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

[Brian Campbell <[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]>
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]>
> 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
>
>
> Nat Sakimura
> [e-mail]
>
>
>
>
>
>