I don't think a null string means there's a null pointer -
It just means that the string is empty.
What I didn't realise was that you can put an empty
string (aka null string) into the MD5 algorithm
and still yield a valid result.
The RFC for MD5 message digest is here:
http://www.faqs.org/rfcs/rfc1321.html
And near the bottom it says:
> MD5 test suite:
> MD5 ("") = d41d8cd98f00b204e9800998ecf8427e
So, when "ContentLength" is zero, then:
H(entity-body) = H("") = d41d8cd98f00b204e9800998ecf8427e
Anyway, thanks to everyone for all the help.
> -----Original Message-----
> From: Jonathan Rosenberg [mailto:[EMAIL PROTECTED]]
> Sent: 07 March 2001 01:47
> To: 'PD20 Frank Lin'; '[EMAIL PROTECTED]'
> Subject: RE: [Sip-implementors] REGISTRATION with authorization.
> H(entity -body)?
>
>
>
>
>
>
> > -----Original Message-----
> > From: PD20 Frank Lin [mailto:[EMAIL PROTECTED]]
> > Sent: Tuesday, March 06, 2001 6:35 PM
> > To: '[EMAIL PROTECTED]'
> > Subject: FW: [Sip-implementors] REGISTRATION with authorization.
> > H(entity -body)?
> >
> >
> > We were tackling the same question and I remember doing some
> > searches on the
> > web for discussions on authentication (not specifically for
> > SIP). It appears
> > that you just use NULL for the entity-body. Here's the URL to that
> > discussion:
> >
> > http://www.hp.co.uk/people/ange/archives/http-wg-archive/0547.html
> >
> > Frank
>
> Hmm. This list post says:
>
> Dave Kristol wrote:
> >>
> >> On Thu, 9 Apr 1998, Dave Kristol wrote:
> >> > [...]
> >> > Now, for qop="auth-int", the client must include
> H(entity-body) in
> >> > the calculation of A2. But there is no entity-body.
> Does the
> >> > client use the null string when it calculates A2?
> >>
> >> It uses the hash of the null string, actually.
> >
> >I think it would be wise to add an explicit statement to
> that effect to
> >the draft.
>
> Hash of the null string? Isn't that what we call NullPointerException?
>
> -Jonathan R.
>
> ---
> Jonathan D. Rosenberg 72 Eagle Rock Ave.
> Chief Scientist First Floor
> dynamicsoft East Hanover, NJ 07936
> [EMAIL PROTECTED] FAX: (973) 952-5050
> http://www.cs.columbia.edu/~jdrosen PHONE: (973) 952-5000
> http://www.dynamicsoft.com
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