#### Rsa Key Generator

I
import os
import random
import sys

from maths.greatest_common_divisor import gcd_by_iterative

from . import cryptomath_module, rabin_miller

def main() -> None:
print("Making key files...")
make_key_files("rsa", 1024)
print("Key files generation successful.")

def generate_key(key_size: int) -> tuple[tuple[int, int], tuple[int, int]]:
"""
>>> random.seed(0) # for repeatability
>>> public_key, private_key = generate_key(8)
>>> public_key
(26569, 239)
>>> private_key
(26569, 2855)
"""
p = rabin_miller.generate_large_prime(key_size)
q = rabin_miller.generate_large_prime(key_size)
n = p * q

# Generate e that is relatively prime to (p - 1) * (q - 1)
while True:
e = random.randrange(2 ** (key_size - 1), 2 ** (key_size))
if gcd_by_iterative(e, (p - 1) * (q - 1)) == 1:
break

# Calculate d that is mod inverse of e
d = cryptomath_module.find_mod_inverse(e, (p - 1) * (q - 1))

public_key = (n, e)
private_key = (n, d)
return (public_key, private_key)

def make_key_files(name: str, key_size: int) -> None:
if os.path.exists(f"{name}_pubkey.txt") or os.path.exists(f"{name}_privkey.txt"):
print("\nWARNING:")
print(
f'"{name}_pubkey.txt" or "{name}_privkey.txt" already exists. \n'
"Use a different name or delete these files and re-run this program."
)
sys.exit()

public_key, private_key = generate_key(key_size)
print(f"\nWriting public key to file {name}_pubkey.txt...")
with open(f"{name}_pubkey.txt", "w") as out_file:
out_file.write(f"{key_size},{public_key[0]},{public_key[1]}")

print(f"Writing private key to file {name}_privkey.txt...")
with open(f"{name}_privkey.txt", "w") as out_file:
out_file.write(f"{key_size},{private_key[0]},{private_key[1]}")

if __name__ == "__main__":
main()