Re: [kitten] shepherd review of draft-aes-cts-hmac-sha2-09
Stephen Farrell <stephen.farrell@cs.tcd.ie> Sun, 03 July 2016 09:57 UTC
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To: Jeffrey Altman <jaltman@secure-endpoints.com>, Luke Howard <lukeh@padl.com>, Benjamin Kaduk <kaduk@MIT.EDU>
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From: Stephen Farrell <stephen.farrell@cs.tcd.ie>
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Cc: kitten@ietf.org, draft-ietf-kitten-aes-cts-hmac-sha2@tools.ietf.org
Subject: Re: [kitten] shepherd review of draft-aes-cts-hmac-sha2-09
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Hiya, I nearly just started the IETF last call for this, but then noticed these emails;-) Please ignore any status change emails you may have seen. Chairs - please tell me when you want me to start IETF LC. I did my AD review of it, and modulo this discussion being resolved, I think it's ready to go ahead. Thanks, S. On 28/06/16 12:58, Jeffrey Altman wrote: > +1 > > On 6/28/2016 3:21 AM, Luke Howard wrote: >> I reckon let's do it "properly" even if at the expense of redundant text. >> >> Sent from my iPhone >> >>> On 28 Jun 2016, at 11:49, Benjamin Kaduk <kaduk@MIT.EDU> wrote: >>> >>> Thanks, Michael. >>> >>> If the WG does want to treat the PRF octet-string input as a SP800-108 >>> context and use a zero-byte separator, it seems like the "quick-and-dirty" >>> patch would be to just stick one in after "prf" and then there would be >>> another (somewhat superfluous) one appended after the octet-string by >>> KDF-HMAC-SHA2. That might be easier than essentially inlining the >>> definitino of KDF-HMAC-SHA2 for just the PRF calculation. >>> >>> -Ben >>> >>>> On Mon, 27 Jun 2016, Michael Jenkins wrote: >>>> >>>> Ben, >>>> >>>> we'll get started on these. >>>> >>>>> On Sun, Jun 26, 2016 at 11:03 PM, Benjamin Kaduk <kaduk@mit.edu> wrote: >>>>> >>>>> Hi Michael et al, >>>>> >>>>> As I was preparing the shepherd writeup for this document, I noticed some >>>>> things that do not block the progression of the document but do require >>>>> changes, and one item that may require further WG input. Can you prepare >>>>> a new version with the changes mentioned below? >>>>> >>>>> The one item which would potentially affect the actual protocol: at the >>>>> end of Section 5, the pseudo-random function seems to be using a SP800-108 >>>>> KDF but omits the zero byte between label and context. I think it would >>>>> be better to have the zero byte -- do you remember whether there was a >>>>> reason to omit it? (Adding the zero byte would require re-rolling some >>>>> test vectors, to be clear.) >>>>> >>>>> Additionally, all document authors will need to confirm compliance with >>>>> BCPs 78 and 79 for this document, namely that there are no intellectual >>>>> property concerns with the document that are not already disclosed. >>>>> >>>>> Please add a normative reference to RFC 2104 for HMAC, first mentioned at >>>>> the end of Section 1. >>>>> >>>>> In Section 3, it might aid clarity to mention that the 0x00000001 input to >>>>> HMAC() is the 'i' parameter from SP800-108 [indicating that this is the >>>>> first block of output, even though it is the only block of output as >>>>> well]. >>>>> >>>>> In Section 4, it might be worth re-mentioning "where PBKDF2 is the >>>>> function of that name from RFC 2898" after the algorithm block, since most >>>>> everything else used there also gets clarified. (It is already cited at >>>>> the beginning of the section, in the overview paragraph.) >>>>> >>>>> The document should be consistent about using "cipher state" as one word >>>>> or two (RFC 3961 prefers the two-word form). It also makes a rather >>>>> sudden appearance at the beginning of Section 5 with no explanatory >>>>> introduction; it might help the reader to instead start with "The RFC 3961 >>>>> cipher state that maintains cryptographic state across different >>>>> encryption operations using the same key is used as the formal >>>>> initialization vector [...]" On the next page, "cipherstate" is defined as >>>>> "a 128-bit initialization vector derived from the ciphertext", which is >>>>> potentially misleading, since it can't be both used as the IV for and >>>>> derived from the same ciphertext! Probably it's better to say "derived >>>>> from a previous (if any) ciphertext using the same encryption key, as >>>>> specified below". >>>>> >>>>> Still in Section 5, in the definition of the encryption function (well, >>>>> computing the cipherstate, really), I'm of two minds whether it's worth >>>>> mentioning that the case of L < 128 is impossible because of the 128-bit >>>>> confounder. >>>>> >>>>> In the decryption function, can you add a note to the right of "(C, H) = >>>>> ciphertext" that "[H is the last h bits of the ciphertext]"? >>>>> >>>>> In the pseudo-random function, please replace "base-key" with "input-key", >>>>> since the key input to the PRF is not expected to be a kerberos protocol >>>>> long-term base key. >>>>> >>>>> In Section 6, the "associated cryptosystem"s are supposed to be >>>>> "AES-128-CTS" or "AES-256-CTS", but those strings do not appear elsewhere >>>>> in the document. While the meaning is pretty clear, it's probably better >>>>> to just say "aes128-cts-hmac-sha256-128 or aes256-cts-hmac-sha384-192 as >>>>> appropriate". This does duplicate the preceding text, but we do want to >>>>> explicitly list the "associated encryption algorithm" as listed in the >>>>> Checksum Algorithm Profile of Section 4 of RFC 3961. >>>>> >>>>> In Section 8.1, the acronym "TGT" is used, the only instance in the >>>>> document. It's also potentially misleading, since ticket-granting tickets >>>>> are generally objects that are issued to client principals by the AS. >>>>> I'd go with "Cross-realm krbtgt keys" instead. >>>>> >>>>> The test vectors for key derivation have a parenthetical "constant = >>>>> 0x...", but the term "constant" does not appear elsewhere in the document. >>>>> The hex values are the label input for the HMAC, so we should call them >>>>> that. >>>>> >>>>> >>>>> Thanks, >>>>> >>>>> Ben >>>> >>>> >>>> >>>> -- >>>> Mike Jenkins >>>> mjjenki@tycho.ncsc.mil - if you want me to read it only at my desk >>>> m.jenkins.364706@gmail.com - to read everywhere >>>> 443-634-3951 >>> >>> _______________________________________________ >>> Kitten mailing list >>> Kitten@ietf.org >>> https://www.ietf.org/mailman/listinfo/kitten >> >> _______________________________________________ >> Kitten mailing list >> Kitten@ietf.org >> https://www.ietf.org/mailman/listinfo/kitten >> > > > > _______________________________________________ > Kitten mailing list > Kitten@ietf.org > https://www.ietf.org/mailman/listinfo/kitten >
- Re: [kitten] shepherd review of draft-aes-cts-hma… Jeffrey Altman
- Re: [kitten] shepherd review of draft-aes-cts-hma… Matt Miller (mamille2)
- Re: [kitten] shepherd review of draft-aes-cts-hma… Stephen Farrell
- Re: [kitten] shepherd review of draft-aes-cts-hma… Jeffrey Altman
- Re: [kitten] shepherd review of draft-aes-cts-hma… Luke Howard
- Re: [kitten] shepherd review of draft-aes-cts-hma… Benjamin Kaduk
- Re: [kitten] shepherd review of draft-aes-cts-hma… Benjamin Kaduk
- Re: [kitten] shepherd review of draft-aes-cts-hma… Luke Howard
- Re: [kitten] shepherd review of draft-aes-cts-hma… Michael Jenkins
- Re: [kitten] shepherd review of draft-aes-cts-hma… Benjamin Kaduk
- Re: [kitten] shepherd review of draft-aes-cts-hma… Luke Howard
- [kitten] shepherd review of draft-aes-cts-hmac-sh… Benjamin Kaduk