private void InvShiftRows(ref State_t state)
{
uint temp;
// Rotate first row 1 columns to right
temp = state.state_t[3, 1];
state.state_t[3, 1] = state.state_t[2, 1];
state.state_t[2, 1] = state.state_t[1, 1];
state.state_t[1, 1] = state.state_t[0, 1];
state.state_t[0, 1] = temp;
// Rotate second row 2 columns to right
temp = state.state_t[0, 2];
state.state_t[0, 2] = state.state_t[2, 2];
state.state_t[2, 2] = temp;
temp = state.state_t[1, 2];
state.state_t[1, 2] = state.state_t[3, 2];
state.state_t[3, 2] = temp;
// Rotate third row 3 columns to right
temp = state.state_t[0, 3];
state.state_t[0, 3] = state.state_t[1, 3];
state.state_t[1, 3] = state.state_t[2, 3];
state.state_t[2, 3] = state.state_t[3, 3];
state.state_t[3, 3] = temp;
}
// The SubBytes Function Substitutes the values in the
// state matrix with values in an S-box.
private void InvSubBytes(ref State_t state)
{
uint i, j;
for (i = 0; i < 4; ++i)
{
for (j = 0; j < 4; ++j)
{
state.state_t[j, i] = getSBoxInvert(state.state_t[j, i] & 0xff);
}
}
}
// The SubBytes Function Substitutes the values in the
// state matrix with values in an S-box.
private void SubBytes(ref State_t state)
{
uint i, j;
for (i = 0; i < 4; ++i)
{
for (j = 0; j < 4; ++j)
{
state.state_t[j, i] = getSBoxValue(state.state_t[j, i] & 0xff); // added "& 0xff"
}
}
}
// This function adds the round key to state.
// The round key is added to the state by an XOR function.
private void AddRoundKey(uint round, ref State_t state, ref uint[] RoundKey)
{
uint i, j;
for (i = 0; i < 4; ++i)
{
for (j = 0; j < 4; ++j)
{
state.state_t[i, j] ^= RoundKey[(round * Nb * 4) + (i * Nb) + j];
}
}
}
// MixColumns function mixes the columns of the state matrix
private void MixColumns(ref State_t state)
{
uint i;
uint Tmp, Tm, t;
for (i = 0; i < 4; ++i)
{
t = state.state_t[i, 0];
Tmp = state.state_t[i, 0] ^ state.state_t[i, 1] ^ state.state_t[i, 2] ^ state.state_t[i, 3];
Tm = state.state_t[i, 0] ^ state.state_t[i, 1]; Tm = xtime(Tm); state.state_t[i, 0] ^= Tm ^ Tmp;
Tm = state.state_t[i, 1] ^ state.state_t[i, 2]; Tm = xtime(Tm); state.state_t[i, 1] ^= Tm ^ Tmp;
Tm = state.state_t[i, 2] ^ state.state_t[i, 3]; Tm = xtime(Tm); state.state_t[i, 2] ^= Tm ^ Tmp;
Tm = state.state_t[i, 3] ^ t; Tm = xtime(Tm); state.state_t[i, 3] ^= Tm ^ Tmp;
}
}
// MixColumns function mixes the columns of the state matrix.
// The method used to multiply may be difficult to understand for the inexperienced.
// Please use the references to gain more information.
private void InvMixColumns(ref State_t state)
{
int i;
uint a, b, c, d;
for (i = 0; i < 4; ++i)
{
a = state.state_t[i, 0];
b = state.state_t[i, 1];
c = state.state_t[i, 2];
d = state.state_t[i, 3];
state.state_t[i, 0] = Multiply(a, 0x0e) ^ Multiply(b, 0x0b) ^ Multiply(c, 0x0d) ^ Multiply(d, 0x09);
state.state_t[i, 1] = Multiply(a, 0x09) ^ Multiply(b, 0x0e) ^ Multiply(c, 0x0b) ^ Multiply(d, 0x0d);
state.state_t[i, 2] = Multiply(a, 0x0d) ^ Multiply(b, 0x09) ^ Multiply(c, 0x0e) ^ Multiply(d, 0x0b);
state.state_t[i, 3] = Multiply(a, 0x0b) ^ Multiply(b, 0x0d) ^ Multiply(c, 0x09) ^ Multiply(d, 0x0e);
}
}
public void InvCipher(ref State_t state, ref uint[] RoundKey)
{
uint round = 0;
// Add the First round key to the state before starting the rounds.
AddRoundKey(Nr, ref state, ref RoundKey);
// There will be Nr rounds.
// The first Nr-1 rounds are identical.
// These Nr-1 rounds are executed in the loop below.
for (round = (Nr - 1); round > 0; --round)
{
InvShiftRows(ref state);
InvSubBytes(ref state);
AddRoundKey(round, ref state, ref RoundKey);
InvMixColumns(ref state);
}
// The last round is given below.
// The MixColumns function is not here in the last round.
InvShiftRows(ref state);
InvSubBytes(ref state);
AddRoundKey(0, ref state, ref RoundKey);
}
// Cipher is the main function that encrypts the PlainText.
private void Cipher(ref State_t state, ref uint[] RoundKey)
{
uint round = 0;
// Add the First round key to the state before starting the rounds.
AddRoundKey(0, ref state, ref RoundKey);
// There will be Nr rounds.
// The first Nr-1 rounds are identical.
// These Nr-1 rounds are executed in the loop below.
for (round = 1; round < Nr; ++round)
{
SubBytes(ref state);
ShiftRows(ref state);
MixColumns(ref state);
AddRoundKey(round, ref state, ref RoundKey);
}
// The last round is given below.
// The MixColumns function is not here in the last round.
SubBytes(ref state);
ShiftRows(ref state);
AddRoundKey(Nr, ref state, ref RoundKey);
}