How to encrypt and decrypt files in Python
Fernet using the cryptography library can safely implement Python file encryption and decryption. 2. Generate and securely store keys for use in encryption and decryption processes. 3. When encrypting, read the file content and write it into the .enc file, and when decrypting, restore the original file. 4. Pay attention to key security management and avoid hard coding or submitting to version control. 5. Fernet is based on AES and HMAC and is suitable for most scenarios, but streaming processing of large files needs to be considered.
Encrypting and decrypting files in Python can be done securely using the cryptography library, which provides modern encryption methods like Fernet. Fernet guarantees that data encrypted cannot be manipulated or read without the key. Here's how to implement file encryption and decryption step by step.
Install the cryptography library
If you haven't installed the cryptography package yet, use pip to install it:
pip install cryptographyThis library includes Fernet, a symmetric encryption method that's safe and easy to use.
Generate an encryption key
A Fernet key is required to encrypt and decrypt files. Generate and save it securely—never hardcode it in your script for production use.
from cryptography.fernet import Fernet#Generate a key
key = Fernet.generate_key()
# Save the key to a file (keep this safe)
with open("secret.key", "wb") as key_file:
key_file.write(key)
You only need to generate the key once. Reuse it for both encryption and decryption.
Load the key from file
Before encrypting or decrypting, load the saved key:
def load_key():return open("secret.key", "rb").read()
Make sure the key file exists and is accessible when running your script.
Encrypt a file
To encrypt a file, read its contents, encrypt them with Fernet, and write the output to a new file.
def encrypt_file(filename, key):f = Fernet(key)
# Read the original file
with open(filename, "rb") as file:
file_data = file.read()
# Encrypt data
encrypted_data = f.encrypt(file_data)
# Write encrypted data to a new file
with open(filename ".enc", "wb") as file:
file.write(encrypted_data)
Example usage:
key = load_key()encrypt_file("my_secret_document.txt", key)
This creates an encrypted version of the file with a .enc extension.
Decrypt a file
Decryption reverses the process. It requires the same key used for encryption.
def decrypt_file(filename, key):f = Fernet(key)
# Read the encrypted file
with open(filename, "rb") as file:
encrypted_data = file.read()
# Decrypt data
decrypted_data = f.decrypt(encrypted_data)
# Write back the original data
with open(filename.replace(".enc", ""), "wb") as file:
file.write(decrypted_data)
Example usage:
key = load_key()decrypt_file("my_secret_document.txt.enc", key)
The decrypted file will be saved without the .enc extension.
Security considerations
Keep these points in mind:
- Store the encryption key securely—preferably in an environment variable or secure key manager.
- Never commit the key to version control.
- Fernet uses AES in CBC mode with PKCS7 padding and HMAC authentication, making it safe for most use cases.
- Large files are loaded into memory entirely, so consider streaming for very large files.
Basically, with the cryptography library and Fernet, file encryption in Python is straightforward and secure. Just handle the key responsibly.
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