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Re: Cross review of draft ERS from LTANS WG until Jan 23 rd

2007-01-15 08:40:58
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