A. Santoni
Internet Draft Actalis S.p.A.
Intended status: Proposed Standard November 19, 2007
Expires: May 2008
Syntax for binding documents with time stamps
draft-santoni-timestampeddata-01.txt
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document describes a syntax which can be used to bind a generic
document (or any set of data, not necessarily protected by means of
cryptographic techniques) to one or more time-stamp tokens obtained
for that document, where "time-stamp token" has the meaning defined
in [TSP]. Additional types of temporal evidence are also supported.
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Whereas digital time stamping has become the standard technique for
proving the existence of a document before a certain point in time,
there is not a generally accepted syntax for keeping together one
document and the associated time-stamps in a single "bundle". Such a
syntax would facilitate keeping track of which time-stamps belong to
what documents and would therefore improve the efficiency of
timestamp-aware applications.
This document proposes a simple syntax based on [CMS], by defining a
new contentType.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [KWORDS].
Table of Contents
1. Introduction................................................2
2. Syntax for TimeStampedData...................................3
3. Compliance requirements......................................4
4. Recommanded processing.......................................5
5. Recommended file extentions..................................6
6. Security Considerations......................................6
7. IANA Considerations.........................................6
8. Acknowledgments.............................................6
9. References..................................................7
Author's Addresses.............................................7
Intellectual Property Statement.................................7
Disclaimer of Validity.........................................8
1. Introduction
Digital time stamping has become the standard technique for proving
the existence of a document before a certain point in time. Several
digital signature legislations around the world embrace the concept
and provide for time-stamping services as an approved means for
attesting the signing time and/or for extending the validity of
signed documents beyond the expiry date of the signers certificate.
However, while digital time stamping enhances digital signature, its
value does not depend on this latter. It can obviously be useful to
time-stamp a document even if this is not signed. And it can also be
useful, or even mandatory in some cases, to time-stamp a document in
its entirety, regardless of how many signatures it contains.
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When a time-stamp is related to a digital signature, there already
exist a way to keep the two pieces together: [TSP] describes how one
or more TimeStampTokens can be included in a SignerInfo structure as
unsigned attributes. On the other hand, when time-stamps are not
related to a digital signature, there is no standard way to keep
together the time-stamped document and the related time-stamps.
In such cases two approaches are typically being adopted:
o time-stamps are kept as separate files (keeping track of what
time-stamps belong to what documents is up to the user);
o an ad hoc solution is adopted for specific applications, like e.g.
a ZIP archive or a proprietary "envelope" of some kind.
Both solutions are obviously inadequate when interoperability is
aimed at, like in this memo.
This document proposes a simple syntax for bundling one document
(actually, any kind of file) to the corresponding temporal evidence,
this latter being typically represented by one or more RFC 3161
TimeStampTokens [TSP]. Additional types of temporal evidence, like
e.g. an RFC 4998 EvidenceRecord, are also supported via an "open"
syntax. However, for the sake of interoperability, the emphasis is
given to TimeStampTokens.
The proposed syntax is broadly based on the [CMS] syntax.
2. Syntax for TimeStampedData
The proposed data structure is called TimeStampedData. It is a new
variation of ContentInfo [CMS] marked by the following specific
contentType OID:
id-timestamped-data OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs7(7) 7 }
This particular OID signals that the content field of the ContentInfo
has the following syntax:
TimeStampedData ::= SEQUENCE {
version INTEGER { v1(1) },
fileName UTF8String,
mimeType PrintableString,
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content OCTET STRING,
evidence Evidence
}
Evidence ::= CHOICE {
timeStamps [0] SET (SIZE(1..MAX)) OF TimeStampToken
-- additional evidence types to be registered with the IETF
}
The version field contains the version number of the TimeStampedData
syntax. The initial version number is 1.
The fileName field contains the original filename (without path) of
the document which was time-stamped and whose content was inserted
into the TimeStampedData structure.
The mimeType field contains a MIME type (according to [MIME]) for the
bundled file. It is an advisory information which may help decide how
to open the file after having "detached" it from the TimeStampedData
structure, regardless of the filename extension (which could be
missing or unknown).
The content field carries the entire content, in its original format,
of the file which was time-stamped. The file need not be a document
in the strict sense; it can be any kind of file (e.g. an executable,
a database, etc).
The evidence field carries the evidence that the content data existed
before a certain point in time. Different types of evidence can be
used, in theory, but this document defines and mandates support for
one specific type: a non-empy set of RFC 3161 TimeStampToken's [TSP].
Additional types of evidence may be used after having registered them
(and having had a distinguishing tag assigned to them) with the IETF.
A suitable registration procedure will be defined for that purpose.
3. Compliance requirements
Compliant applications MUST support the RFC 3161-based type of
evidence (i.e. the timeStamps CHOICE).
Compliant applications SHALL always populate the fileName field of
TimeStampedData structure with a non-empty string, which is supposed
to be the real name of the time-stamped file. Path information MUST
NOT be included. A valid example is "patent123.doc". An invalid
example is "c:\Documents and settings\John\Desktop\patent123.doc".
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Compliant applications SHALL always populate the mimeType field of
TimeStampedData structure with a valid MIME content-type string. A
valid example is "application/pdf". An invalid example is "whatever".
4. Recommanded processing
When generating the TimeStampedData structure, applications are
supposed to behave like follows:
o populate the version field with the integer value v1(1);
o populate the fileName field with the real name of the file,
without path;
o populate the mimeType field with an appropriate MIME type string,
preferably, or at least with "application/octet-stream";
o populate the content field with the entire contents of the file;
o add the necessary evidence (e.g. one or more TimeStampTokens);
o insert the TimeStampedData into a ContentInfo structure, with the
id-timestamped-data OID in the contentType field;
o BER-encode the ContentInfo structure and save it with the same
name of the time-stamped file, but with the file extension
recommended in section 5.
When parsing an existing TimeStampedData structure, applications are
supposed to behave like follows:
o check that the contentType field of the ContentInfo structure has
the expected value (id-timestamped-data) in its contentType field;
then, extract the inner TimeStampedData structure and continue
processing;
o check the version field (it should be v1);
o check the fileName field (it must not be empty) and keep it for
later use;
o check the mimeType field (it must not be empty) and keep it for
later use;
o read the content field and prepare to save it in a separate file
and/or show it to the user;
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o check that the evidence field not be empty; extract the inner data
and prepare to show them to the user and/or save them to separate
files;
o validate the evidence data (e.g. in case of timeStamps: check that
each TimeStampToken does indeed contain the hash of the time-
stamped document and it was signed by a trusted TSA);
o depending on the application, show the evidence data to the user;
o depending on the application, show the time-stamped document to
the user, possibly by activating a suitable external "viewer"; if
the fileName extension is not sufficient to figure out the
suitable viewer, try using the mimeType field as an additional
hint;
o depending on the application, save the content field into a
separate file with the name specified by the fileName field (or
let the user specify the desired filename).
5. Recommended file extensions
A file containing a TimeStampedData structure SHOULD bear the .tsd
extension. Example: "patent123.tsd"
6. Security Considerations
There are no security issues.
7. IANA Considerations
This document defines one object identifier under the pkcs7 arc:
id-timestamped-data OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs7(7) 7 }
8. Acknowledgments
This document was prepared using 2-Word-v2.0.template.dot.
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9. References
[KWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
http://www.ietf.org/rfc/rfc2119.txt
[TSP] Adams, C., Cain, P., Pinkas, D. and R. Zuccherato,
"Internet X.509 Public Key Infrastructure Time-Stamp
Protocol (TSP)", RFC 3161, August 2001.
http://www.ietf.org/rfc/rfc3161.txt
[CMS] Housley, R., "Cryptographic Message Syntax (CMS)",
RFC 3852, July 2004.
http://www.ietf.org/rfc/rfc3852.txt
[MIME] Borenstein, N., and N. Freed, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
http://www.ietf.org/rfc/rfc2045.txt
Author's Addresses
Adriano Santoni
Actalis S.p.A.
Via Taramelli 26
I-20124 Milano
Phone: +39-02-68825.1
Email: adriano.santoni@actalis.it
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