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RE: Gen-ART Review of draft-ietf-smime-sha2-03.txt

2008-03-01 08:28:14

Thanks for taking the time to read the draft. Responses are inline.


-----Original Message-----
From: Spencer Dawkins [mailto:spencer(_at_)wonderhamster(_dot_)org] 
Sent: Friday, February 29, 2008 12:27 AM
To: General Area Review Team
Cc: Sean Turner; Blake Ramsdell; ietf(_at_)ietf(_dot_)org; 
Subject: Gen-ART Review of draft-ietf-smime-sha2-03.txt

I have been selected as the General Area Review Team (Gen-ART) 
reviewer for this draft (for background on Gen-ART, please see

Please resolve these comments along with any other Last Call 
comments you may receive.

Will do.

Document: draft-ietf-smime-sha2-03.txt
Reviewer: Spencer Dawkins
Review Date: 2008 02 28
IETF LC End Date: 2008-03-07
IESG Telechat date: (if known)

Summary: This document isn't ready for publication as a 
Proposed Standard - it's got enough cut-and-paste errors and 
apparently-omitted text that I'd think twice about trying to 
implement it. And if it has a note that says "normative 
reference still in progress, should be brought in line with 
normative reference before publishing as an RFC", I'm not sure 
why it's being last called now (of course, that decision is 
above my pay grade).

Wrt the reference, that draft is being worked in PKIX. Hopefully, it will
progress quickly - I'm hoping for this summer (or sooner) for it to complete
WG LC and IETF LC.  Also, the reference is for object identifiers all of
which were assigned years ago and are stable.


Please include any nits listed in
that I may have missed in this review, by reference :-(

Will do.

When one of the last call comments is "There are obvious 
errors (intentionnaly left by the editor in order to know how 
many people read the document)", this does not inspire 
confidence. I note there is no shepherd writeup in the tracker 
yet. The "of for" typo below has been in every version since 
00. Who else has read this draft?

This was, I believe, his attempt at humor. See my response to Denis' email.


  This document describes the conventions for using the message digest
  algorithms SHA-224, SHA-256, SHA-384, SHA-512, as defined in FIPS

Nit - I'm not sure what passes for normal in security drafts, 
but I'd expect to see SHA and FIPS expanded on first use in 
the abstract, and in the introduction of the document. Ditto 
for DSA, RSA, and ECDSA.

I will expand the acronyms.

  180-3, with the Cryptographic Message Syntax (CMS). It also 
  the conventions for using these algorithms with CMS and the 
  and ECDSA signature algorithms.

Conventions used in this document

Nit - it is odd to see this section as part of the abstract...

For some reason the tool picks up this section as part of the abstract. It's
got a heading title so I don't think it's in the abstract.

1. Introduction

  This document specifies the algorithm identifiers and specifies
  parameters for the message digest algorithms SHA-224, SHA-256, SHA-
  384, and SHA-512 for use with the Cryptographic Message Syntax (CMS)
  [RFC3852].  The message digest algorithms are defined in and [SHS].

Concern: "in and" seems to be missing something.

Denis caught this too. Will fix by removing the "and".

  If an implementation chooses to support one of the algorithms
  discussed in this document, then the implementation MUST do so as
  described in this document.

Concern: this MUST (and the parallel MUST in the next 
paragraph) seem odd - do you need to say this?

Hmmm ... I guess not.  I'll remove both sentences.

  Note that [RFC4231] specifies the conventions for use of for the

Concern: "of for" seems to be missing something.

I will remove "for use of" so the sentence will read: Note that [RFC4231]
specifies the conventions for the message authentication code (MAC)
algorithms ....

  message authentication code (MAC) algorithms: HMAC with 
  with SHA-256, HMAC with SHA-384, and HMAC with SHA-512.

2. Message Digest Algorithms

  The following addresses the parameters field:

Nit - this sentence isn't clear and isn't required. I'd strike it.


  There are two possible encodings for the SHA AlgorithmIdentifier
  parameters field.  The two alternatives arise from the fact 
that when
  the 1988 syntax for AlgorithmIdentifier was translated into the 1997
  syntax, the OPTIONAL associated with the AlgorithmIdentifier
  parameters got lost.  Later the OPTIONAL was recovered via a defect
  report, but by then many people thought that algorithm parameters
  were mandatory.  Because of this history some implementations encode
  parameters as a NULL element and others omit them entirely.  The
  correct encoding is to omit the parameters field; however,
  implementations MUST also handle a SHA AlgorithmIdentifier 
  field which contains a NULL.

Nit - I'd describe the normative behavior, and then provide 
the history (in a separate paragraph), just so implementers 
don't have to scan history looking for normative behavior.

Since this is an update to RFC3370 and we want the same algorithm parameters
I copied the text directly from there. I'd like to keep it the same so
implementers know that there's nothing new.

Concern - the MUST in this paragraph duplicates clearer 
normative text in the next paragraph. I'd remove the last sentence.

See above.

  The AlgorithmIdentifier parameters field is OPTIONAL.  If present,
  the parameters field MUST contain a NULL.  Implementations MUST
  accept SHA2 AlgorithmIdentifiers with absent parameters.
  Implementations MUST accept SHA2 AlgorithmIdentifiers with NULL
  parameters.  Implementations SHOULD generate SHA2
  AlgorithmIdentifiers with absent parameters.

2.4. SHA-512

  The SHA-256 message digest algorithm is defined in [SHS].  The

Concern - SHA-512, right?

Denis caught this one too. It will be fixed.

  algorithm identifier for SHA-512 is:

    id-sha512 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101)
      csor(3) nistalgorithm(4) hashalgs(2) 3 }

  The parameters are as specified in Section 2.

3. Signature Algorithms

  This section specifies the conventions employed by CMS
  implementations that support DSA [DSS], ECDSA [X9.62], and RSA
  [RFC2313] with SHA2 algorithms.

Nit - why wait until this late in the document to provide 
these references? 
The algorithms have been mentioned a bunch of times without 
them. Move them to the Introduction?

Will move them to the introduction.

  NOTE [to be removed upon publication as an RFC]: NIST has not yet
  finalized FIPS 186-3 and there is a chance that the draft may be
  changed.  This may result in differences between what is documented
  in the current version of this document and what is in the FIPS.  It
  is intended to synchronize the final version of this draft with the
  FIPS before publication as an RFC.

Concern: why is this document being Last Called now, if the 
expectation is that it's going into REF-WAIT and may change 
before it's published?

The WG wanted the note to be safe - The parts of FIPS PUB 186-3 that we use
has little chance of changing.

3.1. DSA

  The algorithm identifier for DSA with SHA-224 signature values is:

Concern: SHA-256, right?


    id-dsa-with-sha256 OBJECT IDENTIFIER ::=  { joint-iso-ccitt(2)
      country(16) us(840) organization(1) gov(101) csor(3)
      algorithms(4) id-dsa-with-sha2(3) 2 }

  When either of these algorithm identifiers is used, the
  AlgorithmIdentifier parameters field MUST be absent.

3.3. ECDSA

6. References

6.1. Normative References

  [RFC2313]   Kaliski, B., "PKCS #1: RSA Encryption Version 1.5", RFC
              2313, March 1998.

Concern: ID Nits says "** Obsolete normative reference: RFC 
2313 (Obsoleted by RFC 2437)" 

I saw this in the nits tools and decided to not update it (note there's also
RFC3447 that obsoletes 2437). RFC 2437/3447 include a description of
RSAPSS/OAEP that in my opinion (and some others) makes it harder to find the
v1.5 signature scheme. Since we don't use RSAPSS/OAEP I figured it's all
right to keep the reference to RFC 2313. Since this is an update to RFC 3370
(which was published 4 years after RFC 2437) and RFC 3370 still references
RFC 2313, I also figured it would be okay to not update the reference.


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