package romulus_go

// Converted to go with C2GO, tweaks by 51m0n - 2022.

/*
 * Date: 11 December 2015
 * Contact: Thomas Peyrin - thomas.peyrin@gmail.com
 * Modified on 04 May 2021 by Mustafa Khairallah - Modified the code
 * to implement only the SKINNY-128-384+ encryption version of Skinny for
 * Romulus v1.3, the NIST LwC finalist.
 * mustafa.khairallah@ntu.edu.sg
 */

/*
 * This file includes only the encryption function of SKINNY-128-384+ as required by Romulus-v1.3
 */

// Skinny-128-384+ parameters: 128-bit block, 384-bit tweakey and 40 rounds
var BLOCK_SIZE int = 128

var TWEAKEY_SIZE int = 384

var N_RNDS int = 40

// Packing of data is done as follows (state[i][j] stands for row i and column j):
// 0  1  2  3
// 4  5  6  7
// 8  9 10 11
//12 13 14 15

// 8-bit Sbox
var sbox_8 = [256]byte{0x65, 0x4c, 0x6a, 0x42, 0x4b, 0x63, 0x43, 0x6b, 0x55, 0x75, 0x5a, 0x7a, 0x53, 0x73, 0x5b, 0x7b, 0x35, 0x8c, 0x3a, 0x81, 0x89, 0x33, 0x80, 0x3b, 0x95, 0x25, 0x98, 0x2a, 0x90, 0x23, 0x99, 0x2b, 0xe5, 0xcc, 0xe8, 0xc1, 0xc9, 0xe0, 0xc0, 0xe9, 0xd5, 0xf5, 0xd8, 0xf8, 0xd0, 0xf0, 0xd9, 0xf9, 0xa5, 0x1c, 0xa8, 0x12, 0x1b, 0xa0, 0x13, 0xa9, 0x05, 0xb5, 0x0a, 0xb8, 0x03, 0xb0, 0x0b, 0xb9, 0x32, 0x88, 0x3c, 0x85, 0x8d, 0x34, 0x84, 0x3d, 0x91, 0x22, 0x9c, 0x2c, 0x94, 0x24, 0x9d, 0x2d, 0x62, 0x4a, 0x6c, 0x45, 0x4d, 0x64, 0x44, 0x6d, 0x52, 0x72, 0x5c, 0x7c, 0x54, 0x74, 0x5d, 0x7d, 0xa1, 0x1a, 0xac, 0x15, 0x1d, 0xa4, 0x14, 0xad, 0x02, 0xb1, 0x0c, 0xbc, 0x04, 0xb4, 0x0d, 0xbd, 0xe1, 0xc8, 0xec, 0xc5, 0xcd, 0xe4, 0xc4, 0xed, 0xd1, 0xf1, 0xdc, 0xfc, 0xd4, 0xf4, 0xdd, 0xfd, 0x36, 0x8e, 0x38, 0x82, 0x8b, 0x30, 0x83, 0x39, 0x96, 0x26, 0x9a, 0x28, 0x93, 0x20, 0x9b, 0x29, 0x66, 0x4e, 0x68, 0x41, 0x49, 0x60, 0x40, 0x69, 0x56, 0x76, 0x58, 0x78, 0x50, 0x70, 0x59, 0x79, 0xa6, 0x1e, 0xaa, 0x11, 0x19, 0xa3, 0x10, 0xab, 0x06, 0xb6, 0x08, 0xba, 0x00, 0xb3, 0x09, 0xbb, 0xe6, 0xce, 0xea, 0xc2, 0xcb, 0xe3, 0xc3, 0xeb, 0xd6, 0xf6, 0xda, 0xfa, 0xd3, 0xf3, 0xdb, 0xfb, 0x31, 0x8a, 0x3e, 0x86, 0x8f, 0x37, 0x87, 0x3f, 0x92, 0x21, 0x9e, 0x2e, 0x97, 0x27, 0x9f, 0x2f, 0x61, 0x48, 0x6e, 0x46, 0x4f, 0x67, 0x47, 0x6f, 0x51, 0x71, 0x5e, 0x7e, 0x57, 0x77, 0x5f, 0x7f, 0xa2, 0x18, 0xae, 0x16, 0x1f, 0xa7, 0x17, 0xaf, 0x01, 0xb2, 0x0e, 0xbe, 0x07, 0xb7, 0x0f, 0xbf, 0xe2, 0xca, 0xee, 0xc6, 0xcf, 0xe7, 0xc7, 0xef, 0xd2, 0xf2, 0xde, 0xfe, 0xd7, 0xf7, 0xdf, 0xff}

// ShiftAndSwitchRows permutation
var P = [16]byte{0, 1, 2, 3, 7, 4, 5, 6, 10, 11, 8, 9, 13, 14, 15, 12}

// Tweakey permutation
var TWEAKEY_P = [16]byte{9, 15, 8, 13, 10, 14, 12, 11, 0, 1, 2, 3, 4, 5, 6, 7}

// round constants
var RC = [40]byte{
	0x01,
	0x03,
	0x07,
	0x0F,
	0x1F,
	0x3E,
	0x3D,
	0x3B,
	0x37,
	0x2F,
	0x1E,
	0x3C,
	0x39,
	0x33,
	0x27,
	0x0E,
	0x1D,
	0x3A,
	0x35,
	0x2B,
	0x16,
	0x2C,
	0x18,
	0x30,
	0x21,
	0x02,
	0x05,
	0x0B,
	0x17,
	0x2E,
	0x1C,
	0x38,
	0x31,
	0x23,
	0x06,
	0x0D,
	0x1B,
	0x36,
	0x2D,
	0x1A,
}

// Extract and apply the subtweakey to the internal state (must be the two top rows XORed together), then update the tweakey state
func AddKey(state [][4]byte, keyCells [][4][4]byte) {
	var i int
	var j int
	var k int
	var pos byte
	var keyCells_tmp [3][4][4]byte

	// apply the subtweakey to the internal state
	for i = 0; i <= 1; i++ {
		for j = 0; j < 4; j++ {
			state[i][j] ^= keyCells[0][i][j] ^ keyCells[1][i][j] ^ keyCells[2][i][j]
		}
	}

	// update the subtweakey states with the permutation
	for k = 0; k < int(TWEAKEY_SIZE/BLOCK_SIZE); k++ {
		for i = 0; i < 4; i++ {
			for j = 0; j < 4; j++ {
				//application of the TWEAKEY permutation
				pos = TWEAKEY_P[j+4*i]

				keyCells_tmp[k][i][j] = keyCells[k][pos>>2][pos&0x3]
			}
		}
	}

	// update the subtweakey states with the LFSRs
	for k = 0; k < int(TWEAKEY_SIZE/BLOCK_SIZE); k++ {
		for i = 0; i <= 1; i++ {
			for j = 0; j < 4; j++ {
				//application of LFSRs for TK updates
				if k == 1 {
					keyCells_tmp[k][i][j] = ((keyCells_tmp[k][i][j] << 1) & 0xFE) ^ ((keyCells_tmp[k][i][j] >> 7) & 0x01) ^ ((keyCells_tmp[k][i][j] >> 5) & 0x01)
				} else if k == 2 {
					keyCells_tmp[k][i][j] = ((keyCells_tmp[k][i][j] >> 1) & 0x7F) ^ ((keyCells_tmp[k][i][j] << 7) & 0x80) ^ ((keyCells_tmp[k][i][j] << 1) & 0x80)
				}
			}
		}
	}

	for k = 0; k < int(TWEAKEY_SIZE/BLOCK_SIZE); k++ {
		for i = 0; i < 4; i++ {
			for j = 0; j < 4; j++ {
				keyCells[k][i][j] = keyCells_tmp[k][i][j]
			}
		}
	}
}

// Apply the constants: using a LFSR counter on 6 bits, we XOR the 6 bits to the first 6 bits of the internal state
func AddConstants(state [][4]byte, r int) {
	state[0][0] ^= (RC[r] & 0xf)
	state[1][0] ^= ((RC[r] >> 4) & 0x3)
	state[2][0] ^= 0x2
}

// apply the 8-bit Sbox
func SubCell8(state [][4]byte) {
	var i int
	var j int
	for i = 0; i < 4; i++ {
		for j = 0; j < 4; j++ {
			state[i][j] = sbox_8[state[i][j]]
		}
	}
}

// Apply the ShiftRows function
func ShiftRows(state [][4]byte) {
	var i int
	var j int
	var pos int
	var state_tmp [4][4]byte
	for i = 0; i < 4; i++ {
		for j = 0; j < 4; j++ {
			//application of the ShiftRows permutation
			pos = int(P[j+4*i])

			state_tmp[i][j] = state[pos>>2][pos&0x3]
		}
	}

	for i = 0; i < 4; i++ {
		for j = 0; j < 4; j++ {
			state[i][j] = state_tmp[i][j]
		}
	}
}

// Apply the linear diffusion matrix
//M =
//1 0 1 1
//1 0 0 0
//0 1 1 0
//1 0 1 0
func MixColumn(state [][4]byte) {
	var j int
	var temp byte

	for j = 0; j < 4; j++ {
		state[1][j] ^= state[2][j]
		state[2][j] ^= state[0][j]
		state[3][j] ^= state[2][j]

		temp = state[3][j]
		state[3][j] = state[2][j]
		state[2][j] = state[1][j]
		state[1][j] = state[0][j]
		state[0][j] = temp
	}
}

// encryption function of Skinny-128-384+
func enc(input []byte, userkey []byte) {
	var state [4][4]byte
	var keyCells [3][4][4]byte
	var i int

	//memset(keyCells, 0, 48);
	for i = 0; i < 16; i++ {
		state[i>>2][i&0x3] = input[i] & 0xFF
		keyCells[0][i>>2][i&0x3] = userkey[i] & 0xFF
		keyCells[1][i>>2][i&0x3] = userkey[i+16] & 0xFF
		keyCells[2][i>>2][i&0x3] = userkey[i+32] & 0xFF
	}

	for i = 0; i < N_RNDS; i++ {
		SubCell8(state[:])

		AddConstants(state[:], i)

		AddKey(state[:], keyCells[:])

		ShiftRows(state[:])

		MixColumn(state[:])
	}

	for i = 0; i < 16; i++ {
		input[i] = state[i>>2][i&0x3] & 0xFF
	}
}

func skinny_128_384_plus_enc(input []byte, userkey []byte) {
	enc(input, userkey)
}