AES - The Wide Trail Wonder

The Advanced Encryption Standard, also known as Rijndael, was developed by two Belgian cryptographers and succeeds DES. The code for encrypting using AES in Python is almost identical as for DES, except that instead of a 64 bit key (8 bytes) the key size must be 16, 24 or 32 bytes long.

The creators of Rijndael published a book in 2002 explaining the mathematical arguments underlying its construction (Design of Rijndael, Joan Daemen and Vincent Rijmen, Springer). In it they describe the "wide trail strategy" used in the algorithm's design.

Here is a paper explaining wide trail written by the creators of Rijndael. Read it.