[libmicrohttpd] [digest-auth]: bug in hash algorithm

[Andreas Wehrmann]

Hello!

I wrote a little testpage that I deliver using libmicrohttpd using 
digest authentication.
The testpage consists of four files (framed page + image file).
When I initially connected to the webserver via the browser it correctly 
challenged me
for my credentials. However, after entering the username and password 
the index file
got loaded but it happened that the browser then challenged me again for 
each
additional file to be loaded.
Since this is very annoying I tried increasing the nonce table size to 3000
(was default) but it was no good.
I then dug a little deeper and found out, that the hash algorithm to 
determine the index
for a given nonce always returned zero thus overwriting other nonces.
The offending line is at check_nonce_nc() in digestauth.c:313:

off = (off << 8) | (*np & (off >> 24));

whereas is should be:

off = (off << 8) | (*np ^ (off >> 24));

Since "off" is initialized with zero and an unsigned integer
a logical AND returns zero which is not right obviously.
After this fix, the server challenged me only once and I got "random" 
indices.
I found the problem in libmicrohttpd 0.9.5.

Best regards,
Andreas Wehrmann

--
Dipl.-Ing. (FH) Andreas Wehrmann
Software Development
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