From cd23f0af9e6c2a355463311cbe485577500b89a9 Mon Sep 17 00:00:00 2001
From: RubenCGomes <rlcg@ua.pt>
Date: Wed, 18 Dec 2024 15:53:28 +0000
Subject: [PATCH] diffie-hellman added (adaptation needed)

---
 delivery2/lib/diffie_hellman.py | 148 ++++++++++++++++++++++++++++++++
 1 file changed, 148 insertions(+)
 create mode 100644 delivery2/lib/diffie_hellman.py

diff --git a/delivery2/lib/diffie_hellman.py b/delivery2/lib/diffie_hellman.py
new file mode 100644
index 0000000..d231eb8
--- /dev/null
+++ b/delivery2/lib/diffie_hellman.py
@@ -0,0 +1,148 @@
+from cryptography.hazmat.primitives.asymmetric import dh
+from cryptography.hazmat.primitives import serialization, hashes
+from cryptography.hazmat.primitives.kdf.hkdf import HKDF
+from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
+from cryptography.hazmat.backends import default_backend
+
+import subprocess
+import os
+
+def generate_parameters(generator: int, key_size: int, backend=default_backend()):
+    """
+    Generate the parameters for the Diffie-Hellman key exchange
+    :param generator:
+    :param key_size:
+    :param backend:
+    :return:
+    """
+
+    if key_size < 512:
+        raise ValueError("Key size must be at least 512 bits")
+
+    if generator not in [2, 5]:
+        raise ValueError("Generator must be 2 or 5")
+
+    return dh.generate_parameters(generator, key_size, backend)
+
+
+def generate_key_pair(parameters: dh.DHParameters):
+    """
+    Generate a key pair for the Diffie-Hellman key exchange
+    :param parameters:
+    :return private_key, public_key:
+    """
+    private_key = parameters.generate_private_key()
+    return private_key, private_key.public_key()
+
+
+def derive_keys(private_key: dh.DHPrivateKey, peer_public_key: dh.DHPublicKey):
+    """
+    Derive the shared key from the private key and the peer's public key
+    :param private_key:
+    :param peer_public_key:
+    :return private_key, derived_key:
+    """
+    shared_key = private_key.exchange(peer_public_key)
+    derived_key = HKDF(
+        algorithm=hashes.SHA256(),
+        length=32,
+        salt=None,
+        info=b'handshake data',
+        backend=default_backend()
+    ).derive(shared_key)
+
+    print("Successfully derived key")
+    return derived_key
+
+
+# Encrypt content using the derived key
+def encrypt(content, key):
+    iv = os.urandom(16)
+    cipher = Cipher(algorithms.AES(key), modes.CFB(iv), backend=default_backend())
+    encryptor = cipher.encryptor()
+    ciphertext = iv + encryptor.update(content) + encryptor.finalize()
+    return ciphertext
+
+
+# Decrypt content using the derived key
+def decrypt(ciphertext, key):
+    iv = ciphertext[:16]
+    cipher = Cipher(algorithms.AES(key), modes.CFB(iv), backend=default_backend())
+    decryptor = cipher.decryptor()
+    plaintext = decryptor.update(ciphertext[16:]) + decryptor.finalize()
+    return plaintext
+
+
+def load_dh_public_key(file):
+    with open(file, 'rb') as key_file:
+        public_key = serialization.load_pem_public_key(
+            key_file.read(),
+        )
+    return public_key
+
+
+def load_dh_private_key(file, passwd=None):
+    if passwd is not None:
+        passwd = passwd.encode('utf-8')
+    try:
+        with open(file, 'rb') as key_file:
+            private_key = serialization.load_pem_private_key(
+                key_file.read(),
+                password=passwd,
+            )
+    except ValueError as e:
+        raise ValueError("Error: The password is not valid.") from e
+    return private_key
+
+
+def diffie_hellman():
+    # imagine that the agreement was done beforehand
+    generator = 2; key_size = 1024
+
+    parameters = generate_parameters(generator, key_size)
+
+    # generate keys for client and server
+    client_private_key, client_public_key = generate_key_pair(parameters)
+    server_private_key, server_public_key = generate_key_pair(parameters)
+
+    # derive keys
+    client_derived_key = derive_keys(client_private_key, server_public_key)
+    server_derived_key = derive_keys(server_private_key, client_public_key)
+
+    print("Client derived key: ", client_derived_key)
+    print("Server derived key: ", server_derived_key)
+
+
+    # write the keys to files
+    with open("client_private_key.pem", 'wb') as f:
+        f.write(client_private_key.private_bytes(encoding=serialization.Encoding.PEM,
+                                                 format=serialization.PrivateFormat.PKCS8,
+                                                 encryption_algorithm=serialization.NoEncryption()))
+
+    with open("server_private_key.pem", 'wb') as f:
+        f.write(server_private_key.private_bytes(encoding=serialization.Encoding.PEM,
+                                                 format=serialization.PrivateFormat.PKCS8,
+                                                 encryption_algorithm=serialization.NoEncryption()))
+
+    with open("client_derived_key.pem", 'wb') as f:
+        f.write(client_derived_key)
+
+    with open("server_derived_key.pem", 'wb') as f:
+        f.write(server_derived_key)
+
+    print(f"Client private key: \n\n{client_private_key}\nServer derived key: \n\n{server_derived_key}\n")
+    print(f"Server private key: \n\n{server_private_key}\nClient derived key: \n\n{client_derived_key}\n")
+
+    # test encryption
+
+    process = subprocess.Popen(f"dd if=/dev/zero of=file.txt bs=1024 count=1000", shell=True)
+
+    with open("file.txt", 'rb') as f:
+        data = f.read()
+
+    encrypted_data = encrypt(data, client_derived_key)
+
+    decrypted_data = decrypt(encrypted_data, server_derived_key)
+
+    if data == decrypted_data:
+        print("Encryption and decryption successful!")