Master Python Cryptography: Hashing, DES, RSA & Secure Coding with PyCryptodome

Introduction

Python's standard library provides limited cryptographic functions, but it includes hashlib for hashing. This article gives a brief overview and focuses on two third‑party packages: PyCryptodome and cryptography , showing how to encrypt and decrypt strings.

Hashing

1. Hashing Overview The hashlib module supports FIPS‑approved hash algorithms such as SHA‑1, SHA‑224, SHA‑256, SHA‑384, SHA‑512, and MD5, as well as adler32 and crc32 from zlib. Hashes are commonly used to store password digests or verify file integrity.

2. Practical Example

Create an MD5 hash object, add a byte string, and call digest() to obtain the hash value.

Obtain the hexadecimal representation of the hash.

Create a SHA‑1 hash in a similar way.

Key Derivation

Python's standard library offers pbkdf2_hmac for password‑based key derivation (PKCS#5). It supports salting and iteration (e.g., 100 000 iterations with a 16‑byte salt) to resist dictionary and rainbow‑table attacks.

PyCryptodome

PyCryptodome replaces the older PyCrypto library. Install it via pip install pycryptodome (Linux) or the appropriate Windows installer. It provides implementations for DES, RSA, and other algorithms.

DES Algorithm

1. DES Encryption Example

Set an 8‑character key (DES uses an 8‑byte key).

Define a padding function to make the plaintext length a multiple of 8.

Create a DES instance, encrypt padded plaintext, and obtain the ciphertext.

2. DES Decryption Example Decrypt the ciphertext with DES.decrypt() to retrieve the original byte string.

RSA Algorithm

Generate a 2048‑bit RSA key pair using Crypto.PublicKey.RSA, export the private key with a password, and write both private and public keys to disk.

File Encryption Use the public key to encrypt a randomly generated session key (AES‑256) with PKCS#1 OAEP, then encrypt the file data with AES, and store the ciphertext, session key, IV, and MAC.

Decryption Read the encrypted file, load the private key (providing the password), recover the session key, recreate the AES cipher, and decrypt the data.

cryptography Package

Install via pip install cryptography. The package offers high‑level primitives such as Fernet for symmetric encryption, which handles key generation, encryption, decryption, and automatic authentication.

Example Generate a Fernet key, encrypt a message, and then decrypt it back to plaintext.

Conclusion

This guide provides a concise introduction to using PyCryptodome and cryptography for hashing, symmetric and asymmetric encryption, and secure file handling in Python. For deeper exploration, consult the official documentation and practice with real‑world scenarios.