I really give up

[piter]

Nick,

OK it works! Thanks!
When masking with 32 bits set to "1" I was doing it with 0xffffffff instead
of long mask 0xffffffffL...

piter


Uzytkownik <QnickQm at alum.mit.edu> napisal w wiadomosci
news:slrnapm5mo.e5c.QnickQm at localhost.localdomain...
> In article <anf1bj$vu$1 at news.tpi.pl>, piter wrote:
> > Hey guys,
> >
> > I really give up! How to convert the following C function into python?
> >
> > //-----------------------------------------
> > unsigned int
> > make_hash(char *password, unsigned int seed)
> > {
> >     unsigned int x, y, z;
> >
> >     y = seed;
> >
> >     for (x = 0; *password; password++) {
> >         x = (x & 0xffffff00) | *password;
> >         y ^= x;
> >         y += x;
> >         x <<= 8;
> >         y ^= x;
> >         x <<= 8;
> >         y -= x;
> >         x <<= 8;
> >         y ^= x;
> >
> >         z = y & 0x1f;
> >         y = (y << z) | (y >> (32 - z));
> >     }
> >
> >     return y;
> > }
> >
> > //-----------------------------------------
> >
> > The obvious solution:
>  [...]
> > produces odd result due to python's signed arithmetic.
>
> One solution: use the low-order bytes of Python's long integers.
>
> def make_hash(password, seed):
>     y = long(seed)
>     x = 0L
>     for ch in password:
>         x = (x & 0xffffff00L) | ord(ch)
>         y ^= x
>         y += x
>         x <<= 8
>         y ^= x
>         x <<= 8
>         y -= x
>         x <<= 8
>         y ^= x
>         z = int(y & 0x1f)
>         y &= 0xffffffffL
>         y = ((y << z) | ((y >> (32- z))))
>
>     return y & 0xffffffffL
>
> Note however that this hashing algorithm is *not* secure.  A decent
desktop
> takes less than 4 minutes to try 2**32 passwords with a given seed.  Thus,
> assuming that the hashing algorithm works, I can should be able to find
> a password that hashes to any desired hash value for a given seed in that
> amount of time.  You may as well store the passwords in plaintext.
>
> Instead, may I suggest the sha module?
>
> Avoiding-roll-your-own-crypto-like-the-plague-ly y'rs,
>
> --
>  Nick Mathewson    <Q nick Q m at alum dot mit dot edu>
>                       Remove Q's to respond.  No spam.