TP03 pbenc_aes_ctr_hmac in python

TPs/TP03/py/pbenc_aes_ctr_hmac.py

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+#!/usr/bin/env python3
+
+from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
+from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC
+from cryptography.hazmat.primitives import hashes
+from cryptography.hazmat.primitives import hmac
+import os
+import argparse
+
+
+
+def encrypt(input_file, password):
+    inp = open(input_file,"rb")
+    out = open(f"{input_file}.enc","wb")
+
+    plaintext = inp.read()
+    print(f"plaintext len : {len(plaintext)}")
+
+
+    # Derive the key from the password using PBKDF2
+    salt = os.urandom(16)
+    kdf = PBKDF2HMAC(
+        algorithm=hashes.SHA256(),
+        length=64,
+        salt=salt,
+        iterations=100000
+    )
+    # FIX: key length must be 32 bytes
+    derived_key = kdf.derive(password.encode('utf-8'))
+
+    key = derived_key[:32]
+    hmac_key = derived_key[32:]
+
+    iv = os.urandom(16)
+
+    cipher = Cipher(algorithms.AES(key),modes.CTR(iv))
+    encryptor = cipher.encryptor()
+    ciphertext = encryptor.update(plaintext)
+    
+    ciphertext = salt + iv + ciphertext
+
+    print(f"plaintext len : {len(plaintext)}")
+    print(f"ciphertext len : {len(ciphertext)}")
+    print(f"iv len : {len(iv)}")    
+
+    h = hmac.HMAC(hmac_key,hashes.SHA256())
+    h.update(ciphertext)
+    tag = h.finalize()
+    ciphertext = ciphertext + tag
+
+    out.write(ciphertext)
+
+    inp.close()
+    out.close()
+
+def decrypt(input_file,password):
+    inp = open(f"{input_file}","rb")
+    out = open(f"{input_file}.dec","wb")
+
+    input_bytes = inp.read()
+    salt = input_bytes[:16]
+    iv = input_bytes[16:32]
+    ciphertext = input_bytes[32:-32]
+    tag = input_bytes[-32:]
+
+    kdf = PBKDF2HMAC(
+        algorithm=hashes.SHA256(),
+        length=64,
+        salt=salt,
+        iterations=100000
+    )
+
+    print(f"plaintext len : {len(ciphertext)}")
+    print(f"iv len : {len(iv)}")
+    print(f"salt len : {len(salt)}")
+
+    derived_key = kdf.derive(password.encode('utf-8'))
+    hmac_key = derived_key[32:]
+    key = derived_key[:32]
+
+    # FIX: block size for aes must be 16 bytes
+    # plaintext needs padding
+    cipher = Cipher(algorithms.AES(key),modes.CTR(iv))
+    decryptor = cipher.decryptor()
+    plaintext = decryptor.update(ciphertext)
+
+    h = hmac.HMAC(hmac_key,hashes.SHA256())
+    h.update(salt + iv + ciphertext)
+    if (h.finalize() != tag):
+        print("Error: HMAC verification failed")
+        return
+
+
+    out.write(plaintext)
+
+    inp.close()
+    out.close()
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Program to perform operations using AES cipher on files",
+    )
+
+    subparsers = parser.add_subparsers(dest="operation", help="Operation to perform")
+
+    # Encrypt subcommand
+    enc_parser = subparsers.add_parser("enc", help="Encrypt a file")
+    enc_parser.add_argument("fich", help="File to be encrypted")
+    enc_parser.add_argument("password", help="Pass-phrase to derive the key")
+
+    # Decrypt subcommand
+    dec_parser = subparsers.add_parser("dec", help="Decrypt a file")
+    dec_parser.add_argument("fich", help="File to be decrypted")
+    dec_parser.add_argument("password", help="Pass-phrase to derive the key")
+
+    args = parser.parse_args()
+    match args.operation:
+        case "enc":
+            input_file = args.fich
+            password = args.password
+            encrypt(input_file,password)
+        case "dec":
+            input_file = args.fich
+            password = args.password
+            decrypt(input_file,password)
+
+if __name__ == "__main__":
+    main()

TPs/TP03/py/plaintext.txt

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+not very safe

TPs/TP03/py/plaintext.txt.enc.dec

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+not very safe