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

Brian Campbell <bcampbell@pingidentity.com> Fri, 30 January 2015 13:52 UTC

Return-Path: <bcampbell@pingidentity.com>
X-Original-To: oauth@ietfa.amsl.com
Delivered-To: oauth@ietfa.amsl.com
Received: from localhost (ietfa.amsl.com [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id CE95C1A0373 for <oauth@ietfa.amsl.com>; Fri, 30 Jan 2015 05:52:15 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -3.578
X-Spam-Level:
X-Spam-Status: No, score=-3.578 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, FM_FORGED_GMAIL=0.622, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_MED=-2.3, SPF_PASS=-0.001] autolearn=ham
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id zA0xJcUn2VfN for <oauth@ietfa.amsl.com>; Fri, 30 Jan 2015 05:52:13 -0800 (PST)
Received: from na3sys009aog131.obsmtp.com (na3sys009aog131.obsmtp.com [74.125.149.247]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 193A21A01F2 for <oauth@ietf.org>; Fri, 30 Jan 2015 05:52:12 -0800 (PST)
Received: from mail-ie0-f174.google.com ([209.85.223.174]) (using TLSv1) by na3sys009aob131.postini.com ([74.125.148.12]) with SMTP ID DSNKVMuMjHlYN8sdiumNN4PGMxgnW5z0Epe1@postini.com; Fri, 30 Jan 2015 05:52:13 PST
Received: by mail-ie0-f174.google.com with SMTP id vy18so3439068iec.5 for <oauth@ietf.org>; Fri, 30 Jan 2015 05:52:12 -0800 (PST)
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc:content-type; bh=JOySFO0xRe3U63hYm4udsUTtUPVpzX71CGd/QMcB5CM=; b=i12+NZYNsn8szLB686W0Kg/scIZ1lZIEspWDkkumHz4Ve5YjF9oQhwCYUkvwt10xeU wSbXTxXR0517eQGC6nky240G9eTBjjCInEOvmZLVDHjia/qiSSkJ3SxRKyhKbjDRNeAC ASKScKi9VyMZbK33rojYRwfeiSM/20gB0XCtRamCrYWh/ixzZeMuR5llqZyBLYKYlUtf YJ/otXI+f7dO5PX+BpyWiJXcpDu6Z8VwQAUOkVw7VJir6BVG2ttiVS5apOKnb4qe9K22 fxc+i2rLdCZfaHdXMTRKkYb01bw9TCn1O2rIS2PKym91EkfkpV3GMw7SWQkbM/rFa3wY SW9g==
X-Gm-Message-State: ALoCoQm/MqLHugamaT2pmLR3E9/Mfj/3jbnvzIDIKsC5ctsZE+NHRiBFtjUtyBf5QnaFlfPSkrFgh4+uk4HCWbvzDSjlajKsAeFVcjjkt1ZcTIV9xsdlG4oPRKbf0oBAatS8nkKKjf1O
X-Received: by 10.107.149.203 with SMTP id x194mr7511361iod.12.1422625932204; Fri, 30 Jan 2015 05:52:12 -0800 (PST)
X-Received: by 10.107.149.203 with SMTP id x194mr7511349iod.12.1422625932088; Fri, 30 Jan 2015 05:52:12 -0800 (PST)
MIME-Version: 1.0
Received: by 10.64.33.75 with HTTP; Fri, 30 Jan 2015 05:51:41 -0800 (PST)
In-Reply-To: <FD9F9F2A-8B32-4A26-95CC-59C8C465A202@sakimura.org>
References: <CA+k3eCQHZJYJ3mMfdGTdO=S3VVQdU+qhjVz+QsEeobJokNSHEA@mail.gmail.com> <FD9F9F2A-8B32-4A26-95CC-59C8C465A202@sakimura.org>
From: Brian Campbell <bcampbell@pingidentity.com>
Date: Fri, 30 Jan 2015 06:51:41 -0700
Message-ID: <CA+k3eCRn0xT+_fA0G3Q3OjjH9Lq-2AfC+Mv7Gq8bYnHqH5TFDw@mail.gmail.com>
To: Nat Sakimura <sakimura@gmail.com>
Content-Type: multipart/alternative; boundary=001a1140eed654db51050ddee979
Archived-At: <http://mailarchive.ietf.org/arch/msg/oauth/dFq4kHDDguRLmQf4ptnadc0Psug>
Cc: oauth <oauth@ietf.org>, Naveen Agarwal <naa@google.com>
Subject: Re: [OAUTH-WG] PKCE: SHA256(WAT?)
X-BeenThere: oauth@ietf.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: OAUTH WG <oauth.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/oauth>, <mailto:oauth-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/oauth/>
List-Post: <mailto:oauth@ietf.org>
List-Help: <mailto:oauth-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/oauth>, <mailto:oauth-request@ietf.org?subject=subscribe>
X-List-Received-Date: Fri, 30 Jan 2015 13:52:16 -0000

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
>
>
>
>
>
>