Denis
----- Original Message -----
From: Denis Pinkas
To: ietf-smime(_at_)imc(_dot_)org
Cc: ietf-ltans(_at_)imc(_dot_)org ; 'Russ Housley'
Sent: Monday, January 15, 2007 6:59 AM
Subject: Re: Cross review of draft ERS from LTANS WG until Jan 23 rd
I said in an earlier e-mail: "The WG has to justify why it would not fulfill
its needs".
Carl has provided interesting information to explain the differences with ISO
ISO-18014-3
and why ERS is different. The main advantage is the use of "ordinary"
time-stamps rather
than time-stamps with specific extensions. However, this information should
not be lost
and be used to write an informative annex.
There are indeed much more important topics.
ERS is supposed to respond to draft-ietf-ltans-reqs-10.txt, isn'it ?
However, many of the requirements that are present in the requirements
document
are not met by the current ERS draft.
Here are a few examples :
1. ltans-reqs-10 defines an Archival Period as "The period during which an
archiveddata object is preserved by a long-term archive service". How may a
long term-archive service be held responsible of storing the data during that
time-period, since the information to know the time period is not present in
the ER ? Denis this is one of the key disagreement's you and I have with
timestamping. There is NO need to keep that information online or mechanically
provable in a methodology that remains consistant with any taks than proving
the signature at the time of its signing in the technology available at the
time of the signing. 2. ltans-reqs-10 defines a Cr!
yp!
tographic Maintenance Policy. There is no corresponding element in ERS. How can
a long term-archive service know which maintenance to apply, since the
information to perform the maintenance correctly is not present in ER ?
3. ltans-reqs-10 states on page 7: A long-term archive service provides
evidence that may be used to demonstrate the existence of an archived data
object at a given time and the integrity of the archived data object since that
time. The ER is supposed to be the basic piece of data to support that
evidence. However, it is not signed by the long term-archive service, thus it
cannot be used "to demonstrate the existence of an archived data object at a
given time and the integrity of the archived data object since that time".4.
ltans-reqs-10 adds on page 7: "Additionally, the evidence identifies the LTA(s)
that have participated in the preservation of the archived data object".
However, ER does not contain the names of the LTA(s) that have participated in
the preservation of the archived data object.5. ltans-reqs-10 states on page 9:
"A long-term archive service must operate in accordance with a long-term
archive service policy that defines characteristics of the implementation of
the long-term archive service". However, ER does not contain a data item to
support the "long-term archive service policy". There is no specification in
the protocol drafts that these 'policies and control features' be a part of the
mechanical processes of the LTANS service Denis...6. ltans-reqs-10 adds on page
10: " Over the course of many years, the policies under which an LTA operates
may undergo modification. Thus, an evidence record may feature multiple
indications of policies active at various points during the life of an archived
data object." However, the ER does not contain such an information.
7. ltans-reqs-10 states on page 11: "A long-term archive service must be
capable of providing evidence that can be used to demonstrate the integrity of
data for which it is responsible from the time it received the data until the
expiration of the archival period of the data". However, no data item is
specified in ER to provide this evidence.This means that much work is still
needed on the document to fulfill the requirements.
Now, let us see what should be done. The following is obviously an unpolished
strawman proposal.
In order to reduce the number of time stamps, it is necessary to be able to
aggregate data
before applying a time stamp on it. For doing it, the following structure
(close to the
structure of ArchiveTimeStamp, but different) would fulfill the need).
TimeStampedNode ::= SEQUENCE {
digestAlgorithm [0] AlgorithmIdentifier OPTIONAL,
archivalPolicy ArchivalPolicy,
archivalTimePeriod ArchivalTimePeriod,
cryptoMaintenancePolicy CryptoMaintenancePolicy,
reducedHashtree SEQUENCE OF PartialHashtree,
timeStamp TimeStampToken }
PartialHashtree ::= SEQUENCE OF OCTET STRING
ArchivalPolicy::= OBJECT IDENTIFIER
ArchivalTimePeriod ::= SEQUENCE {
notBefore GeneralizedTime,
notAfter GeneralizedTime }
CryptoMaintenancePolicy would need more work to be defined, but basically
would contain a sequence of algorithm identifiers with their parameters.
The CryptoMaintenancePolicy applies to the data in the tree and to the crypto
of
the time stamp token.
The hash included in the TimeStampToken is computed on the reducedHashtree
element.
If this structure is signed by an agent from an archival service, then it can
be used
to demonstrate that a given agent from an LTA has accepted to archive, under
a given
policy for a given time period, the data items that are under the hash tree.
This means that TimeStampedNode must be the eContent of a CMS message signed
by
an LTA agent in order to form a SignedNode.
Later on, the same, another or more LTA agents may need to add some other
data to
a signed Node, without loosing the previous time-stamp and signature.
This leads to the following structure:
EvidenceNode ::= SEQUENCE {
version INTEGER { v1(1) } ,
digestAlgorithms SEQUENCE OF AlgorithmIdentifier,
archivalPolicy ArchivalPolicy,
archivalTimePeriod ArchivalTimePeriod,
cryptoMaintenancePolicy CryptoMaintenancePolicy,
evidenceRecord EvidenceRecord,
-- the evidence record that serves
-- for the construction
signedNodeSequence SignedNodeSequence OPTIONAL,
-- the elements that are added
-- to the previous evidence
timeStamp TimeStampToken }
with:
signedNodeSequence ::= SEQUENCE OF SignedNode
The CryptoMaintenancePolicy applies to the previous evidence record, to all
the data that are in the tree and to the crypto of the time stamp token.
The hash included in the TimeStampToken is computed on the concatenation of
the
evidenceRecord element and of the signedNodeSequence element.
This means that EvidenceNode must be the eContent of a CMS message signed by
an LTA agent in order to form an EvidenceRecord.
This new proposal fulfills the seven requirements mentioned here above.
Denis
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Tony,
I think Denis should provide additional details when calling for a working
group item to be dropped, especially when making this request this late in the
process with non-freely available documents as the basis. However, I'll try to
make the case in the other direction.
I don't think it's simply a case of too many options that require profiling.
One motivation often cited during the development of ERS is support for
aggregations of data. This is represented in ERS via the reducedHashtree field
in the ArchiveTimeStamp structure. This field and the related
ArchiveTimeStampChain and ArchiveTimeStampSequence structures allow handling of
the aggregation when the initial timestamp is generated, when simple timestamp
renewal is required as well as when simple timestamp renewal is not sufficient
and the original data must be hashed again.
The ISO spec uses the ExtRenewal extension for timestamp renewal. This is
roughly analogous to the timestamp renewal feature in ERS. However, there does
not seem to be sufficient support for cases where the hash algorithm is updated
and the original data must be rehashed. In ERS, when a hash algorithm update
is necessary, the preceding timestamp tokens are hashed along with the original
data. In the ISO spec, an existing timestamp token is presented for renewal
but the original data is not. It may be possible to make this work using the
extHash extension, but I don't see any description of this in the current spec
(nor do I see any text that describes verification of the ExtRenewal
extension). I don't follow how the aggregation mechanisms in the ISO spec can
be used to aggregate data for the initial timestamp well enough to compare them
to ERS.
ERS support for aggregation is more clearly stated and ERS provides more
complete handling of renewal operations. For these reasons, I think we should
proceed with ERS instead of trying to enhance the ISO spec.
Carl
----------------------------------------------------------------------------
From: Tony Capel [mailto:capel(_at_)comgate(_dot_)com]
Sent: Thursday, January 11, 2007 11:04 AM
To: 'Carl Wallace'; 'Denis Pinkas'; ietf-smime(_at_)imc(_dot_)org
Cc: ietf-ltans(_at_)imc(_dot_)org; 'Tobias Gondrom'; 'Russ Housley'
Subject: RE: RE: RE: Cross review of draft ERS from LTANS WG - RE: WG Last
Ca ll:draft-ietf-ltans-ers-09.txt- untilJan 23rd
Carl:
I think Denis asks simply for the justification for the introduction of new
technology to solve a problem which may already be solved with an existing ISO
standard (which has already been published and is presumably more mature than
what is being proposed).
Denis notes (in his previous comment) that perhaps the ISO standard offers
too many options and that perhaps a Profile of this ISO standard might be
published as an RFC to tailor the ISO standard for the specific application(s)
you have in mind. In such a case the RFC should profile (see ISO/IEC TR10000)
the ISO standard and not introduce new technology.
Tony
-----Original Message-----
From: owner-ietf-smime(_at_)mail(_dot_)imc(_dot_)org
[mailto:owner-ietf-smime(_at_)mail(_dot_)imc(_dot_)org] On Behalf Of Carl
Wallace
Sent: January 11, 2007 10:16 AM
To: Denis Pinkas; ietf-smime(_at_)imc(_dot_)org
Cc: ietf-ltans(_at_)imc(_dot_)org; Tobias Gondrom; Russ Housley
Subject: RE: RE: RE: Cross review of draft ERS from LTANS WG - RE: WG Last
Ca ll:draft-ietf-ltans-ers-09.txt- untilJan 23rd
My response wasn't a reversal of the question but a request for details.
Folks on the list have previously discussed these specifications, including
their use within an EvidenceRecord. You made a sweeping comment that lacked
any details and called for fairly drastic measures. I simply asked for
justification.
--------------------------------------------------------------------------
From: Denis Pinkas [mailto:denis(_dot_)pinkas(_at_)bull(_dot_)net]
Sent: Thursday, January 11, 2007 9:46 AM
To: Carl Wallace; ietf-smime(_at_)imc(_dot_)org
Cc: ietf-ltans(_at_)imc(_dot_)org; Russ Housley; Tobias Gondrom
Subject: Re: RE: RE: Cross review of draft ERS from LTANS WG - RE: WG
Last Ca ll:draft-ietf-ltans-ers-09.txt- untilJan 23rd
Carl,
Please do not reverse the question. ISO 18014-3 already exists. The WG
has to justify why it would not fulfill its needs.
I will refine my question: Why is a profile of ISO 18014-3 not adequate
to fulfill the needs ?
A profile would make sense, since ISO 18014-3 has many options.
Denis
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