Usage¶

This guide demonstrates the basic usage of DES PurePy.

Installation¶

Install the package from PyPI.

pip install des_PurePy

Creating a DES Object¶

Create a DES object by supplying an 8-byte key. The key may be provided as either a hexadecimal string or a bytes object.

Using a hexadecimal string:

import des_PurePy

des = des_PurePy.DES("0x133457799bbcdff1")

Using a bytes object:

import des_PurePy

des = des_PurePy.DES(b"password")

Encrypting Data¶

Encrypt plaintext using the encrypt() method.

ciphertext = des.encrypt("0x0123456789abcdef")

The returned ciphertext is a hexadecimal string.

0x85e813540f0ab405fdf2e174492922f8

Decrypting Data¶

Decrypt ciphertext using the decrypt() method.

cleartext = des.decrypt(ciphertext)

The result is returned as a hexadecimal string.

0x0123456789abcdef

Working with Text¶

Since the library accepts bytes objects, encrypting text is straightforward.

import des_PurePy

key = b"password"
des = des_PurePy.DES(key)

ciphertext = des.encrypt(b"secret message")

cleartext = des.decrypt(ciphertext)

message = bytes.fromhex(cleartext[2:]).decode("utf-8")

print(message)

Output:

secret message

Padding¶

DES operates on 64-bit (8-byte) blocks.

Plaintext is automatically padded using PKCS#5 padding before encryption. After decryption, the padding is removed automatically.

Block Mode¶

Messages longer than one block are encrypted using Electronic Codebook (ECB) mode.

Input Validation¶

DES PurePy validates all user input before encryption or decryption.

Examples of validation include:

Keys must be exactly 8 bytes (64 bits).
Ciphertext must be a multiple of the DES block size.
Hexadecimal strings must contain only valid hexadecimal characters.
Inputs may be either hexadecimal strings or bytes objects.

Invalid input raises an appropriate Python exception describing the error.