Class CTR

The algorithm steps are formally described as follows:

    CTR Encryption: O[j] = E(K)(T[j]); for j = 1, 2...n;
                    C[j] = P[j] ^ O[j]; for j = 1, 2...n.
    CTR Decryption: O[j] = E(K)(T[j]); for j = 1, 2...n;
                    P[j] = C[j] ^ O[j]; for j = 1, 2...n.
 

where P is the plaintext, C is the ciphertext, E(K) is the underlying block cipher encryption function parametrised with the session key K, and T is the Counter.

This implementation, uses a standard incrementing function with a step of 1, and an initial value similar to that described in the NIST document.

References:

1. Recommendation for Block Cipher Modes of Operation Methods and Techniques, Morris Dworkin.