I have strings about 500 chars long and I'd like to encrypt them so that resulting string has the same length (or just slightly different). I need two way enryption and decryption using another "secret" string known to both sides. It doesn't need to be very secure, I prefer faster solutions.
2 Answers
From the post here: Encrypt string in Python
using http://code.google.com/p/keyczar/
crypter = Crypter.Read("/path/to/your/keys")
ciphertext = crypter.Encrypt("Secret message")
3 Comments
remy
I don't want to use keys, I want to use another string as a secret. Also seems like keyczar is no longer installable from pypi, not a good sign.
Erik Kaplun
copied from the dupe answer.
BoltClock
In future, please flag instead. The whole point of marking questions as duplicates is so we don't have to needlessly copy answers across questions.
If you want to preserve the length, then you want to use a stream cipher
Note that both parties need to know key (secret) and initialization vector (not secret, but must be unique).
It is not safe to reuse same key without a different IV, thus you'd need to communicate new IV across somehow, which effectively lengthens your encrypted package.
Furthermore, you really need to consider replay attacks -- what happens if someone intercepts your message and then sends it again and again.
Here's simple example for RC4, using pycrypto, no IV (RC4 doesn't support it):
import Crypto.Cipher.ARC4
plaintext = "x" * 13
c1 = Crypto.Cipher.ARC4.new(key="1")
ciphertext = c.encrypt(plaintext)
assert len(ciphertext) == len(plaintext)
c2 = Crypto.Cipher.ARC4.new(key="1")
result = c2.descrypt(ciphertext)
assert result == plaintext
data = "plaintext".encode("rot13").