Implementing-cryptography-using-python

270 Chapter 9 ■ Mastering Cryptography Using Python
if data == b'removeDH':
useDH = False
return 20
return 1
Creating the Diffie-Hellman Class File
There are many cryptographic libraries that will handle the Diffie-Hellman
exchange for you, and the DH primes listed in this section are a bit brutal to
type; the code listed in this section is presented more to help you understand
how the protocol works. This code, like all of the code in this book, is available
on the book’s website. This section is mostly for students who need to understand
how to generate the Diffie-Hellman exchange in other languages that
may not have libraries for it or for those of you in academia:
import hashlib
from binascii import hexlify
try:
#Preferably using urandom (more secure)
import os
random_function = os.urandom
random_provider = "OS random"
except (AttributeError, ImportError):
import ssl
random_function = ssl.RAND_bytes
random_provider = "Python SSL"
class DiffieHellman():
"""
Using standard primes from RFC 3526 MODP Groups 17 and 18.
Both are sufficient to generate AES 256 keys with a 540+ bit
exponent.
https://datatracker.ietf.org/doc/rfc3526/
"""
def __init__ (self, generator = 2, group = 17, keyLength=2048):
"""
Generate the public and private keys
"""
#Length in bits
min_keyLength = 1024
default_keyLength = 2024
default_generator = 2
valid_generators = [2, 3, 7] #Must be primes