IteratedBlockCryptosystem

It is an iterated block encryptor and decryptor.

Cryptosystem description.
It uses two Lai-Massey and two Feistel tacts. The round function is SP network.
Key schedule: θ = θ₁ || θ₂, KS(θ) = (θ₁, θ₂, θ₁, θ₂).
All S-blocks are the same:
Substitution: (3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5)
Permutation: (5 * i + 9) (mod 16)

Note: this cryptosystem has weak keys (any keys that have the same left and right part).

Encryptor input:

• binary file with an opened text to be encrypted;
• binary file with a key (4 bytes).

Encryptor output:

• binary file with an encrypted text.

Decryptor input:

• binary file with an encrypted text to be decrypted;
• binary file with a key (4 bytes).

Decryptor output:

• binary file with a decrypted text