makePublicPrivateKeys.py

#! python3

import random, sys, os, primeNum, cryptomath


def main():
    print("Making key files...")
    makeKeyFiles("my", 1024)
    print("Key files made.")


def generateKey(keySize):
    p = 0
    q = 0
    # Step 1: Create two prime numbers, p and q. Calculate n = p * q.
    print("Generating p & q primes...")
    while p == q:
        p = primeNum.generateLargePrime(keySize)
        q = primeNum.generateLargePrime(keySize)
    n = p * q
    # Step 2: Create a number e that is relatively prime to (p-1)*(q-1).
    print("Generating e that is relatively prime to (p-1)*(q-1)...")
    while True:
        e = random.randrange(2 ** (keySize - 1), 2 ** (keySize))
        if cryptomath.gcd(e, (p - 1) * (q - 1)) == 1:
            break
    # Step 3: Calculate d, the mod inverse of e.
    print("Calculating d that is mod inverse of e...")
    d = cryptomath.findModInverse(e, (p - 1) * (q - 1))

    publicKey = (n, e)
    privateKey = (n, d)

    print("Public key:", publicKey)
    print("Private key:", privateKey)

    return (publicKey, privateKey)


def makeKeyFiles(name, keySize):
    if os.path.exists("%s_pubkey.txt" % (name)) or os.path.exists(
        "%s_privkey.txt" % (name)
    ):
        sys.exit(
            "WARNING: The file %s_pubkey.txt or %s_privkey.txt already exists! Use a different name or delete these files and re-run this program."
            % (name, name)
        )
    publicKey, privateKey = generateKey(keySize)

    print()
    print(
        "The public key is a %s and a %s digit number."
        % (len(str(publicKey[0])), len(str(publicKey[1])))
    )
    print("Writing public key to file %s_pubkey.txt..." % (name))
    fo = open("%s_pubkey.txt" % (name), "w")
    fo.write("%s,%s,%s" % (keySize, publicKey[0], publicKey[1]))
    fo.close()

    print()
    print(
        "The private key is a %s and a %s digit number."
        % (len(str(privateKey[0])), len(str(privateKey[1])))
    )
    print("Writing private key to file %s_privkey.txt..." % (name))
    fo = open("%s_privkey.txt" % (name), "w")
    fo.write("%s,%s,%s" % (keySize, privateKey[0], privateKey[1]))
    fo.close()


if __name__ == "__main__":
    main()