How to decrypt a file that was encrypted before?

December 26, 2023

from cryptography.fernet import Fernet

key = Fernet.generate_key()
cipher = Fernet(key)


def encrypt_file(file_path):
    with open(file_path, "rb") as f:
        content = f.read()
    encrypted_content = cipher.encrypt(content)
    with open(file_path, "wb") as f:
        f.write(encrypted_content)


encrypt_file(file_path)


def decrypt_file(file_path):
    with open(file_path, "rb") as f:
        encrypted_content = f.read()
    with open(file_path, "wb") as f:
        decrypted_content = cipher.decrypt(encrypted_content)
        f.write(decrypted_content)


decrypt_file(file_path)

I’m new on cryptography so I wonder how can I decrypt a file that was encrypted before? Do I need to use my key to encrypt content of a file?

>Solution :

You need to save the decrypted content to a new file instead of overwriting the original one. Try like this

from cryptography.fernet import Fernet

key = Fernet.generate_key()
cipher = Fernet(key)

def encrypt_file(file_path):
    with open(file_path, "rb") as f:
        content = f.read()
    encrypted_content = cipher.encrypt(content)
    with open(file_path + ".encrypted", "wb") as f:  # Save encrypted content to a new file
        f.write(encrypted_content)

def decrypt_file(encrypted_file_path, output_file_path):
    with open(encrypted_file_path, "rb") as f:
        encrypted_content = f.read()
    decrypted_content = cipher.decrypt(encrypted_content)
    with open(output_file_path, "wb") as f: 
        f.write(decrypted_content)

# Encrypt file
file_path = "path/to/your/file.txt"
encrypt_file(file_path)

# Decrypt file
encrypted_file_path = "path/to/your/file.txt.encrypted"  
output_file_path = "path/to/your/decrypted_file.txt"  
decrypt_file(encrypted_file_path, output_file_path)