Re: [rtcweb] JSEP fingerprint hash requirements

[Eric Rescorla <[e-mail]>]

On Tue, Oct 22, 2013 at 5:24 AM, Harald Alvestrand <[e-mail]>wrote:

> On 10/21/2013 06:38 PM, Martin Thomson wrote:
>
>> On 21 October 2013 07:21, Harald Alvestrand <[e-mail]> wrote:
>>
>>> When receiving browser supports both A and B, we could argue that they
>>> should be allowed to be different in the name of algorithm agility. But
>>> is
>>> there a real gain in security achieved by it?
>>>
>> Those are interesting cases, but they easily solved by saying
>> something like "MUST include/implement SHA-256".
>>
>
> Until SHA-512 comes along.
>
> If I don't support SHA-512, and the certificate says you have to use
> SHA-512 to verify the certificate, but I have a fingerprint using SHA-256,
> am I exposed to some attack I'd have been protected against if I understood
> SHA-512, or not?


I'm not quite sure I follow. If the certificate isn't being third-party
validated,
it's irrelevant what digest was used to sign the certificate.

-Ekr




>  I don't think that the hash used by the certificate is actually
>> relevant either.  Fingerprints are calculated, not observed or
>> extracted.
>>
>
> Well - they are extracted from SDP, and compared, which is a form of
> observation.... but you may be thinking of something else; I find that
> sentence hard to parse.
>
>