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Created October 13, 2018 02:55
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ECDH Encrypted Key Exchange (Python 3.6+)
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes, padding
from cryptography.hazmat.primitives.asymmetric import ec
from cryptography.hazmat.primitives.kdf.hkdf import HKDF
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from secrets import token_bytes
class DiffieHellman:
def __init__(self):
self.diffieHellman = ec.generate_private_key(ec.SECP384R1(), default_backend())
self.public_key = self.diffieHellman.public_key()
self.IV = token_bytes(16)
def encrypt(self, public_key, secret):
shared_key = self.diffieHellman.exchange(ec.ECDH(), public_key)
derived_key = HKDF(
algorithm=hashes.SHA256(),
length=32,
salt=None,
info=None,
backend=default_backend()
).derive(shared_key)
aes = Cipher(algorithms.AES(derived_key), modes.CBC(self.IV), backend=default_backend())
encryptor = aes.encryptor()
padder = padding.PKCS7(128).padder()
padded_data = padder.update(secret.encode()) + padder.finalize()
return encryptor.update(padded_data) + encryptor.finalize()
def decrypt(self, public_key, secret, iv):
shared_key = self.diffieHellman.exchange(ec.ECDH(), public_key)
derived_key = HKDF(
algorithm=hashes.SHA256(),
length=32,
salt=None,
info=None,
backend=default_backend()
).derive(shared_key)
aes = Cipher(algorithms.AES(derived_key), modes.CBC(iv), backend=default_backend())
decryptor = aes.decryptor()
decrypted_data = decryptor.update(secret) + decryptor.finalize()
unpadder = padding.PKCS7(128).unpadder()
return unpadder.update(decrypted_data) + unpadder.finalize()
text = "Hello World!"
alice = DiffieHellman()
bob = DiffieHellman()
encrypted_message = bob.encrypt(alice.public_key, text)
print(encrypted_message)
decrypted_message = alice.decrypt(bob.public_key, encrypted_message, bob.IV)
print(decrypted_message)
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