Re: CRAM-SHA1 support

[Lothar May]

Hi Simon,

thank you for your prompt reply!

2009/8/28 Simon Josefsson <address@hidden>:
[...]
> The SASL WG has just completed a last call on SCRAM-SHA1 which is the
> (long-awaited) replacement of both CRAM-MD5 and DIGEST-MD5.  I need to
> find time to implement it in GNU SASL.  If anyone wants to help with the
> implementation, that would be excellent.
>
> I'm aware that there are some libraries that support CRAM-SHA1, but it
> is not standardized.  It would be easier to implement than CRAM-MD5.
> However, because it is not standardized, and has some poor security
> properties as well (SCRAM solves them, that's why it took so long to
> complete) I'm not sure it is a good idea to support it.  Thoughts?
>

Do you mean this one: http://tools.ietf.org/html/draft-ietf-sasl-scram-05 ?
I've had a look at this also, and I like it, but it is quite complex.
I could not find any implementation of it. I've read completely
through it, even before having a look at gsasl, and considered
implementing it using gcrypt. There are several points I don't quite
understand, above all this part:

      AuthMessage     := client-first-message-bare + "," +
                         server-first-message + "," +
                         client-final-message-without-proof

These messages are defined, but I don't understand their definitions:

     client-final-message-without-proof =
                       channel-binding "," nonce [","
                       extensions]
     channel-binding = "c=" base64
                       ;; base64 encoding of cbind-input

What is "cbind-input"? I don't quite get it, this is probably because
I didn't yet read http://tools.ietf.org/html/rfc5056 about channel
binding. It's kind of complex. Same for this:

     client-first-message-bare =
                       [reserved-mext ","]
                       username "," nonce ["," extensions]

     reserved-mext  = "m=" 1*(value-char)
                       ;; Reserved for signalling mandatory extensions.
                       ;; The exact syntax will be defined in
                       ;; the future.

There is an optional argument at the beginning. So the username
"m=..." is not valid? Or do you have to count how many commas there
are? This seems very strange. I have more questions like this, which
tells me that I'm probably not the right one to implement this... :-/

Regards,
Lothar