Re: [OAUTH-WG] PKCE: SHA256(WAT?)

[John Bradley <[e-mail]>]

Have a look at the latest version I added OCTETS(STRING) to show the conversion.   ASCII(STRING) seemed more confusing by drawing character encoding back in.

I was tempted to call it a octet array without the terminating NULL of STRING but didn’t want to introduce array.

Let me know what you think.

> On Jan 30, 2015, at 1:56 PM, Brian Campbell <[e-mail]> wrote:
> 
> But, while it may be clear to you, what I'm saying here is that it's not clear to a reader/implementer.
> 
> Somehow the conversion from a character string to an octet string needs to be clearly and unambiguously stated. It doesn't have to be the text I suggested but it's not sufficient as it is now.
> 
> Something like this might work, if you don't want to touch the parts in 4.2 and 4.6: "SHA256(STRING) denotes a SHA2 256bit hash [RFC6234] of the octets of the ASCII [RFC0020] representation of STRING."
> 
> An "octet sequence using the url and filename safe Alphabet [...], with length less than 128 characters." is ambiguous. Octets and characters are intermixed with no mention of encoding. But they're not interchangeable. 
> 
> 
> On Fri, Jan 30, 2015 at 7:15 AM, Nat Sakimura <[e-mail] <mailto:[e-mail]>> wrote:
> I do not think we need ASCII(). It is quite clear without it, I suppose. 
> 
> In 4.1, I would rather do like: 
> 
>  code_verifier = high entropy cryptographic random 
>    octet sequence using the url and filename safe Alphabet [A-Z] / [a-z]
>    / [0-9] / "-" / "_" from Sec 5 of RFC 4648 [RFC4648], with length
>    less than 128 characters.
> 
> Nat
> 
> 2015-01-30 22:51 GMT+09:00 Brian Campbell <[e-mail] <mailto:[e-mail]>>:
> That's definitely an improvement (to me anyway). 
> 
> Checking that the rest of the document uses those notations appropriately, I think, yields a few other changes. And probably begs for the "ASCII(STRING) denotes the octets of the ASCII representation of STRING" notation/function, or something like it, to be put back in. Those changes might look like the following:
> 
> 
> In 4.1.: 
> 
> OLD:
>    code_verifier = high entropy cryptographic random ASCII [RFC0020]
>    octet sequence using the url and filename safe Alphabet [A-Z] / [a-z]
>    / [0-9] / "-" / "_" from Sec 5 of RFC 4648 [RFC4648], with length
>    less than 128 characters.
> 
> NEW (maybe):
>   code_verifier = high entropy cryptographically strong random STRING
>   using the url and filename safe Alphabet [A-Z] / [a-z]
>    / [0-9] / "-" / "_" from Sec 5 of RFC 4648 [RFC4648], with length
>    less than 128 characters.
> 
> 
> In 4.2.: 
> 
> OLD:
>    S256  "code_challenge" = BASE64URL(SHA256("code_verifier"))
> 
> NEW (maybe):
>    S256  "code_challenge" = BASE64URL(SHA256(ASCII("code_verifier")))
> 
> 
> In 4.6.: 
> 
> OLD:
>    SHA256("code_verifier" ) == BASE64URL-DECODE("code_challenge").
> 
> NEW (maybe):
>    SHA256(ASCII("code_verifier")) == BASE64URL-DECODE("code_challenge").
> 
> 
> 
> 
> On Thu, Jan 29, 2015 at 8:37 PM, Nat Sakimura (=nat) <[e-mail] <mailto:[e-mail]>> wrote:
> I take your point, Brian. 
> 
> In our most recent manuscript, STRING is defined inside ASCII(STRING) as 
> 
> STRING is a sequence of zero or more ASCII characters
> 
> but it is kind of circular, and we do not seem to use ASCII(). 
> 
> What about re-writing the section like below? 
> 
> STRING denotes a sequence of zero or more ASCII  [RFC0020] <http://xml2rfc.ietf.org/cgi-bin/xml2rfc.cgi#RFC0020> characters. 
> 
> OCTETS denotes a sequence of zero or more octets. 
> 
> BASE64URL(OCTETS) denotes the base64url encoding of OCTETS, per Section 3 <http://xml2rfc.ietf.org/cgi-bin/xml2rfc.cgi#Terminology> producing a ASCII[RFC0020] <http://xml2rfc.ietf.org/cgi-bin/xml2rfc.cgi#RFC0020> STRING.
> 
> BASE64URL-DECODE(STRING) denotes the base64url decoding of STRING, per Section 3 <http://xml2rfc.ietf.org/cgi-bin/xml2rfc.cgi#Terminology>, producing a sequence of octets.
> 
> SHA256(OCTETS) denotes a SHA2 256bit hash [RFC6234] <http://xml2rfc.ietf.org/cgi-bin/xml2rfc.cgi#RFC6234> of OCTETS.
> 
> 
> 
> 
> 
> 
> 
>> On Jan 30, 2015, at 08:15, Brian Campbell <[e-mail] <mailto:[e-mail]>> wrote:
>> 
>> In §2 [1] we've got "SHA256(STRING) denotes a SHA2 256bit hash [RFC6234] of STRING." 
>> 
>> But, in the little cow town where I come from anyway, you hash bits/octets not character strings (BTW, "STRING" isn't defined anywhere but it's kind of implied that it's a string of characters).  
>> 
>> Should it say something more like "SHA256(STRING) denotes a SHA2 256bit hash [RFC6234] of the octets of the ASCII [RFC0020] representation of STRING."? 
>> 
>> I know it's kind of pedantic but I find it kind of confusing because the code_verifier uses the url and filename safe alphabet, which has me second guessing if SHA256(STRING) actually means a hash of the octet produced by base64url decoding the string. 
>> 
>> Maybe it's just me but, when reading the text, I find the transform process to be much more confusing than I think it needs to be. Removing and clarifying some things will help. I hate to suggest this but maybe an example showing the computation steps on both ends would be helpful?
>> 
>> Also "UTF8(STRING)" and "ASCII(STRING)" notations are defined in §2 but not used anywhere.
>> 
>> And §2 also says, "BASE64URL-DECODE(STRING) denotes the base64url decoding of STRING, per Section 3, producing a UTF-8 sequence of octets." But what is a UTF-8 sequence of octets? Isn't it just a sequence octets? The [RFC3629] reference, I think, could be removed.
>> 
>> [1] https://tools.ietf.org/html/draft-ietf-oauth-spop-06#section-2 <https://tools.ietf.org/html/draft-ietf-oauth-spop-06#section-2>
> 
> Nat Sakimura
> [e-mail] <mailto:[e-mail]>
> 
> 
> 
> 
> 
> 
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> 
> 
> -- 
> Nat Sakimura (=nat)
> Chairman, OpenID Foundation
> http://nat.sakimura.org/ <http://nat.sakimura.org/>
> @_nat_en
>