Create a file encryption tool

Here’s a simple file encryption tool written in Python using the cryptography library. It allows you to encrypt and decrypt files securely with a password-derived key.

python
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from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.backends import default_backend
from cryptography.fernet import Fernet
import base64
import os

def derive_key(password: bytes, salt: bytes) -> bytes:
    # Derive a secret key from a password and salt using PBKDF2 HMAC SHA256
    kdf = PBKDF2HMAC(
        algorithm=hashes.SHA256(),
        length=32,
        salt=salt,
        iterations=100_000,
        backend=default_backend()
    )
    return base64.urlsafe_b64encode(kdf.derive(password))

def encrypt_file(filepath: str, password: str):
    salt = os.urandom(16)  # Random salt for key derivation
    key = derive_key(password.encode(), salt)
    fernet = Fernet(key)

    with open(filepath, 'rb') as f:
        data = f.read()

    encrypted = fernet.encrypt(data)

    # Save salt + encrypted data to file
    with open(filepath + '.enc', 'wb') as f:
        f.write(salt + encrypted)

    print(f"File encrypted successfully: {filepath}.enc")

def decrypt_file(encrypted_filepath: str, password: str):
    with open(encrypted_filepath, 'rb') as f:
        salt = f.read(16)  # First 16 bytes are the salt
        encrypted_data = f.read()

    key = derive_key(password.encode(), salt)
    fernet = Fernet(key)

    try:
        decrypted = fernet.decrypt(encrypted_data)
    except Exception as e:
        print("Decryption failed. Incorrect password or corrupted file.")
        return

    # Save decrypted file without the .enc extension
    original_filepath = encrypted_filepath.rsplit('.enc', 1)[0]
    with open(original_filepath, 'wb') as f:
        f.write(decrypted)

    print(f"File decrypted successfully: {original_filepath}")

if __name__ == "__main__":
    import argparse

    parser = argparse.ArgumentParser(description="Simple file encryption tool.")
    parser.add_argument('mode', choices=['encrypt', 'decrypt'], help="Choose to encrypt or decrypt")
    parser.add_argument('file', help="File to encrypt or decrypt")
    parser.add_argument('password', help="Password for encryption/decryption")

    args = parser.parse_args()

    if args.mode == 'encrypt':
        encrypt_file(args.file, args.password)
    else:
        decrypt_file(args.file, args.password)

Usage

• Encrypt:
  python encrypt_tool.py encrypt filename.txt yourpassword

• Decrypt:
  python encrypt_tool.py decrypt filename.txt.enc yourpassword

This uses a strong password-based key derivation (PBKDF2) with a random salt stored alongside the encrypted file for security, and symmetric encryption via Fernet (AES-128 in CBC mode with HMAC). Let me know if you want me to adapt it to other languages or add features!