Private/Public Encryption in Python with Standard Library

Question

Is there a module that has my searching has been unable to discover that would allow writing code like the following? The reason for wanting to write code like this is unimportant. All I am after is some code that has a simple API to generate public and private byte keys and to easily encode and decode data with those keys.

import module, os  method, bits, data = 'RSA', 1024, os.urandom(1024) public, private = module.generate_keys(method, bits)  assert isinstance(public, bytes) and isinstance(private, bytes) assert module.decode(module.encode(data, private), public) == data assert module.decode(module.encode(data, public), private) == data 

Most of what appears to be available requires downloading a package and only runs on Python 2.x. It is also quite common to find libraries that work with PEM files or other types of certificates. I would like to avoid having to deal with such files, to generate public and private keys on the fly, and quickly work with data in memory.

Answer 1

Public key encryption is not in the standard library. There are some third party libraries on PyPi for it though:

• PyCrypto
• RSA Python

If you're interested in the math behind it, Python makes it easy to experiment:

code = pow(msg, 65537, 5551201688147)               # encode using a public key plaintext = pow(code, 109182490673, 5551201688147)  # decode using a private key 

The key generation is a little more involved. Here is a simplified example of how to do key generation in-memory using urandom as the source of entropy. The code runs under both Py2.6 and Py3.x:

import random  def gen_prime(N=10**8, bases=range(2,20000)):     # XXX replace with a more sophisticated algorithm     p = 1     while any(pow(base, p-1, p) != 1 for base in bases):         p = random.SystemRandom().randrange(N)     return p  def multinv(modulus, value):     '''Multiplicative inverse in a given modulus          >>> multinv(191, 138)         18         >>> 18 * 138 % 191         1      '''     # http://en.wikipedia.org/wiki/Extended_Euclidean_algorithm     x, lastx = 0, 1     a, b = modulus, value     while b:         a, q, b = b, a // b, a % b         x, lastx = lastx - q * x, x     result = (1 - lastx * modulus) // value     return result + modulus if result < 0 else result  def keygen(N):     '''Generate public and private keys from primes up to N.          >>> pubkey, privkey = keygen(2**64)         >>> msg = 123456789012345         >>> coded = pow(msg, 65537, pubkey)         >>> plain = pow(coded, privkey, pubkey)         >>> assert msg == plain      '''     # http://en.wikipedia.org/wiki/RSA     prime1 = gen_prime(N)     prime2 = gen_prime(N)     totient = (prime1 - 1) * (prime2 - 1)     return prime1 * prime2, multinv(totient, 65537) 

Answer 2

PyCrypto works on Python 3 as of 2.4.1.