Python and RSA

There are many Python toolkits for crypto, so I hope I've done the best choice (at least for now). This is a simple utility class for managing RSA keys, a sort of wrappera to the m2crypto class.

import M2Crypto

class RSA (object):
def __init__ (self, bits=1024, padding=M2Crypto.RSA.pkcs1_padding, exp=65537):
    self.bits = bits
    self.padding = padding
    self.exp = exp
    self.rsa = None

def generate (self):
    self.rsa = M2Crypto.RSA.gen_key(
        self.bits, self.exp, lambda x: None)

def encrypt (self, s):
    c = ""
    bytes = self.bits/8-11
    for i in range(0, len(s), bytes):
        c += self.rsa.public_encrypt (s[i:i+bytes], self.padding)
    return c

def sign (self, s, algo="sha1"):
    dgst = M2Crypto.EVP.MessageDigest (algo)
    dgst.update (s)
    return self.rsa.sign (dgst.digest (), algo)

def verify (self, s, sign, algo="sha1"):
    dgst = M2Crypto.EVP.MessageDigest (algo)
    dgst.update (s)
    try:
        self.rsa.verify (dgst.digest (), sign, algo)
    except:
        return False
    return True

def decrypt (self, c):
    s = ""
    bytes = self.bits/8
    for i in range(0, len(c), bytes):
        s += self.rsa.private_decrypt (c[i:i+bytes], self.padding)
    return s

Example usage:

rsa = RSA ()
rsa.generate () # generate key pair
s = "a"*2000 # test data
edata = rsa.encrypt (s)
sign = rsa.sign (s)

ddata = rsa.decrypt (edata)
assert rsa.verify (ddata, sign) == True