XSalsa20-Poly1305 Encryption Example

encryption.py

import nacl.utils
from nacl.public import PrivateKey, Box
from nacl.secret import SecretBox
import nacl.bindings

def generate_keypair():
    private_key = PrivateKey.generate()
    public_key = private_key.public_key
    return private_key, public_key

def perform_key_exchange(private_key, other_public_key):
    shared_key = Box(private_key, other_public_key).shared_key()
    return shared_key

def derive_key_hsalsa20(shared_key, nonce):
    derived_key = nacl.bindings.crypto_core_hsalsa20(shared_key, nonce)
    return derived_key

def encrypt_message(key, message):
    # Create a SecretBox with our key
    box = SecretBox(key)
    # Encrypt the message
    encrypted = box.encrypt(message.encode())
    return encrypted

def decrypt_message(key, encrypted):
    # Create a SecretBox with our key
    box = SecretBox(key)
    # Decrypt the message
    decrypted = box.decrypt(encrypted)
    return decrypted.decode()

# Example usage
if __name__ == "__main__":
    # Generate keypairs for Alice and Bob
    alice_private, alice_public = generate_keypair()
    bob_private, bob_public = generate_keypair()
    
    # Perform key exchange
    alice_shared = perform_key_exchange(alice_private, bob_public)
    bob_shared = perform_key_exchange(bob_private, alice_public)
    
    # Generate a nonce for key derivation
    kdf_nonce = nacl.utils.random(16)
    
    # Derive keys using HSalsa20
    alice_derived_key = derive_key_hsalsa20(alice_shared, kdf_nonce)
    bob_derived_key = derive_key_hsalsa20(bob_shared, kdf_nonce)
    
    # Alice encrypts a message
    message = "Hello, Bob! This is a secret message."
    encrypted = encrypt_message(alice_derived_key, message)
    
    # Bob decrypts the message
    decrypted = decrypt_message(bob_derived_key, encrypted)
    
    print("Original message:", message)
    print("Encrypted message:", encrypted.hex())
    print("Decrypted message:", decrypted)
    print("Decryption successful:", message == decrypted)