Introduction to Cryptography with Open-Source Software

Block ciphers and the data encryption st andard 207

sage: from Crypto.Cipher import DES

For ease of discussion, strings of 16 hexadecimal characters will be used

for plaintext, key and ciphertext. Suppose the plaintext is

0xAAAABBBBCCCCDDDD

and the key is

0x0123456789ABCDEF.

To perform an encryption, a new DES object must be instantiated with the

key, but first the key will need to be converted into bytes:

sage: k = ’0123456789ABCDEF’

sage: key = k.decode(’hex’)

To encrypt, the plaintext must also first be converted into bytes:

sage: plaintext = ’AAAABBBBCCCCDDDD’

sage: pl = plaintext.decode(’hex’)

Now create a new DES instance with the key, and use the encrypt ...