Python/ciphers/elgamal_key_generator.py

import os
import random
import sys

from . import cryptomath_module as cryptoMath
from . import rabin_miller as rabinMiller

min_primitive_root = 3


def main():
    print("Making key files...")
    makeKeyFiles("elgamal", 2048)
    print("Key files generation successful")


# I have written my code naively same as definition of primitive root
# however every time I run this program, memory exceeded...
# so I used 4.80 Algorithm in
# Handbook of Applied Cryptography(CRC Press, ISBN : 0-8493-8523-7, October 1996)
# and it seems to run nicely!
def primitiveRoot(p_val):
    print("Generating primitive root of p")
    while True:
        g = random.randrange(3, p_val)
        if pow(g, 2, p_val) == 1:
            continue
        if pow(g, p_val, p_val) == 1:
            continue
        return g


def generateKey(keySize):
    print("Generating prime p...")
    p = rabinMiller.generateLargePrime(keySize)  # select large prime number.
    e_1 = primitiveRoot(p)  # one primitive root on modulo p.
    d = random.randrange(3, p)  # private_key -> have to be greater than 2 for safety.
    e_2 = cryptoMath.findModInverse(pow(e_1, d, p), p)

    publicKey = (keySize, e_1, e_2, p)
    privateKey = (keySize, d)

    return publicKey, privateKey


def makeKeyFiles(name, keySize):
    if os.path.exists("%s_pubkey.txt" % name) or os.path.exists(
        "%s_privkey.txt" % name
    ):
        print("\nWARNING:")
        print(
            '"%s_pubkey.txt" or "%s_privkey.txt" already exists. \n'
            "Use a different name or delete these files and re-run this program."
            % (name, name)
        )
        sys.exit()

    publicKey, privateKey = generateKey(keySize)
    print("\nWriting public key to file %s_pubkey.txt..." % name)
    with open("%s_pubkey.txt" % name, "w") as fo:
        fo.write(
            "%d,%d,%d,%d" % (publicKey[0], publicKey[1], publicKey[2], publicKey[3])
        )

    print("Writing private key to file %s_privkey.txt..." % name)
    with open("%s_privkey.txt" % name, "w") as fo:
        fo.write("%d,%d" % (privateKey[0], privateKey[1]))


if __name__ == "__main__":
    main()