package rijndael

import (
	"encoding/binary"
)

const rounds = 14
const keyWords = 8
const BlockSize = 32
const blockWords = BlockSize/4

type Cipher struct {
	key [blockWords * (rounds + 1)]uint32
}

func NewCipher(key *[32]byte) *Cipher {
	c := new(Cipher)

	for i := 0; i < keyWords; i++ {
		c.key[i] = binary.BigEndian.Uint32(key[4*i:])
	}

	roundConstant := byte(1)
	for i := keyWords; i < blockWords * (rounds + 1); i++ {
		temp := c.key[i-1]
		if (i % keyWords == 0) {
			temp = subByte(rotByte(temp)) ^ (uint32(roundConstant) << 24)
			roundConstant = xtime(roundConstant)
		} else if (i % keyWords == 4) {
			temp = subByte(temp)
		}
		c.key[i] = c.key[i - keyWords] ^ temp
	}

	return c
}

func (c *Cipher) Encrypt(dst, src *[32]byte) {
	var state [4*blockWords]byte
	copy(state[:], src[:])

	addKey(&state, c.key[:])

	for round := 1; round < rounds; round++ {
		// ByteSub
		for i := range state {
			state[i] = sbox[state[i]]
		}

		// ShiftRow
		if blockWords == 32/4 {
			shiftRow(&state, 1, 1)
			shiftRow(&state, 2, 3)
			shiftRow(&state, 3, 4)
		} else {
			shiftRow(&state, 1, 1)
			shiftRow(&state, 2, 2)
			shiftRow(&state, 3, 3)
		}

		// MixColumns
		for i := 0; i < blockWords; i++ {
			mixColumn(state[4*i:])
		}

		addKey(&state, c.key[blockWords*round:])
	}

	// ByteSub
	for i := range state {
		state[i] = sbox[state[i]]
	}

	// ShiftRow
	if blockWords == 32/4 {
		shiftRow(&state, 1, 1)
		shiftRow(&state, 2, 3)
		shiftRow(&state, 3, 4)
	} else {
		shiftRow(&state, 1, 1)
		shiftRow(&state, 2, 2)
		shiftRow(&state, 3, 3)
	}

	addKey(&state, c.key[blockWords*rounds:])

	copy(dst[:], state[:])
}

func (c *Cipher) Decrypt(dst, src *[32]byte) {
	var state [4*blockWords]byte
	copy(state[:], src[:])

	addKey(&state, c.key[blockWords*rounds:])

	// ShiftRow
	if blockWords == 32/4 {
		shiftRow(&state, 1, -1)
		shiftRow(&state, 2, -3)
		shiftRow(&state, 3, -4)
	} else {
		shiftRow(&state, 1, -1)
		shiftRow(&state, 2, -2)
		shiftRow(&state, 3, -3)
	}

	// ByteSub
	for i := range state {
		state[i] = sboxInv[state[i]]
	}

	for round := rounds - 1; round >= 1; round-- {
		addKey(&state, c.key[blockWords*round:])

		// MixColumns
		for i := 0; i < blockWords; i++ {
			mixColumnInv(state[4*i:])
		}

		// ShiftRow
		if blockWords == 32/4 {
			shiftRow(&state, 1, -1)
			shiftRow(&state, 2, -3)
			shiftRow(&state, 3, -4)
		} else {
			shiftRow(&state, 1, -1)
			shiftRow(&state, 2, -2)
			shiftRow(&state, 3, -3)
		}

		// ByteSub
		for i := range state {
			state[i] = sboxInv[state[i]]
		}
	}

	addKey(&state, c.key[:])

	copy(dst[:], state[:])
}

func subByte(a uint32) uint32 {
	ret := uint32(0)
	for i := 0; i < 4; i++ {
		b := byte(a)
		ret >>= 8
		ret |= uint32(sbox[b]) << 24
		a >>= 8
	}
	return ret
}

func rotByte(a uint32) uint32 {
	return (a >> 24) | (a << 8)
}

func addKey(state *[4*blockWords]byte, key []uint32) {
	for i := 0; i < blockWords; i++ {
		t := binary.BigEndian.Uint32(state[4*i:])
		t ^= key[i]
		binary.BigEndian.PutUint32(state[4*i:], t)
	}
}

func shiftRow(state *[4*blockWords]byte, row, shift int) {
	var input [blockWords]byte
	for i := range input {
		input[i] = state[row + 4*i]
	}

	src := shift
	if src < 0 {
		src += blockWords
	}
	dst := row
	for i := 0; i < blockWords; i++ {
		state[dst] = input[src]
		dst += 4
		dst %= blockWords*4
		src++
		src %= blockWords
	}
}

func mixColumn(col []byte) {
	a := col[0]
	b := col[1]
	c := col[2]
	d := col[3]
	e := a ^ b ^ c ^ d

	col[0] ^= e ^ xtime(a^b)
	col[1] ^= e ^ xtime(b^c)
	col[2] ^= e ^ xtime(c^d)
	col[3] ^= e ^ xtime(d^a)
}

func mixColumnInv(col []byte) {
	a := col[0]
	b := col[1]
	c := col[2]
	d := col[3]
	e := a ^ b ^ c ^ d
	z := xtime(e)
	x := e ^ xtime(xtime(z^a^c))
	y := e ^ xtime(xtime(z^b^d))

	col[0] ^= x ^ xtime(a^b)
	col[1] ^= y ^ xtime(b^c)
	col[2] ^= x ^ xtime(c^d)
	col[3] ^= y ^ xtime(d^a)
}

func xtime(b byte) byte {
	c := uint32(b)
	c <<= 1
	c ^= ((c >> 8) & 1) * 0x1b
	return byte(c)
}

// FIPS-197 Figure 7. S-box substitution values in hexadecimal format.
var sbox = [256]byte{
	0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76,
	0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0,
	0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15,
	0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75,
	0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84,
	0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf,
	0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8,
	0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2,
	0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73,
	0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb,
	0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79,
	0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08,
	0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a,
	0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e,
	0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf,
	0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16,
}

// FIPS-197 Figure 14.  Inverse S-box substitution values in hexadecimal format.
var sboxInv = [256]byte{
	0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb,
	0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb,
	0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e,
	0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25,
	0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92,
	0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84,
	0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06,
	0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b,
	0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73,
	0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e,
	0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b,
	0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4,
	0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f,
	0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef,
	0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61,
	0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d,
}
