what python package for rsa algorithm

Question

looking to do RSA encryption on a short string in python. This is for a piece of user data that I want to store without staff (incl myself) being able to see it. The private key will be on a thumbdrive in my safety deposit box for when we get subpoenaed.

my question: is there a 'probably correct' python package for asymmetric-key RSA? Will I be safer to use a C library (if so which one).

Answer 1

Encryption of short strings with RSA can be problematic. There are certain pieces of data you can encrypt with RSA that reveal details about your private key. In your case it will probably be fine since it will be obscure enough your staff won't figure it out. But in the general case, with a knowledgeable and/or well-funded adversary, you do not want to use RSA to directly encrypt data if you want that data to be kept secret.

I would recommend just using gnupg instead. It's solved all those problems for you.

Answer 2

PyCrypto

Answer 3

pycryptopp

Answer 4

def gcd (a, b):
    "Compute GCD of two numbers"

    if b == 0: return a
    else: return gcd(b, a % b)

def multiplicative_inverse(a, b):
    """ Find multiplicative inverse of a modulo b (a > b)
        using Extended Euclidean Algorithm """

    origA = a
    X = 0
    prevX = 1
    Y = 1
    prevY = 0

    while b != 0:

        temp = b
        quotient = a/b
        b = a % b
        a = temp

        temp = X
        a = prevX - quotient * X
        prevX = temp

        temp = Y
        Y = prevY - quotient * Y
        prevY = temp

    return origA + prevY

def generateRSAKeys(p, q):
    "Generate RSA Public and Private Keys from prime numbers p & q"

    n = p * q
    m = (p - 1) * (q - 1)

    # Generate a number e so that gcd(n, e) = 1, start with e = 3
    e = 3

    while 1:

        if gcd(m, e) == 1: break
        else: e = e + 2

    d = multiplicative_inverse(m, e)   

    # Return a tuple of public and private keys 
    return ((n,e), (n,d))           

if __name__ == "__main__":

    print "RSA Encryption algorithm...."
    p = long(raw_input("Enter the value of p (prime number):"))
    q = long(raw_input("Enter the value of q (prime number):"))

    print "Generating public and private keys...."
    (publickey, privatekey) = generateRSAKeys(p, q)

    print "Public Key (n, e) =", publickey
    print "Private Key (n, d) =", privatekey

    n, e = publickey
    n, d = privatekey

    input_num = long(raw_input("Enter a number to be encrypted:"))
    encrypted_num = (input_num ** e) % n
    print "Encrypted number using public key =", encrypted_num
    decrypted_num = encrypted_num ** d % n
    print "Decrypted (Original) number using private key =", decrypted_num