Implementing-cryptography-using-python

258 Chapter 9 ■ Mastering Cryptography Using Python
Modifying the Helper File
The helper file will be growing quite a bit now. In addition to using it to create
the private and public key files, we also use it for reading the key files and
performing our encryption and decryption process. You’ve seen code examples
of this in a number of chapters, but if you would like to review the topic again,
check out Chapter 5.
PyCrypto is being used in this example to expose the PKCS1_OAEP module.
The only difference between the encryption and decryption methods is the use
of specific keys:
# Chat Encryption Helper - ch9_crypto_chat.py
import os, base64, json
from Crypto.Cipher import PKCS1_OAEP, AES
from Crypto.PublicKey import RSA, ECC
from binascii import hexlify, unhexlify
from base64 import b64encode, b64decode
# encryption method used by all calls
def encrypt(message, usePKI, useDH, dhSecret):
if usePKI == True:
message = encrypt_rsa(message)
return message
# decryption method used by all calls
def ch9_decrypt(message, usePKI, useDH, dhSecret):
if usePKI == True:
message = ch9_decrypt_rsa(message)
return message
# generate RSA certs
def gen_rsa_certs():
#ch8_Generate_RSA_Certs.py
from Crypto.PublicKey import RSA
#Generate a public/private key pair using 4096 bits key length (512
bytes)
new_key = RSA.generate(4096, e=65537)
#The private key in PEM format
private_key = new_key.exportKey("PEM")
#The public key in PEM Format
public_key = new_key.publickey().exportKey("PEM")
fd = open("client_private_key.pem", "wb")
fd.write(private_key)
fd.close()