Pure python crypto

[Paul Rubin]

Michael Gilfix <mgilfix at eecs.tufts.edu> writes:
>   Would anyone have any use for a pure python implementation of
> Blowfish? Or any other crypto algorithms for that matter.  As a matter
> of interest, I found myself implementing the blowfish module recently
> but was unsure if any audience would be interested. No C compiler
> is required, which is nice. Could use some testing though.

I wouldn't mind having it, but it wouldn't be THAT useful, as it
would be awfully slow, and I don't know of any important programs
to interoperate with that need Blowfish.

DES/3DES seems more important for interoperability purposes.  I coded
them in pure Python but made a mistake somewhere, so the test vectors
don't work correctly, and I never got around to debugging it.  I should
take a look at it again.

If you just want to encrypt in Python without custom C modules, after
a fair amount of experimentation the fastest way I found is to use the
SHA module in output feedback mode to generate a keystream from the
key and a random initialization string, and use the array module to
combine the keystream with the plaintext.  This works pretty well on
Un*x/Linux because the /dev/urandom device makes it easy to get the
initialization strings.  However, there's no good source of such
strings under Windows using the standard modules at the moment.