//Decrypt a ciphertext using a key and the 4 round SPN
public static BitString16 Decrypt(BitString16 ciphertext, Key key)
{
SBox sbox = new SBox();
//Pre
BitString16 first_subkey = key.getDecryptionSubKey(1);
BitString16 plaintext = Util.xor(ciphertext, first_subkey);
//Round 1
BitString16 second_subkey = key.getDecryptionSubKey(2);
plaintext = sbox.backwardsTransform(plaintext);
plaintext = Util.xor(plaintext, second_subkey);
//Rounds 2-4
for (int round = 2; round < 5; ++round)
{
BitString16 subkey = key.getDecryptionSubKey(round + 1);
plaintext = Permutation.backwardsPermutation(plaintext);
plaintext = sbox.backwardsTransform(plaintext);
plaintext = Util.xor(plaintext, subkey);
}
return(plaintext);
}
static BitString16 partial_decrypt(BitString16 ciphertext, BitString16 key)
{
SBox sbox = new SBox();
//Pre
BitString16 plaintext = Util.xor(ciphertext, key);
//Round 1
plaintext = sbox.backwardsTransform(plaintext);
return(plaintext);
}
static BitString16 partial_decrypt(BitString16 ciphertext, BitString16 key)
{
SBox sbox = new SBox();
//Pre
BitString16 plaintext = Util.xor(ciphertext, key);
//Round 1
plaintext = sbox.backwardsTransform(plaintext);
return plaintext;
}
//Decrypt a ciphertext using a key and the 4 round SPN
public static BitString16 Decrypt(BitString16 ciphertext, Key key)
{
SBox sbox = new SBox();
//Pre
BitString16 first_subkey = key.getDecryptionSubKey(1);
BitString16 plaintext = Util.xor(ciphertext, first_subkey);
//Round 1
BitString16 second_subkey = key.getDecryptionSubKey(2);
plaintext = sbox.backwardsTransform(plaintext);
plaintext = Util.xor(plaintext, second_subkey);
//Rounds 2-4
for (int round = 2; round < 5; ++round)
{
BitString16 subkey = key.getDecryptionSubKey(round + 1);
plaintext = Permutation.backwardsPermutation(plaintext);
plaintext = sbox.backwardsTransform(plaintext);
plaintext = Util.xor(plaintext, subkey);
}
return plaintext;
}