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

John Bradley <ve7jtb@ve7jtb.com> Fri, 30 January 2015 20:47 UTC

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From: John Bradley <ve7jtb@ve7jtb.com>
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Date: Fri, 30 Jan 2015 17:47:36 -0300
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References: <CA+k3eCQHZJYJ3mMfdGTdO=S3VVQdU+qhjVz+QsEeobJokNSHEA@mail.gmail.com> <FD9F9F2A-8B32-4A26-95CC-59C8C465A202@sakimura.org> <CA+k3eCRn0xT+_fA0G3Q3OjjH9Lq-2AfC+Mv7Gq8bYnHqH5TFDw@mail.gmail.com> <CABzCy2CWnjmeBGT8hgQY-R9Z6u=UFM8AAvHDr1MV81kJXST9WQ@mail.gmail.com> <CA+k3eCTp3xyRuLdCtd3CK_uaACEOYvwYFb4DBs6Cy7UvVMX_ZA@mail.gmail.com> <EE51DE36-7566-4713-8AE3-9F815FA1EE77@ve7jtb.com> <4E1F6AAD24975D4BA5B1680429673943A2201928@TK5EX14MBXC291.redmond.corp.microsoft.com> <CA+k3eCQe9ZweUeoVD+U0H+fsLkbm73bD5ZT6r-wOxusgrq_1wg@mail.gmail.com>
To: Brian Campbell <bcampbell@pingidentity.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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OK try that one.

> On Jan 30, 2015, at 5:15 PM, Brian Campbell <bcampbell@pingidentity.com> wrote:
> 
> 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 <mailto:Michael.Jones@microsoft.com>> wrote:
> http://tools.ietf.org/html/draft-ietf-jose-json-web-signature-41#section-1.1 <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 <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 <mailto: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 <mailto: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 <mailto:bcampbell@pingidentity.com>>:
> 
> 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 <mailto: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.
> 
>  
> 
>  
> 
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> 
> On Jan 30, 2015, at 08:15, Brian Campbell <bcampbell@pingidentity.com <mailto: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 <https://tools.ietf.org/html/draft-ietf-oauth-spop-06#section-2>
>  
> 
> Nat Sakimura
> 
> nat@sakimura.org <mailto:nat@sakimura.org>
>  
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> 
> --
> 
> Nat Sakimura (=nat)
> 
> Chairman, OpenID Foundation
> http://nat.sakimura.org/ <http://nat.sakimura.org/>
> @_nat_en
> 
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>