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

Brian Campbell <bcampbell@pingidentity.com> Fri, 30 January 2015 20:16 UTC

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From: Brian Campbell <bcampbell@pingidentity.com>
Date: Fri, 30 Jan 2015 13:15:42 -0700
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To: Mike Jones <Michael.Jones@microsoft.com>
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Cc: oauth <oauth@ietf.org>, Naveen Agarwal <naa@google.com>
Subject: Re: [OAUTH-WG] PKCE: SHA256(WAT?)
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I agree with Mike here. Though PKCE only needs the ASCII(STRING) one.

On Fri, Jan 30, 2015 at 12:38 PM, Mike Jones <Michael.Jones@microsoft.com>
wrote:

>
> http://tools.ietf.org/html/draft-ietf-jose-json-web-signature-41#section-1.1
> uses this notation:
>
>
>
>    UTF8(STRING) denotes the octets of the UTF-8 [RFC3629
> <http://tools.ietf.org/html/rfc3629>] representation
>
>    of STRING, where STRING is a sequence of zero or more Unicode
>
>    [UNICODE
> <http://tools.ietf.org/html/draft-ietf-jose-json-web-signature-41#ref-UNICODE>]
> characters.
>
>
>
>    ASCII(STRING) denotes the octets of the ASCII [RFC20
> <http://tools.ietf.org/html/rfc20>] representation
>
>    of STRING, where STRING is a sequence of zero or more ASCII
>
>    characters.
>
>
>
> This is unambiguous and has already been vetted by the IESG and SecDir, so
> I would use exactly this wording.
>
>
>
> OCTETS(STRING) is ambiguous, since for the same string there are many
> possible representations as octets, including ASCII, UTF-8, UTF-16, UTF-32,
> and EBCDIC.
>
>
>
>                                                                 -- Mike
>
>
>
> *From:* OAuth [mailto:oauth-bounces@ietf.org] *On Behalf Of *John Bradley
> *Sent:* Friday, January 30, 2015 11:33 AM
> *To:* Brian Campbell
> *Cc:* oauth; Naveen Agarwal
> *Subject:* Re: [OAUTH-WG] PKCE: SHA256(WAT?)
>
>
>
> 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 <bcampbell@pingidentity.com>
> 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 <sakimura@gmail.com> 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 <bcampbell@pingidentity.com>om>:
>
>  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) <nat@sakimura.org>
> 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 <bcampbell@pingidentity.com>
> 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
>
> nat@sakimura.org
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> --
>
> Nat Sakimura (=nat)
>
> Chairman, OpenID Foundation
> http://nat.sakimura.org/
> @_nat_en
>
>
>
>
>