
Policy requirements for Time-Stamping Authorities.
Note: copies of ETSI TS 102 023 can be freely
downloaded from the ETSI web site www.etsi.org.
[X.208] CCITT Recommendation X.208: Specification of Abstract
Syntax Notation One (ASN.1), 1988.
11. Authors' addresses
Denis Pinkas
Bull
Rue Jean Jaures,
78340 Les Clayes CEDEX
FRANCE
EMail: Denis.Pinkas@bull.net
Nick Pope
Security & Standards
192 Moulsham Street
Chelmsford, Essex
CM2 0LG
United Kingdom
EMail: pope@secstan.com
John Ross
Security & Standards
192 Moulsham Street
Chelmsford, Essex
CM2 0LG
United Kingdom
EMail: ross@secstan.com
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Policy Requirements for Time-Stamping Authorities August 2003
This Informational RFC has been produced in ETSI ESI.
ETSI
F-06921 Sophia Antipolis, Cedex - FRANCE
650 Route des Lucioles - Sophia Antipolis
Valbonne - France
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Policy Requirements for Time-Stamping Authorities August 2003
Annex A (informative): Coordinated Universal Time
Coordinated Universal Time (UTC) is the international time standard
that became effective on January 1, 1972. UTC has superseded Greenwich
Mean Time (GMT), but in practice they are never more than 1 second
different. Hence many people continue to refer to GMT when in fact they
operate to UTC.
Zero (0) hours UTC is midnight in Greenwich, England, which lies on the
zero longitudinal meridian. Universal time is based on a 24 hour clock,
therefore, afternoon hours such as 4 pm UTC are expressed as 16:00 UTC
(sixteen hours, zero minutes).
International Atomic Time (TAI) is calculated by the Bureau
International des Poids et Mesures (BIPM) from the readings of more
than 200 atomic clocks located in metrology institutes and
observatories in more than 30 countries around the world. Information
on TAI is made available every month in the BIPM Circular T
(ftp://62.161.69.5/pub/tai/publication). It is that TAI does not lose
or gain with respect to an imaginary perfect clock by more than about
one tenth of a microsecond (0.0000001 second) per year.
Coordinated Universal Time (UTC): Time scale, based on the second, as
defined and recommended by the International Telecommunications Radio
Committee (ITU-R), and maintained by the Bureau International des Poids
et Mesures (BIPM). The maintenance by BIPM includes cooperation among
various national laboratories around the world. The full definition of
UTC is contained in ITU-R Recommendation TF.460-4.
Atomic Time, with the unit of duration the Systeme International (SI)
second defined as the duration of 9 192 631 770 cycles of radiation,
corresponds to the transition between two hyperfine levels of the
ground state of caesium 133. TAI is the International Atomic Time
scale, a statistical timescale based on a large number of atomic
clocks.
Universal Time (UT) is counted from 0 hours at midnight, with unit of
duration the mean solar day, defined to be as uniform as possible
despite variations in the rotation of the Earth.
- UT0 is the rotational time of a particular place of observation.
It is observed as the diurnal motion of stars or extraterrestrial
radio sources.
- UT1 is computed by correcting UT0 for the effect of polar motion
on the longitude of the observing site. It varies from uniformity
because of the irregularities in the Earth's rotation.
UT1, is based on the somewhat irregular rotation of the Earth.
Rotational irregularities usually result in a net decrease in the
Earth's average rotational velocity, and ensuing lags of UT1 with
respect to UTC.
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Coordinated Universal Time (UTC) is the basis for international
time-keeping and follows TAI exactly except for an integral number of
seconds, 32 in year 2001. These leap seconds are inserted on the advice
of the International Earth Rotation Service (IERS)
(http://hpiers.obspm.fr/) to ensure that, having taken into account
irregularities, the Sun is overhead within 0,9 seconds of 12:00:00 UTC
on the meridian of Greenwich. UTC is thus the modern successor of
Greenwich Mean Time, GMT, which was used when the unit of time was the
mean solar day.
Adjustments to the atomic, i.e., UTC, time scale consist of an
occasional addition or deletion of one full second, which is called a
leap second. Twice yearly, during the last minute of the day of June 30
and December 31, Universal Time, adjustments may be made to ensure that
the accumulated difference between UTC and UT1 will not exceed 0,9 s
before the next scheduled adjustment. Historically, adjustments, when
necessary, have usually consisted of adding an extra second to the UTC
time scale in order to allow the rotation of the Earth to "catch up."
Therefore, the last minute of the UTC time scale, on the day when an
adjustment is made, will have 61 seconds. Adjustments dates are
typically announced several months in advance in IERS Bulletin C:
ftp://hpiers.obspm.fr/iers/bul/bulc/bulletinc.dat.
Coordinated Universal Time (UTC) differs thus from TAI by an integral
number of seconds. UTC is kept within 0,9 s of UT1 by the introduction
of one-second steps to UTC, the "leap second." To date these steps have
always been positive.
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Policy Requirements for Time-Stamping Authorities August 2003
Annex B (informative): Possible for Implementation Architectures and
Time-stamping Services
B.1 Managed Time-stamping Service
Some organizations may be willing to host one or more Time-Stamping
Units in order to take advantage of both the proximity and the quality
of the Time-Stamping Service, without being responsible for the
installation, operation and management of these Time-Stamping
Units.
This can be achieved by using units that are installed in the premises
from the hosting organization and then remotely managed by a
Time-Stamping Authority that takes the overall responsibility of the
quality of the service delivered to the hosting organization.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ +
+ Time-Stamping Authority +
+ +
+ +
+_____________ _____________ _____________+
|+ __________ | | | | __________ +|
|+| | | | Time - | | | |+|
|+| Time - |<-------------| Stamping |------------->| Time - |+|
|+| Stamping | | Install. | Management | Install. | | Stamping |+|
|+| Unit | | Management | | Management | | Unit |+|
|+|__________| | |_____________| | |__________|+|
|+ | | +|
|+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++|
| Hosting | | Hosting |
| Organization | | Organization |
|______________| |______________|
Figure B.1: Managed Time-stamping Service
The requirements for time-stamping services described in the current
document includes requirements on both the time-stamping management and
for the operation of the unit which issues the time-stamp tokens. The
TSA, as identified in the time-stamp token, has the responsibility to
ensure that these requirements are met (for example through contractual
obligations).
It should be clear that the hosting organization will generally want to
be able to monitor the use of the service and, at a minimum, know
whether the service is working or not and even be able to measure the
performances of the service, e.g. the number of time-stamps generated
during some period of time. Such monitoring can be considered to be
outside of TSA's time-stamping authority.
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Policy Requirements for Time-Stamping Authorities August 2003
Therefore the description of the management operation described in the
main body of the document is not limitative. Monitoring operations, if
performed directly on the unit, may be permitted by the Time-Stamping
service provider.
B.2 Selective Alternative Quality
Some relying parties may be willing to take advantage of particular
characteristics from a time-stamp token such as a specific signature
algorithm and/or key length or a specific accuracy for the time
contained in the time stamp token. These parameters can be considered
as specifying a "quality" for the time stamp token.
Time stamp tokens with various qualities may be issued by different
time-stamping units operated by the same or different TSAs.
A particular time-stamping unit will only provide one combination of
algorithm and key length (since a time-stamping unit is a set of
hardware and software which is managed as a unit and has a single
time-stamp token signing key). In order to obtain different
combinations of algorithm and key length, different time-stamping
units shall be used.
A particular time-stamping unit may provide a fixed accuracy for the
time contained in the time stamp token or different accuracy if
instructed to do so either by using a specific mode of access (e.g.
e-mail or http) or by using specific parameters in the request.
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Policy Requirements for Time-Stamping Authorities August 2003
Annex C (informative): Long Term Verification of time-stamp tokens
Usually, a time-stamp token becomes unverifiable beyond the end of the
validity period of the certificate from the TSU, because the CA that
has issued the certificate does not warrant any more that it will
publish revocation data, including data about revocations due to key
compromises. However, verification of a time-stamp token might still be
performed beyond the end of the validity period of the certificate from
the TSU, if, at the time of verification, it can be known that:
- the TSU private key has not been compromised at any time up to the
time that a relying part verifies a time-stamp token;
- the hash algorithms used in the time-stamp token exhibits no
collisions at the time of verification;
- the signature algorithm and signature key size under which the
time-stamp token has been signed is still beyond the reach of
cryptographic attacks at the time of verification.
If these conditions cannot be met, then the validity may be maintained
by applying an additional time-stamp to protect the integrity of the
previous one.
The present document does not specify the details of how such
protection may be obtained. For the time being, and until some
enhancements are defined to support these features, the information may
be obtained using-out-of bands means or alternatively in the context of
closed environments. As an example, should a CA guaranty to maintain
the revocation status of TSU certificates after the end of its validity
period, this would fulfil the first requirement.
NOTE 1: An alternative to Time-Stamping is for a Trusted Service
Provider to record a representation of a datum bound to a particular
time in an audit trail, thus establishing evidence that the datum
existed before that time. This technique, which is called Time-Marking,
can be a valuable alternative for checking the long term validity of
signatures.
NOTE 2: The TSA or other trusted third party service provider may
support the verification of time-stamp tokens.
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Annex D (informative): Model TSA disclosure statement structure.
The TSA disclosure statement contains a section for each defined
statement type. Each section of a TSA disclosure statement contains a
descriptive statement, which MAY include hyperlinks to the relevant
certificate policy/certification practice statement sections.
D.1. STATEMENT TYPE: Entire agreement
STATEMENT DESCRIPTION: A statement indicating that the disclosure
statement is not the entire agreement, but only a part of it.
D.2. STATEMENT TYPE: TSA contact info
STATEMENT DESCRIPTION: The name, location and relevant contact
information for the TSA.
D.3. STATEMENT TYPE: time-stamp token types and usage
STATEMENT DESCRIPTION: A description of each class/type of
time-stamp tokens issued by the TSA (in accordance with each
time-stamp policy) and any restrictions on time-stamp usage.
SPECIFIC REQUIREMENT: Indication of the policy being applied,
including the contexts for which the time-stamp token can be used
(e.g. only for use with electronic signatures), the hashing
algorithms, the expected life time of the time-stamp token
signature, any limitations on the use of the time-stamp token and
information on how to verify the time-stamp token.
D.4. STATEMENT TYPE: Reliance limits.
STATEMENT DESCRIPTION: reliance limits, if any.
SPECIFIC REQUIREMENT: Indication of the accuracy of the time in
the time-stamp token, and the period of time for which TSA event
logs (see section 7.4.10) are maintained (and hence are available
to provide supporting evidence).
D.5. STATEMENT TYPE: Obligations of subscribers.
STATEMENT DESCRIPTION: The description of, or reference to, the
critical subscriber obligations.
SPECIFIC REQUIREMENT: No specific requirements identified in the
current document. Where applicable the TSA may specify additional
obligations.
D.6. STATEMENT TYPE: TSU public key status checking obligations of
relying parties.
STATEMENT DESCRIPTION: The extent to which relying parties are
obligated to check the TSU public key status, and references to
further explanation.
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SPECIFIC REQUIREMENT: Information on how to validate the TSU
public key status, including requirements to check the revocation
status of TSU public key, such that the relying party is
considered to "reasonably rely" on the time-stamp token (see
section 6.3).
D.7. STATEMENT TYPE: Limited warranty and disclaimer/Limitation of
liability.
STATEMENT DESCRIPTION: Summary of the warranty, disclaimers,
limitations of liability and any applicable warranty or insurance
programs
SPECIFIC REQUIREMENT: Limitations of liability (see section 6.4).
D.8. STATEMENT TYPE: Applicable agreements and practice statement.
STATEMENT DESCRIPTION: Identification and references to applicable
agreements, practice statement, time-stamp policy and other
relevant documents.
D.9. STATEMENT TYPE: Privacy policy.
STATEMENT DESCRIPTION: A description of and reference to the
applicable privacy policy.
SPECIFIC REQUIREMENT: Note: TSA's under this policy are required
to comply with the requirements of Data Protection Legislation.
D.10. STATEMENT TYPE: Refund policy
STATEMENT DESCRIPTION: A description of and reference to the
applicable refund policy.
D.11. STATEMENT TYPE: Applicable law, complaints and dispute resolution
mechanisms.
STATEMENT DESCRIPTION: Statement of the choice of law, complaints
procedure and dispute resolution mechanisms.
SPECIFIC REQUIREMENT: The procedures for complaints and dispute
settlements. The applicable legal system.
D.12. STATEMENT TYPE: TSA and repository licenses, trust marks, and
audit.
STATEMENT DESCRIPTION: Summary of any governmental licenses, seal
programs; and a description of the audit process and if
applicable the audit firm.
SPECIFIC REQUIREMENT: If the TSA has been assessed to be
conformant with the identified time-stamp policy, and if so
through which independent party.
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Pinkas, Pope, Ross Informational [Page 40]
