Encryption with Python?

[Paul Rubin]

"Anthra Norell" <anthra.norell at tiscalinet.ch> writes:
> I rolled my own for relatively short sequences, like passwords. The
> key is an integer. To decrypt use the negative encryption key. I
> consider the encryption unbreakable, as it is indistinguishable from
> a random sequence.

You're using the built-in random module which is designed to provide
only statistical randomness and not cryptographic security.  It should
not be used for encryption.  The math paper describing the function is
quite clear about that.  There is a lot of subtlety to this stuff and
it's easy to make mistakes even if you know what you're doing.  Even
using well-tested block ciphers (various people mentioned DES, AES,
and Blowfish modules) it's easy to make mistakes in choosing operation
modes, thinking you don't need authentication when you really do,
etc., etc.  The book "Practical Cryptography" by Bruce Schneier and
Niels Ferguson is worth looking at if you want to see what you're
getting yourself into.

I hate to come across as plugging my own stuff too much, but

    http://www.nightsong.com/phr/crypto/p3.py

is designed to take care of most of the tricky issues for you while
still having a very simple interface, and also be reasonably fast
(much faster for large messages than any of the pure Python block
cipher modules).  Just use p3_encrypt(plain) to encrypt and
p3_decrypt(cipher) to decrypt.  The main penalty you pay is that the
ciphertext is a couple dozen bytes longer than the plaintext.  There
are cryptographically important reasons for that; don't try to escape
it without knowing exactly what's going on.