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 ?
2. ltans-reqs-10 defines a Cryptographic 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?.
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
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