Re: [STDS-802-11] document 11-14/1104r1 for TGmc

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On Thu, Sep 18, 2014 at 1:01 AM, Jon Rosdahl <jrosdahl@xxxxxxxx> wrote:

--- This message came from the IEEE 802.11 Working Group Reflector ---
Hi Dan,
   As doc 11-14/1104r1 has a lot of CIDs, it took a bit of reading to find where your concern area was in the document. (for those reading along it is I believe CID 3432, 3426, 3427, 3429).

I am confused in reading 11-14/1104r1 on these CIDs because it does not seem consistent in the naming.
Is it supposed to be SHA1 or SHA-1 for example (as you note).

So to help those of us that do not work with the security protocols daily, what is the appropriate names...can we safely say that it is supposed to be SHA1, SHA256, SHA128.
Given the nominal names then I understand from your suggestion that the "-xxx" is then the amount to truncate to. (without the word truncate to prefix the name).

The other parts that are noted as needing to be change you do not comment on.
Do we need to say "delete securely" in all cases or is "delete" sufficient.
does "destroy" imply "delete securely" and thus it is a valid term to use, and should be used when ever we mean "delete securely"
Thanks,
Jon

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Jon Rosdahl                    Senior Standards Architect
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On Thu, Sep 18, 2014 at 1:14 AM, Dan Harkins <dharkins@xxxxxxxxxxxxxxxxx> wrote:
--- This message came from the IEEE 802.11 Working Group Reflector ---

Hello,

I may not be at the 11mc session where 11-14/1104r1 is presented so I

want to get discussion on it started on the mailing list.

There are some issues with the proposed description of various designations

of the Secure Hash Algorithm family of hash functions. In an effort to obtain

what the author views as "consistency" he has introduced ambiguity and,

in my opinion, incorrectness.

There are 3 families of the Secure Hash Algorithm. There's the 1st family of

SHA, (which is just designated SHA1) and there's the 2nd family of SHA (known

as SHA2) which is SHA256 and SHA512, including truncated versions of each,

SHA224 is a truncated version of SHA256 and SHA384 is a truncated version of

SHA512. The 3rd family of SHA, SHA3 is a weird beast that we don't need to

trouble ourselves with since we're not using it.

It is important to understand, though, that SHA1, SHA256, and SHA512 are

different. They are not just truncated versions of the same function. And while

SHA256 does actually produce 256-bits of digest output, SHA1 does not

produce 1-bit of digest output, it produces 160-bits. But we (802.11) do

truncate the output of SHA family hash functions. For instance, we sometimes

want only the first 128-bits of SHA1. Just to make things more complicated,

we also use the HMAC construct with a SHA family algorithm.

So how to deal with identifying the appropriate algorithm in the appropriate

family of SHA, whether it is alone or as HMAC, and how to identify the particular

output bit length that we are concerned with? 11-14/1104r1 does a poor job.

Let me propose a better way:

* the particular algorithm of the family is used without any hyphens— for

example, it's SHA256 not SHA-256, and it's SHA1 always.

* when we want to truncate we add a hyphen and indicate the bit length we

want to use— for example, it's SHA256-128 (not sure why we'd do this but it's

an example) or SHA1-128.

* if we don't add a hyphen and number indicating truncation then the entire

length of the algorithm output is used.

* if we want to use the HMAC construct we prepend "HMAC-" to the SHA family

algorithm indicated, including any possible indication of truncation— for

example, HMAC-SHA256 or HMAC-SHA1-128.

* if we don't prepend "HMAC-" then we are using the algorithm directly, and

not as a keyed hash function.

While 11-14/1104r1 does this correct in some cases— it proposes to

change "HMAC-SHA-256" to "HMAC-SHA256"-- it does it wrong in other

cases— it proposes to change "SHA1" to "SHA-1".

Also, if we adopt this more correct way of referring to these various

incarnations of hashing we do not need to say something like

"Truncate-128(HMAC-SHA1(xxx))" we just say HMAC-SHA1-128(xxx)".

Minor grammatical gripe: there is no such algorithm called

"HMAC-SHA1-64", or even "HMAC-SHA-1-64" so we should not be using

the definite article when describing the use of SHA1 in an HMAC

construct while truncating the output to 64 bits.

Please modify 11-14/1104r1 to adopt this more correct terminology

before it gets adopted.

regards,

Dan.

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