Re: [ltans] I-D Action:draft-ietf-ltans-dssc-12.txt

<ErnstG.Giessmann@t-systems.com> Thu, 01 October 2009 08:38 UTC

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Subject: Re: [ltans] I-D Action:draft-ietf-ltans-dssc-12.txt
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Hi Bill and Carl,

first remark:
you wrote
> GeneralizedTime IMHO is better than Time

but such a comparison is a bit wrong, because Time is a CHOICE type and GeneralizedTime an ASN.1 built-in type. You can always use your lovely GeneralizedTime also with the Time type, e.g.:

 LTANSValidity ::= SEQUENCE {
   start  [0] Time OPTIONAL,  -- GeneralizedTime MAY be used
   end    [1] Time OPTIONAL   -- GeneralizedTime SHOULD be used
   }

second:
Could you really give an example of an crypto algo that "has an indefinite end time"? And then you should include this example in your Appendix E.
Keeping in consideration the environmental destruction I guess that you can also use for this purpose the year 2100.

third:
I'm not sure about my level of understanding. Could you give me an example of cryptographic algorithm parameters (e.g. for RSA) which are unsuitable today but will become suitable next year? Anyway you should include such an
example in your Appendix E as well.

If you insist of having a start time, what about:

 LTANSValidity ::= SEQUENCE {
   expectedEOV     GeneralizedTime, 
   beginOfValidity GeneralizedTime OPTIONAL 
   }

based on a required suitability end time estimation (cf. section 1.1).

Concerning your remark on Extension type definition I would like to point out that the critical field in the RFC5280 definition is a DEFAULT value, so you can always drop it if you wish:

-- Extension  ::=  SEQUENCE  {
--      extnID      OBJECT IDENTIFIER,
--      critical    BOOLEAN DEFAULT FALSE,
--      extnValue   OCTET STRING

text proposal:

There is no use case for the critical BOOLEAN field in the imported from PKIX1Explicit88 definition of the Extension type, therefore conforming implementations SHOULD NOT/MUST NOT include it in a Evaluation object.

Even if this is not acceptable for you, you should rethink your definition and not only the naming. IMHO the encapsulating another structure is better then the deprecated ANY type.

Regards,
Ernst.


Carl Wallace schrieb:
> I think the name change suggestion is fine.  This can be handled during the AUTH48 period for this draft, which cleared IESG review today as this draft addressed the last of the issues.
> 
>> -----Original Message-----
>> From: ltans-bounces@ietf.org [mailto:ltans-bounces@ietf.org] On Behalf
>> Of Bill Russell
>> Sent: Wednesday, September 30, 2009 11:39 AM
>> To: ErnstG.Giessmann@t-systems.com; ltans@ietf.org
>> Subject: Re: [ltans] I-D Action:draft-ietf-ltans-dssc-12.txt
>>
>> I propose that we just change the name in our draft but keep the new
>> definitions. For the Validity, GeneralizedTime IMHO is better than
>> Time, since the current year would still code as UTCTime as part of
>> that def (making it a two digit year rather than four until something
>> like 2050). And, if there is no use for a criticality field, there is
>> no sense in reusing that definition for extensions.
>>
>> -----Original Message-----
>> From: ltans-bounces@ietf.org [mailto:ltans-bounces@ietf.org] On Behalf
>> Of ErnstG.Giessmann@t-systems.com
>> Sent: Wednesday, September 30, 2009 10:11 AM
>> To: ltans@ietf.org
>> Subject: Re: [ltans] I-D Action:draft-ietf-ltans-dssc-12.txt
>>
>> Hi all,
>> there are some clashes in the ASN.1 code of the draft that prevents to
>> use it with e.g. RFC3280/RFC5280.
>>
>> 1.
>> The Draft defines
>> -- Extension ::= SEQUENCE {
>> --   extensionType           OBJECT IDENTIFIER,
>> --   extension               ANY DEFINED BY extensionType
>> --   }
>>
>> which has a (presumably better defined) twin in RFC5280:
>> Extension  ::=  SEQUENCE  {
>>      extnID      OBJECT IDENTIFIER,
>>      critical    BOOLEAN DEFAULT FALSE,
>>      extnValue   OCTET STRING
>>                  -- contains the DER encoding of an ASN.1 value
>>                  -- corresponding to the extension type identified
>>                  -- by extnID
>>      }
>>
>> I suggest to import the type Extension from PKIX1Explicit88. Please
>> take into account that already since 1997 the ASN.1 types ANY/ANY
>> DEFINED BY are deprecated (http://www.itu.int/ITU-
>> T/studygroups/com07/changing-ASN.html).
>>
>>
>> 2.
>> The Draft defines
>> -- Validity ::= SEQUENCE {
>> --   start  [0] GeneralizedTime OPTIONAL,
>> --   end    [1] GeneralizedTime OPTIONAL
>> --   }
>>
>> which clashes also with a twin in RFC3280/RFC5280:
>>
>> Validity ::= SEQUENCE {
>>      notBefore      Time,
>>      notAfter       Time  }
>>
>> It seems to me that this is based on a misunderstanding already in
>> section 1.1 (Motivation)
>>
>>    Cryptographic algorithms that are used in signatures shall be
>>    selected to resist such attacks during their period of use.  For
>>    signature keys included in public key certificates, it is the
>>    validity period of the certificate.  Cryptographic algorithms that
>>    are used for encryption shall resist during the time during which it
>>    is planned to keep the information confidential.
>>
>> The validity period of a certificate is primarily *not* a period where
>> resistance against attacks is assured but "is the time interval during
>> which the CA warrants that it will maintain information about the
>> status of the certificate". If the signatures are made in a
>> authentication context, then the validity is almost the same as the
>> usage time. But if the signatures are related to a non-repudiation
>> context then the documented in the certificate validity time may be
>> longer then predicted at time of certificate generation. If the
>> algorithm becomes weaker then the certificate can be easily revoked,
>> which reduces the "usage time" immediately, leaving the "warranty time"
>> unchanged. If on the other side it turned out that the algorithm is
>> harder than predicted, it is not necessary to revoke the certificate
>> based on a still secure algorithm.
>>
>> Just another thought: For a certificate the dates notBefore and
>> notAfter make sense. But how we understand the notBefore date for
>> algorithm resistance? A certificate may become valid later, but how a
>> weak algorithm may become hard after a while?
>>
>> I would suggest to remove the Validity type and replace it by a single
>> notAfter date.
>>
>> Regards,
>> Ernst.
>> --
>> 	Ernst G Giessmann
>> 	T-Systems Enterprise Services GmbH
>> 	ICT Operations
>> 	Security and Smart Card Solutions
>> 	Goslarer Ufer 35, D-10589 Berlin
>> 	tel:+49-30-3497-4342
>>
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>>> -----Ursprüngliche Nachricht-----
>>> Von: ltans-bounces@ietf.org [mailto:ltans-bounces@ietf.org]
>>> Im Auftrag von Internet-Drafts@ietf.org
>>> Gesendet: Mittwoch, 30. September 2009 10:00
>>> An: i-d-announce@ietf.org
>>> Cc: ltans@ietf.org
>>> Betreff: [ltans] I-D Action:draft-ietf-ltans-dssc-12.txt
>>>
>>> A New Internet-Draft is available from the on-line
>>> Internet-Drafts directories.
>>> This draft is a work item of the Long-Term Archive and Notary
>>> Services Working Group of the IETF.
>>>
>>>
>>> 	Title           : Data Structure for the Security
>>> Suitability of Cryptographic Algorithms (DSSC)
>>> 	Author(s)       : T. Kunz, et al.
>>> 	Filename        : draft-ietf-ltans-dssc-12.txt
>>> 	Pages           : 48
>>> 	Date            : 2009-09-30
>>>
>>> Since cryptographic algorithms can become weak over the
>>> years, it is necessary to evaluate their security
>>> suitability.  When signing or verifying data, or when
>>> encrypting or decrypting data, these evaluations must be
>>> considered.  This document specifies a data structure that
>>> enables an automated analysis of the security suitability of
>>> a given cryptographic algorithm at a given point of time
>>> which may be in the past, at the present time or in the
>>> future.Conventions used in this document
>> ...
>>> A URL for this Internet-Draft is:
>>> http://www.ietf.org/internet-drafts/draft-ietf-ltans-dssc-12.txt
>> ...
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