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 <[email protected]> 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 <[email protected]>: > >> 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) <[email protected]> >> 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 <[email protected]> >>> 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 >>> [email protected] >>> >>> >>> >>> >>> >>> >> > > > -- > Nat Sakimura (=nat) > Chairman, OpenID Foundation > http://nat.sakimura.org/ > @_nat_en >
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