Internet Draft C. Adams (Entrust Technologies)
PKIX Working Group P. Cain (BBN)
expires in six months D. Pinkas (Bull)
R. Zuccherato (Entrust Technologies)
January 2001
Internet X.509 Public Key Infrastructure
Time Stamp Protocol (TSP)
<draft-ietf-pkix-time-stamp-13.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026.
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Copyright (C) The Internet Society (1999). All Rights Reserved.
Abstract
A time stamping service supports assertions of proof that a datum
existed before a particular time. This document describes the format
of a request sent to a Time Stamping Authority (TSA) and of the
response that is returned. It also establishes several security-
relevant requirements for TSA operation, with regards to processing
requests to generate responses. A TSA may be operated as a Trusted
Third Party (TTP) service, though other operational models may be
appropriate, e.g. an organization might require a TSA for internal
time stamping purposes.
Non-repudiation services [ISONR] require the ability to establish the
existence of data before specified times. This protocol may be used as
a building block to support such services. An example of how to prove
that a digital signature was generated during the validity period of
a public key certificate is given in an annex.
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
"SHALL", "RECOMMENDED", "MAY", and "OPTIONAL" in this document (in
uppercase, as shown) are to be interpreted as described in [RFC2119].
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1. Introduction
In order to associate a datum with a particular point in time, a
Time Stamp Authority (TSA) may need to be used. This Trusted Third
Party provides a "proof-of-existence" for this particular datum at an
instant in time.
The TSA's role is to time stamp a datum to establish evidence
indicating the time at which the datum existed. This can then be
used, for example, to verify that a digital signature was applied to
a message before the corresponding certificate was revoked thus
allowing a revoked public key certificate to be used for verifying
signatures created prior to the time of revocation. This is an
important public key infrastructure operation. The TSA can also be
used to indicate the time of submission when a deadline is critical,
or to indicate the time of transaction for entries in a log. An
exhaustive list of possible uses of a TSA is beyond the scope of
this document.
This standard does not establish overall security requirements for
TSA operation, just like other PKIX standards do not establish such
requirements for CA operation. Rather, it is anticipated that a TSA
will make known to prospective clients the policies it implements to
ensure accurate time stamp generation, and clients will make use of
the services of a TSA only if they are satisfied that these policies
meet their needs.
2. The TSA
The TSA is a TTP that creates time stamp tokens in order to indicate
that a datum existed at a particular point in time.
For the remainder of this document a "valid request" shall mean one
that can be decoded correctly, is of the form specified in Section 2.4,
and is from a supported TSA subscriber.
2.1. Requirements of the TSA
The TSA is REQUIRED:
1. to use a trustworthy source of time.
2. to include a trustworthy time value for each time stamp token.
3. to include a unique integer for each newly generated time
stamp token.
4. to produce a time stamp token upon receiving a valid request
from the requester, when it is possible.
5. to include within each time stamp token an identifier to
uniquely indicate the security policy under which the token
was created.
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6. to only time stamp a hash representation of the datum, i.e.
a data imprint associated with a one-way collision resistant
hash-function uniquely identified by an OID.
7. to examine the OID of the one-way collision resistant hash-
function and to verify that the hash value length is
consistent with the hash algorithm.
8. not to examine the imprint being time stamped in any way
(other than to check its length, as specified in the previous
bullet).
9. not to include any identification of the requesting entity in
the time stamp tokens.
10. to sign each time stamp token using a key generated
exclusively for this purpose and have this property of the
key indicated on the corresponding certificate.
11. to include additional information in the time stamp token,
if asked by the requester using the extensions field, only
for the extensions that are supported by the TSA. If this is
not possible, the TSA SHALL respond with an error message.
2.2. TSA Transactions
As the first message of this mechanism, the requesting entity requests
a time stamp token by sending a request (which is or includes a
TimeStampReq, as defined below) to the Time Stamping Authority. As
the second message, the Time Stamping Authority responds by sending a
response (which is or includes a TimeStampResp, as defined below) to
the requesting entity.
Upon receiving the response (which is or includes a TimeStampResp,
as defined below), the requesting entity SHALL verify the status error
returned in the response and if no error is present it SHALL verify the
various fields contained in the TimeStampToken and the validity of the
digital signature of the TimeStampToken. In particular, it SHALL verify
that what was time stamped corresponds to what was requested to be
time stamped. The requester SHALL verify that the TimeStampToken
contains the correct certificate identifier of the TSA, the correct
data imprint and the correct hash algorithm OID. It SHALL then verify
the timeliness of the response by verifying either the time included
in the response against a local trusted time reference, if one is
available, or the value of the nonce (large random number with a
high probability that it is generated by the client only once)
included in the response against the value included in the request.
For more details about replay attack detection, see the security
considerations section (item 6). If any of the verifications above
fails, the TimeStampToken SHALL be rejected.
Then, since the TSA's certificate may have been revoked, the status of
the certificate SHOULD be checked (e.g. by checking the appropriate
CRL) to verify that the certificate is still valid.
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Then, the client application SHOULD check the policy field to determine
whether or not the policy under which the token was issued is
acceptable for the application.
2.3. Identification of the TSA
The TSA MUST sign each time stamp message with a key reserved
specifically for that purpose. A TSA MAY have distinct private keys,
e.g. to accommodate different policies, different algorithms,
different private key sizes or to increase the performance. The
corresponding certificate MUST contain only one instance of the
extended key usage field extension as defined in [RFC2459]
Section 4.2.1.13 with KeyPurposeID having value:
id-kp-timeStamping. This extension MUST be critical.
The following object identifier identifies the KeyPurposeID
having value id-kp-timeStamping.
id-kp-timeStamping OBJECT IDENTIFIER ::= {iso(1)
identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7)
kp (3) timestamping (8)}
2.4. Request and Response Formats
2.4.1. Request Format
A time stamping request is as follows:
TimeStampReq ::= SEQUENCE {
version INTEGER { v1(1) },
messageImprint MessageImprint,
--a hash algorithm OID and the hash value of the data to be
--time stamped
reqPolicy TSAPolicyId OPTIONAL,
nonce INTEGER OPTIONAL,
certReq BOOLEAN DEFAULT FALSE,
extensions [0] IMPLICIT Extensions OPTIONAL
}
The version field (currently v1) describes the version of the
TimeStamp request.
The messageImprint field SHOULD contain the hash of the datum to be
time stamped. The hash is represented as an OCTET STRING. Its length
MUST match the length of the hash value for that algorithm (e.g.
20 bytes for SHA-1 or 16 bytes for MD5).
MessageImprint ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashedMessage OCTET STRING }
The hash algorithm indicated in the hashAlgorithm field SHOULD be a
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known hash algorithm (one-way and collision resistant). That means
that it SHOULD be one-way and collision resistant. The Time Stamp
Authority SHOULD check whether or not the given hash algorithm is
known to be "sufficient" (based on the current state of knowledge in
cryptanalysis and the current state of the art in computational
resources, for example). If the TSA does not recognize the hash
algorithm or knows that the hash algorithm is weak (a decision left to
the discretion of each individual TSA), then the TSA SHOULD refuse to
provide the Time Stamp Token by returning a pkiStatusInfo of 'bad_alg'.
The reqPolicy field, if included, indicates the TSA policy under which
the TimeStampToken SHOULD be provided. TSAPolicyId is defined as
follows:
TSAPolicyId ::= OBJECT IDENTIFIER
The nonce, if included, allows to verify the timeliness of the
response when no local clock is available. The nonce is a large random
number with a high probability that the client generates it only once
(e.g. a 64 bit integer). In such a case the same nonce value MUST be
included in the response, otherwise the response shall be rejected.
If the certReq field is present and set to true, the TSA's public
key certificate that is referenced by the ESSCertID attribute in the
response MUST be provided by the TSA in the certificates field from
the SignedData structure in that response. That field may also contain
other certificates.
If the certReq field is missing or if the certReq field is present
and set to false then the certificates field from the SignedData
structure MUST not be present in the response.
The extensions field is a generic way to add additional information to
the request in the future. Extensions is defined in [RFC 2459]. If an
extension, whether it is marked critical or not critical, is used
by a requester but is not recognized by a time stamping server, the
server SHALL not issue a token and SHALL return a failure
(unacceptedExtension).
The time stamp request does not identify the requester, as this
information is not validated by the TSA (See Section 2.1). In
situations where the TSA requires the identity of the requesting
entity, alternate identification /authentication means have to be used
(e.g. CMS encapsulation [CMS] or TLS authentication [RFC2246]).
2.4.2. Response Format
A time stamping response is as follows:
TimeStampResp ::= SEQUENCE {
status PKIStatusInfo,
timeStampToken TimeStampToken OPTIONAL
}
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The status is based on the definition of status in section 3.2.3
of [RFC2510] as follows:
PKIStatusInfo ::= SEQUENCE {
status PKIStatus,
statusString PKIFreeText OPTIONAL,
failInfo PKIFailureInfo OPTIONAL
}
When the status contains the value zero or one, a Time Stamp Token
MUST be present. When status contains a value other than zero or one,
a Time Stamp Token MUST NOT be present. One of the following values
MUST be contained in status:
PKIStatus ::= INTEGER {
granted (0),
-- when the PKIStatus contains the value zero a Time Stamp
Token, as requested, is present.
grantedWithMods (1),
-- when the PKIStatus contains the value one a Time Stamp
Token, with modifications, is present.
rejection (2),
waiting (3),
revocationWarning (4),
-- this message contains a warning that a revocation is
-- imminent
revocationNotification (5)
-- notification that a revocation has occurred
}
Compliant servers SHOULD NOT produce any other values.
Compliant clients MUST generate an error if values it does not
understand are present.
When the Time Stamp Token is not present, the failInfo indicates
the reason why the time stamp request was rejected and may be one of
the following values.
PKIFailureInfo ::= BIT STRING {
badAlg (0),
-- unrecognized or unsupported Algorithm Identifier
badRequest (2),
-- transaction not permitted or supported
badDataFormat (5),
-- the data submitted has the wrong format
timeNotAvailable (14),
-- the TSA's time source is not available
unacceptedPolicy (15),
-- the requested TSA policy is not supported by the TSA
unacceptedExtension (16),
-- the requested extension is not supported by the TSA
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addInfoNotAvailable (17)
-- the additional information requested could not be understood
-- or is not available
systemFailure (25)
-- the request cannot be handled due to system failure
}
These are the only values of PKIFailureInfo that SHALL be supported.
Compliant servers SHOULD NOT produce any other values.
Compliant clients MUST generate an error if values it does not
understand are present.
The statusString field of PKIStatusInfo MAY be used to include reason
text such as "messageImprint field is not correctly formatted".
A TimeStampToken is as follows. It is defined as a ContentInfo ([CMS])
and SHALL encapsulate a signed data content type.
TimeStampToken ::= ContentInfo
-- contentType is id-signedData ([CMS])
-- content is SignedData ([CMS])
The fields of type EncapsulatedContentInfo of the SignedData construct
have the following meanings:
eContentType is an object identifier that uniquely specifies the
content type. For a time stamping token it is defined as:
id-ct-TSTInfo OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) ct(1) 4}
eContent is the content itself, carried as an octet string.
The eContent SHALL be the DER-encoded value of TSTInfo.
The time stamp token MUST NOT contain any signatures other than the
signature of the TSA. The certificate identifier (ESSCertID) of the
TSA certificate MUST be included as a signerInfo attribute.
TSTInfo ::= SEQUENCE {
version INTEGER { v1(1) },
policy TSAPolicyId,
messageImprint MessageImprint,
-- MUST have the same value as the similar field in
-- TimeStampReq
serialNumber INTEGER,
-- Time Stamps users MUST be ready to accommodate integers
-- up to 160 bits.
genTime GeneralizedTime,
accuracy Accuracy OPTIONAL,
ordering BOOLEAN DEFAULT FALSE,
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nonce INTEGER OPTIONAL,
-- MUST be present if the similar field was present
-- in TimeStampReq. In that case it MUST have the same value.
tsa [0] GeneralName OPTIONAL,
extensions [1] IMPLICIT Extensions OPTIONAL
}
The version field (currently v1) describes the version of the
Timestamp token.
Conforming timestamping servers MUST be able to provide version 1
Timestamp tokens.
Among the optional fields, only the nonce field MUST be supported.
Conforming timestamping requesters MUST be able to recognize version 1
Timestamp tokens with all the optional fields present, but are not
mandated to understand the semantics of any extension, if present.
The policy field MUST indicate the TSA's policy under which the
response was produced. If a similar field was present in the
TimeStampReq, then it MUST have the same value, otherwise an error
(unacceptedPolicy) MUST be returned. This policy MAY include the
following types of information (although this list is certainly not
exhaustive):
* The conditions under which the time stamp may be used.
* The availability of a time-stamp log, to allow later verification
that a time-stamp token is authentic.
The messageImprint MUST have the same value as the similar field in
TimeStampReq, provided that the size of the hash value matches the
expected size of the hash algorithm identified in hashAlgorithm.
The serialNumber field is an integer assigned by the TSA to each
TimeStampToken. It MUST be unique for each TimeStampToken issued by
a given TSA (i.e., the TSA name and serial number identify a unique
TimeStampToken). It should be noticed that the property MUST be
preserved even after a possible interruption (e.g. crash) of the
service.
genTime is the time at which the timestamp has been created by the
TSA. The ASN.1 GeneralizedTime syntax can include fraction-of-second
details. Such syntax, without the restrictions from [RFC 2459]
Section 4.1.2.5.2, where GeneralizedTime is limited to represent the
time with a granularity of one second, may be used here.
GeneralizedTime values MUST include seconds. However, when there is no
need to have a precision better than the second, then GeneralizedTime
with a precision limited to one second SHOULD be used (as in [RFC 2459]).
The syntax is: YYYYMMDDhhmmss[.s...]Z
Example: 19990609001326.34352Z
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X.690 | ISO/IEC 8825-1 provides the restrictions for a DER-encoding.
The encoding MUST terminate with a "Z". The decimal point element,
if present, MUST be the point option ".". The fractional-seconds
elements, if present, MUST omit all trailing 0's; if the elements
correspond to 0, they MUST be wholly omitted, and the decimal point
element also MUST be omitted.
Midnight (GMT) shall be represented in the form: "YYYYMMDD000000Z"
where "YYYYMMDD" represents the day following the midnight in question.
Here are a few examples of valid representations:
"19920521000000Z"
"19920622123421Z"
"19920722132100.3Z"
accuracy represents the time deviation around the UTC time contained in
GeneralizedTime.
Accuracy ::= SEQUENCE {
seconds INTEGER OPTIONAL,
millis [0] INTEGER (1..999) OPTIONAL,
micros [1] INTEGER (1..999) OPTIONAL
}
If either seconds, millis or micros is missing, then a value of zero
MUST be taken for the missing field.
By adding the accuracy value to the GeneralizedTime, an upper limit
of the time at which the timestamp has been created by the TSA can
be obtained. In the same way, by subtracting the accuracy to the
GeneralizedTime, a lower limit of the time at which the timestamp
has been created by the TSA can be obtained.
accuracy can be decomposed in seconds, milliseconds (between 1-999)
and microseconds (1-999), all expressed as integer.
When the accuracy optional field is not present, then the accuracy
may be available through other means, e.g. the TSAPolicyId.
If the ordering field is missing, or if the ordering field is present
and set to false, then the genTime field only indicates the time at
which the timestamp has been created by the TSA. In such a case, the
ordering of Time Stamps tokens issued by the same TSA or different
TSAs is only possible when the difference between the genTime of the
first Time Stamp token and the genTime of the second Time Stamp token
is greater than the sum of the accuracies of the genTime for each Time
Stamp token.
If the ordering field is present and set to true, every Time Stamp
token from the same TSA can always be ordered based on the genTime
field, regardless of the genTime accuracy.
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The nonce field MUST be present if it was present in the TimeStampReq.
In such a case it MUST equal the value provided in the TimeStampReq
structure.
The purpose of the tsa field is to give a hint in identifying the
name of the TSA. If present, it MUST correspond to one of the subject
names included in the certificate that is to be used to verify the
token. However, the actual identification of the entity that signed
the response will always occur through the use of the certificate
identifier (ESSCertID Attribute) which is part of the signerInfo
(See Section 5 of [ESS]).
extensions is a generic way to add additional information in the
future. Extensions is defined in [RFC 2459].
Particular extension field types may be specified in standards or
may be defined and registered by any organization or community.
3. Transports
There is no mandatory transport mechanism for TSA messages in this
document. The mechanisms described below are optional; additional
optional mechanisms may be defined in the future.
3.1. Time Stamp Protocol Using E-mail
This section specifies a means for conveying ASN.1-encoded messages
for the protocol exchanges described in Section 2 and Appendix D via
Internet mail.
Two MIME objects are specified as follows:
Content-Type: application/timestamp-query
Content-Transfer-Encoding: base64
<<the ASN.1 DER-encoded Time Stamp message, base64-encoded>>
Content-Type: application/timestamp-reply
Content-Transfer-Encoding: base64
<<the ASN.1 DER-encoded Time Stamp message, base64-encoded>>
These MIME objects can be respectively sent and received using common
MIME processing engines and provides a simple Internet mail transport
for Time Stamp messages.
For the application/timestamp-query and application/timestamp-reply
MIME types, implementations SHOULD include the optional "name" and
"filename" parameters. Including a file name helps preserve type
information when timestamps are saved as files. When these parameters
are included, a file name with the appropriate extension SHOULD be
selected:
MIME Type File Extension
application/timestamp-query .TSQ
application/timestamp-reply .TSR
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In addition, the file name SHOULD be limited to eight characters
followed by a three letter extension. The eight character filename
base can be any distinct name.
3.2. File Based Protocol
A file containing a time stamp message MUST contain only the DER
encoding of one TSA message, i.e. there MUST be no extraneous header or
trailer information in the file. Such files can be used to transport
time stamp messages using for example, FTP.
A Time Stamp Request SHOULD be contained in a file with file extension
ô.tsqö (like Time Stamp Query). A Time Stamp Response SHOULD be
contained in a file with file extension ô.tsrö (like Time Stamp Reply).
3.3. Socket Based Protocol
The following simple TCP-based protocol is to be used for transport
of TSA messages. This protocol is suitable for cases where an
entity initiates a transaction and can poll to pick up the results.
The protocol basically assumes a listener process on a TSA that
can accept TSA messages on a well-defined port (IP port number 318).
Typically an initiator binds to this port and submits the initial
TSA message. The responder replies with a TSA message and/or with
a reference number to be used later when polling for the actual TSA
message response.
If a number of TSA response messages are to be produced for a given
request (say if a receipt must be sent before the actual token can be
produced) then a new polling reference is also returned.
When the final TSA response message has been picked up by the
initiator then no new polling reference is supplied.
The initiator of a transaction sends a "direct TCP-based TSA message"
to the recipient. The recipient responds with a similar message.
A "direct TCP-based TSA message" consists of:
length (32-bits), flag (8-bits), value (defined below)
The length field contains the number of octets of the remainder of
the message (i.e., number of octets of "value" plus one). All 32-bit
values in this protocol are specified to be in network byte order.
Message name flag value
tsaMsg '00'H DER-encoded TSA message
-- TSA message
pollRep '01'H polling reference (32 bits),
time-to-check-back (32 bits)
-- poll response where no TSA message response ready; use polling
-- reference value (and estimated time value) for later polling
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pollReq '02'H polling reference (32 bits)
-- request for a TSA message response to initial message
negPollRep '03'H '00'H
-- no further polling responses (i.e., transaction complete)
partialMsgRep '04'H next polling reference (32 bits),
time-to-check-back (32 bits),
DER-encoded TSA message
-- partial response (receipt) to initial message plus new polling
-- reference (and estimated time value) to use to get next part of
-- response
finalMsgRep '05'H DER-encoded TSA message
-- final (and possibly sole) response to initial message
errorMsgRep '06'H human readable error message
-- produced when an error is detected (e.g., a polling reference
-- is received which doesn't exist or is finished with)
The sequence of messages that can occur is:
a) entity sends tsaMsg and receives one of pollRep, negPollRep,
partialMsgRep or finalMsgRep in response.
b) end entity sends pollReq message and receives one of negPollRep,
partialMsgRep,finalMsgRep or errorMsgRep in response.
The "time-to-check-back" parameter is an unsigned 32-bit integer,
defined to be the number of seconds that have elapsed since midnight,
January 1, 1970, coordinated universal time.
It provides an estimate of the time that the end entity should send
its next pollReq.
3.4. Time Stamp Protocol via HTTP
This subsection specifies a means for conveying ASN.1-encoded messages
for the protocol exchanges described in Section 2 and Appendix D via the
HyperText Transfer Protocol.
Two MIME objects are specified as follows.
Content-Type: application/timestamp-query
<<the ASN.1 DER-encoded Time Stamp Request message>>
Content-Type: application/timestamp-reply
<<the ASN.1 DER-encoded Time Stamp Response message>>
These MIME objects can be sent and received using common HTTP
processing engines over WWW links and provides a simple browser-
server transport for Time Stamp messages.
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Upon receiving a valid request, the server MUST respond with either a
valid response with content type application/timestamp-response or
with an HTTP error.
4. Security Considerations
This entire document concerns security considerations.
When designing a TSA service, the following considerations have been
identified that have an impact upon the validity or "trust" in the time
stamp token.
1. When a TSA shall not be used anymore, but the TSA private key
has not been compromised, the authority's certificate SHALL
be revoked. When the reasonCode extension relative to the
revoked certificate from the TSA is present in the CRL entry
extensions, it SHALL be set either to unspecified (0),
affiliationChanged (3), superseded (4) or cessationOfOperation
(5). In that case, at any future time, the tokens signed with
the corresponding key will be considered as invalid, but
tokens generated before the revocation time will remain valid.
When the reasonCode extension relative to the revoked
certificate from the TSA is not present in the CRL entry
extensions, then all the tokens that have been signed with
the corresponding key SHALL be considered as invalid. For
that reason, it is recommended to use the reasonCode
extension.
2. When the TSA private key has been compromised, then the
corresponding certificate SHALL be revoked. In that case,
the reasonCode extension relative to the revoked certificate
from the TSA may or may not be present in the CRL entry
extensions. When it is present then it SHALL be set to
keyCompromise (1). Any token signed by the TSA using that
private key cannot be trusted anymore. For this reason, it
is imperative that the TSA's private key be guarded with
proper security and controls in order to minimize the
possibility of compromise. 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. A double time stamping from two
different TSAs is another way to address this issue.
3. The TSA signing key MUST be of a sufficient length to allow
for a sufficiently long lifetime. Even if this is done, the key
will have a finite lifetime. Thus, any token signed by the
TSA SHOULD be time stamped again (if authentic copies of old
CRLs are available) or notarized (if they aren't) at a later
date to renew the trust that exists in the TSA's signature.
Time stamp tokens could also be kept with an Evidence Recording
Authority to maintain this trust.
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4. A client application using application using only a nonce and
no local clock SHOULD be concerned about the amount of time it
is willing to wait for a response. A `man-in-the-middle'
attack can introduce delays. Thus, any TimeStampResp that
takes more than an acceptable period of time SHOULD be
considered suspect. Since each transport method specified in
this document has different delay characteristics, the period
of time that is considered acceptable will depend upon the
particular transport method used, as well as other environment
factors.
5. If different entities obtain timestamps on the same data object
using the same hash algorithm, or a single entity obtains
multiple timestamps on the same object, the generated timestamp
tokens will include identical message imprints; as a result, an
observer with access to those timestamp tokens could infer that
the timestamps may refer to the same underlying data.
6. Inadvertent or deliberate replays for requests incorporating
the same hash algorithm and value may happen. Inadvertent
replays occur when more than one copy of the same request
message gets sent to the TSA because of problems in the
intervening network elements. Deliberate replays occur when
a middleman is replaying legitimate TS responses. In order to
detect these situations, several techniques may be used. Using
a nonce always allows to detect replays, and hence its use is
RECOMMENDED. Another possibility is to use both a local clock
and a moving time window during which the requester remembers
all the hashes sent during that time window. When receiving a
response, the requester ensures both that the time of the
response is within the time window and that there is only one
occurrence of the hash value in that time window. If the same
hash value is present more than once within a time window,
the requester may either use a nonce, or wait until the time
window has moved to come back to the case where the same hash
value appears only once during that time window.
5. Intellectual Property Rights
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to per-
tain to the implementation or use of the technology described in this
document or the extent to which any license under such rights might
or might not be available; neither does it represent that it has made
any effort to identify any such rights. Information on the IETF's
procedures with respect to rights in standards-track and standards-
related documentation can be found in BCP-11. Copies of claims of
rights made available for publication and any assurances of licenses
to be made available, or the result of an attempt made to obtain a
general license or permission for the use of such proprietary rights
by implementors or users of this specification can be obtained from
the IETF Secretariat.
Adams, Cain, Pinkas, Zuccherato [ Page 14 ]
Time Stamp Protocol Document Expiration : July 2001
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
The following eight (8) United States Patents related to time
stamping, listed in chronological order, are known by the authors
to exist at this time. This may not be an exhaustive list. Other
patents MAY exist or be issued at any time.
Implementers of this protocol SHOULD perform their own patent search
and determine whether or not any encumbrances exist on their
implementation.
Users of this protocol SHOULD perform their own patent search
and determine whether or not any encumbrances exist on the use of
this standard.
# 5,001,752 Public/Key Date-Time Notary Facility
Filing date: October 13, 1989
Issued: March 19, 1991
Inventor: Addison M. Fischer
# 5,022,080 Electronic Notary
Filing date: April 16, 1989
Issued: June 4, 1991
Inventors: Robert T. Durst, Kevin D. Hunter
# 5,136,643 Public/Key Date-Time Notary Facility
Filing date: December 20, 1990
Issued: August 4, 1992
Inventor: Addison M. Fischer
Note: This is a continuation of patent # 5,001,752.)
# 5,136,646 Digital Document Time-Stamping with Catenate Certificate
Filing date: August 2, 1990
Issued: August 4, 1992
Inventors: Stuart A. Haber, Wakefield S. Stornetta Jr.
(assignee) Bell Communications Research, Inc.,
# 5,136,647 Method for Secure Time-Stamping of Digital Documents
Filing date: August 2, 1990
Issued: August 4, 1992
Inventors: Stuart A. Haber, Wakefield S. Stornetta Jr.
(assignee) Bell Communications Research, Inc.,
# 5,373,561 Method of Extending the Validity of a Cryptographic
Certificate
Filing date: December 21, 1992
Issued: December 13, 1994
Inventors: Stuart A. Haber, Wakefield S. Stornetta Jr.
(assignee) Bell Communications Research, Inc.,
Adams, Cain, Pinkas, Zuccherato [ Page 15 ]
Time Stamp Protocol Document Expiration : July 2001
# 5,422,953 Personal Date/Time Notary Device
Filing date: May 5, 1993
Issued: June 6, 1995
Inventor: Addison M. Fischer
# 5,781,629 Digital Document Authentication System
Filing date: February 21, 1997
Issued: July 14, 1998
Inventor: Stuart A. Haber, Wakefield S. Stornetta Jr.
(assignee) Surety Technologies, Inc.,
6. References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2246] T. Dierks, C. Allen, "The TLS Protocol, Version 1.0,"
RFC 2246, January 1999.
[RFC2510] C. Adams, S. Farrell, "Internet X.509 Public Key
Infrastructure, Certificate Management Protocols,"
RFC 2510,March 1999.
[RFC2459] R. Housley, W. Ford, W. Polk, D. Solo, "Internet X.509
Public Key Infrastructure, Certificate and CRL Profile,"
RFC 2459, January 1999.
[CMS] R. Housley, "Cryptographic Message Syntax", RFC 2630,
June 1999.
[DSS] Digital Signature Standard. FIPS Pub 186. National
Institute of Standards and Technology. 19 May 1994.
[ESS] P. Hoffman, "Enhanced Security Services for S/MIME",
RFC 2634, June 1999.
[ISONR] ISO/IEC 10181-5: Security Frameworks in Open Systems.
Non-Repudiation Framework. April 1997.
[MD5] "The MD5 Message-Digest Algorithm", RFC 1321, Rivest, R.,
April 1992.
[SHA1] Secure Hash Standard. FIPS Pub 180-1. National Institute
of Standards and Technology. 17 April 1995.
7. Authors' Addresses
Carlisle Adams Pat Cain
Entrust Technologies BBN
750 Heron Road 70 Fawcett Street
Ottawa, Ontario Cambridge, MA 02138
K1V 1A7 U.S.A.
CANADA pcain@bbn.com
cadams@entrust.com
Adams, Cain, Pinkas, Zuccherato [ Page 16 ]
Time Stamp Protocol Document Expiration : July 2001
Denis Pinkas Robert Zuccherato
Bull S.A. Entrust Technologies
68 route de Versailles 750 Heron Road
B.P. 434 Ottawa, Ontario
78430 Louveciennes K1V 1A7
FRANCE CANADA
Denis.Pinkas@bull.net robert.zuccherato@entrust.com
Adams, Cain, Pinkas, Zuccherato [ Page 17 ]
Time Stamp Protocol Document Expiration : July 2001
APPENDIX A - Signature Timestamp attribute using CMS
One of the major use of time stamping is to time stamp a digital
signature to prove that the digital signature was created before
a given time. Should the corresponding public key certificate be
revoked this allows to know whether the signature was created before
or after the revocation date.
A sensible place to store a time stamp is in a [CMS] structure
as an unsigned attribute.
This appendix defines a Signature Timestamp attribute that may be used
to timestamp a digital signature.
The following object identifier identifies the Signature Timestamp
attribute:
id-aa-timeStampToken OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) aa(2) 14 }
The Signature timestamp attribute value has ASN.1 type
SignatureTimeStampToken:
SignatureTimeStampToken ::= TimeStampToken
The value of messageImprint field within TimeStampToken shall be a hash
of the value of signature field within SignerInfo for the signedData
being timestamped.
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APPENDIX B - Placing a Signature At a Particular Point in Time
We present an example of a possible use of this general time stamping
service. It places a signature at a particular point in time, from
which the appropriate certificate status information (e.g. CRLs) MUST
be checked. This application is intended to be used in conjunction
with evidence generated using a digital signature mechanism.
Signatures can only be verified according to a non-repudiation policy.
This policy MAY be implicit or explicit (i.e., indicated in the
evidence provided by the signer). The non-repudiation policy can
specify, among other things, the time period allowed by a signer to
declare the compromise of a signature key used for the generation of
digital signatures. Thus a signature may not be guaranteed to be valid
until the termination of this time period.
To verify a digital signature, the following basic technique may be
used:
A) Time stamping information needs to be obtained soon after the
signature has been produced (e.g. within a few minutes or hours).
1) The signature is presented to the Time Stamping Authority (TSA).
The TSA then returns a TimeStampToken (TST) upon that signature.
2) The invoker of the service MUST then verify that the
TimeStampToken is correct.
B) The validity of the digital signature may then be verified in the
following way:
1) the Time stamp itself MUST be verified and it MUST be verified
that it applies to the signature of the signer.
2) The date/time indicated by the TSA in the Time Stamping Token
MUST be retrieved.
3) The certificate used by the signer MUST be identified
and retrieved.
4) The date/time indicated by the TSA MUST be inside the validity
period of the signer's certificate.
5) The revocation information about that certificate, at the
date/time of the Time Stamping operation, MUST be retrieved.
6) Should the certificate be revoked, then the date/time of
revocation shall be later than the date/time indicated by
the TSA
If all these conditions are successful, then the digital signature
shall be declared as valid.
Adams, Cain, Pinkas, Zuccherato [ Page 19 ]
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Appendix C: ASN.1 Module using 1988 Syntax
PKIXTSP {iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-tsp(13)}
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORTS ALL --
IMPORTS
Extensions, AlgorithmIdentifier
FROM PKIX1Explicit88 {iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7)
id-mod(0) id-pkix1-explicit-88(1)}
GeneralName FROM PKIX1Implicit88 {iso(1)
identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-pkix1-implicit-88(2)}
ContentInfo FROM CryptographicMessageSyntax {iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) cms(1)}
PKIFreeText FROM PKIXCMP {iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-cmp(9)} ;
-- Locally defined OIDs --
-- eContentType for a time stamping token
id-ct-TSTInfo OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) ct(1) 4}
-- 2.4.1
TimeStampReq ::= SEQUENCE {
version INTEGER { v1(1) },
messageImprint MessageImprint,
--a hash algorithm OID and the hash value of the data to be
--time stamped
reqPolicy TSAPolicyId OPTIONAL,
nonce INTEGER OPTIONAL,
certReq BOOLEAN DEFAULT FALSE,
extensions [0] IMPLICIT Extensions OPTIONAL
}
MessageImprint ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashedMessage OCTET STRING }
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Time Stamp Protocol Document Expiration : July 2001
TSAPolicyId ::= OBJECT IDENTIFIER
-- 2.4.2
TimeStampResp ::= SEQUENCE {
status PKIStatusInfo,
timeStampToken TimeStampToken OPTIONAL
}
-- The status is based on the definition of status
-- in section 3.2.3 of [RFC2510]
PKIStatusInfo ::= SEQUENCE {
status PKIStatus,
statusString PKIFreeText OPTIONAL,
failInfo PKIFailureInfo OPTIONAL
}
PKIStatus ::= INTEGER {
granted (0),
-- when the PKIStatus contains the value zero a Time Stamp
Token, as requested, is present.
grantedWithMods (1),
-- when the PKIStatus contains the value one a Time Stamp
Token, with modifications, is present.
rejection (2),
waiting (3),
revocationWarning (4),
-- this message contains a warning that a revocation is
-- imminent
revocationNotification (5)
-- notification that a revocation has occurred
}
-- When the Time Stamp Token is not present
-- failInfo indicates the reason why the
-- time stamp request was rejected and
-- may be one of the following values.
PKIFailureInfo ::= BIT STRING {
badAlg (0),
-- unrecognized or unsupported Algorithm Identifier
badRequest (2),
-- transaction not permitted or supported
badDataFormat (5),
-- the data submitted has the wrong format
timeNotAvailable (14),
-- the TSA's time source is not available
unacceptedPolicy (15),
-- the requested TSA policy is not supported by the TSA.
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Time Stamp Protocol Document Expiration : July 2001
unacceptedExtension (16),
-- the requested extension is not supported by the TSA.
addInfoNotAvailable (17)
-- the additional information requested could not be understood
-- or is not available
systemFailure (25)
-- the request cannot be handled due to system failure
}
TimeStampToken ::= ContentInfo
-- contentType is id-signedData as defined in [CMS]
-- content is SignedData as defined in([CMS])
-- eContentType within SignedData is id-ct-TSTInfo
-- eContent within SignedData is TSTInfo
TSTInfo ::= SEQUENCE {
version INTEGER { v1(1) },
policy TSAPolicyId,
messageImprint MessageImprint,
-- MUST have the same value as the similar field in
-- TimeStampReq
serialNumber INTEGER,
-- Time Stamps users MUST be ready to accommodate integers
-- up to 160 bits.
genTime GeneralizedTime,
accuracy Accuracy OPTIONAL,
ordering BOOLEAN DEFAULT FALSE,
nonce INTEGER OPTIONAL,
-- MUST be present if the similar field was present
-- in TimeStampReq. In that case it MUST have the same value.
tsa [0] GeneralName OPTIONAL,
extensions [1] IMPLICIT Extensions OPTIONAL
}
Accuracy ::= SEQUENCE {
seconds INTEGER OPTIONAL,
millis [0] INTEGER (1..999) OPTIONAL,
micros [1] INTEGER (1..999) OPTIONAL
}
END
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APPENDIX D - Full Copyright Statement
Copyright (C) The Internet Society 1999. All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of develop-
ing Internet standards in which case the procedures for copyrights
defined in the Internet Standards process shall be followed, or as
required to translate it into languages other than English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns. This
document and the information contained herein is provided on an "AS
IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL
NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY
OR FITNESS FOR A PARTICULAR PURPOSE.
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APPENDIX E: Access descriptors for timeStamping.
[This annex describes an extension based on the SIA extension that
will be defined in the "son-of-RFC2459". Since at the time of
publication of this document, "son-of-RFC2459" is not yet available,
its description is placed in an informative annex. This annex will
become normative, when this document will move from Proposed Standard
to Standard.]
A TSA's certificate MAY contain a Subject Information Access (SIA)
extension [son of RFC2459] in order to convey the method of contacting
the TSA. The accessMethod field in this extension MUST contain the
OID id-ad-timestamping:
The following object identifier identifies the access descriptors
for timeStamping.
id-ad-timeStamping OBJECT IDENTIFIER ::= {iso(1)
identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7)
ad (48) timestamping (3)}
The value of the accessLocation field defines the transport (e.g. HTTP)
used to access the TSA and may contain other transport dependent
information (e.g. a URL).
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Time Stamp Protocol Document Expiration : July 2001
APPENDIX F MIME Registrations
F.1 timestamp-query registration
To: ietf-types@iana.org
Subject: Registration of MIME media type application/timestamp-query
MIME media type name: application
MIME subtype name: timestamp-query
Required parameters: None
Optional parameters: None
Encoding considerations: Base64
Security considerations: Carries a request for a timestamp.
Interoperability considerations: None
Published specification: IETF PKIX Working Group Draft on Time Stamp
Protocols
Applications which use this media type: Time Stamp clients
Additional information:
Magic number(s): None
File extension(s): .TSQ
Macintosh File Type Code(s): none
Person & email address to contact for further information:
Denis Pinkas <denis.pinkas@bull.net>
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Time Stamp Protocol Document Expiration : July 2001
F.2 timestamp-reply registration
To: ietf-types@iana.org
Subject: Registration of MIME media type application/timestamp-reply
MIME media type name: application
MIME subtype name: timestamp-reply
Required parameters: None
Optional parameters: None
Encoding considerations: Base64
Security considerations: Carries a timestamp response. The response is
cryptographically signed.
Interoperability considerations: None
Published specification: IETF PKIX Working Group Draft on Time Stamp
Protocols
Applications which use this media type: Time Stamp clients
Additional information:
Magic number(s): None
File extension(s): .TSR
Macintosh File Type Code(s): none
Person & email address to contact for further information:
Denis Pinkas <denis.pinkas@bull.net>
Adams, Cain, Pinkas, Zuccherato [ Page 26 ]
Datatracker
Report a datatracker bug
draft-ietf-pkix-time-stamp-13
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