"""Public Key Generator
Implements series of functions capable of creating a `textbook RSA`_ public/private keypair and saves them to text
files.
Note:
* https://www.nostarch.com/crackingcodes/ (BSD Licensed)
* 'Textbook/Plain' RSA keys are not secure and should not be used to encrypt sensitive data.
.. _textbook RSA:
https://en.wikipedia.org/wiki/RSA_(cryptosystem)#Attacks_against_plain_RSA
"""
import random, sys, os
from pythontutorials.books.CrackingCodesWithPython.Chapter13.cryptomath import gcd, findModInverse
from pythontutorials.books.CrackingCodesWithPython.Chapter22.primeNum import generateLargePrime
[docs]def main():
# Create a public/private keypair with 1024-bit keys:
print('Making key files...')
makeKeyFiles('al_sweigart', 1024)
print('Key files made.')
[docs]def generateKey(keySize: int) -> tuple:
"""Generate public/private keypair
Creates public/private keys keySize bits in size.
Args:
keySize: Bit size to make public/private keys.
Returns:
Tuples containing the public and private keypair split into their two halves.
"""
p = 0
q = 0
# Step 1: Create two prime numbers, p and q. Calculate n = p * q:
print('Generating p prime...')
while p == q:
p = generateLargePrime(keySize)
q = 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:
# Keep trying random numbers for e until one is valid:
e = random.randrange(2 ** (keySize - 1), 2 ** keySize)
if 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 = findModInverse(e, (p - 1) * (q - 1))
publicKey = (n, e)
privateKey = (n, d)
print('Public key:', publicKey)
print('Private key:', privateKey)
return publicKey, privateKey
[docs]def makeKeyFiles(name: str, keySize: int) -> None:
"""Make key files
Creates two files 'x_pubkey.txt' and 'x_privkey.txt' (where x
is the value in name) with the n,e and d,e integers written in
them, delimited by a comma.
Args:
name: Name to append to public/private key files.
keySize: Bit size to make public/private keys.
Returns:
None. Key files are created in current working directory.
Note:
* Checks if key files with given name already exist and exits with warning if so.
"""
# Our safety check will prevent us from overwriting our old key files:
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 rerun 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 makePublicPrivateKeys.py is run (instead of imported as a module),
# call the main() function:
if __name__ == '__main__':
main()