// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This Go implementation is derived in part from the reference
// ANSI C implementation, which carries the following notice:
//
//	rijndael-alg-fst.c
//
//	@version 3.0 (December 2000)
//
//	Optimised ANSI C code for the Rijndael cipher (now AES)
//
//	@author Vincent Rijmen <vincent.rijmen@esat.kuleuven.ac.be>
//	@author Antoon Bosselaers <antoon.bosselaers@esat.kuleuven.ac.be>
//	@author Paulo Barreto <paulo.barreto@terra.com.br>
//
//	This code is hereby placed in the public domain.
//
//	THIS SOFTWARE IS PROVIDED BY THE AUTHORS ''AS IS'' AND ANY EXPRESS
//	OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
//	WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
//	ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE
//	LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
//	CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
//	SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
//	BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
//	WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
//	OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
//	EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// See FIPS 197 for specification, and see Daemen and Rijmen's Rijndael submission
// for implementation details.
//	http://www.csrc.nist.gov/publications/fips/fips197/fips-197.pdf
//	http://csrc.nist.gov/archive/aes/rijndael/Rijndael-ammended.pdf

package aes

// Encrypt one block from src into dst, using the expanded key xk.
func encryptBlock(xk []uint32, src, dst []byte) {
	var s0, s1, s2, s3, t0, t1, t2, t3 uint32;

	s0 = uint32(src[0])<<24 | uint32(src[1])<<16 | uint32(src[2])<<8 | uint32(src[3]);
	s1 = uint32(src[4])<<24 | uint32(src[5])<<16 | uint32(src[6])<<8 | uint32(src[7]);
	s2 = uint32(src[8])<<24 | uint32(src[9])<<16 | uint32(src[10])<<8 | uint32(src[11]);
	s3 = uint32(src[12])<<24 | uint32(src[13])<<16 | uint32(src[14])<<8 | uint32(src[15]);

	// First round just XORs input with key.
	s0 ^= xk[0];
	s1 ^= xk[1];
	s2 ^= xk[2];
	s3 ^= xk[3];

	// Middle rounds shuffle using tables.
	// Number of rounds is set by length of expanded key.
	nr := len(xk)/4 - 2;	// - 2: one above, one more below
	k := 4;
	for r := 0; r < nr; r++ {
		t0 = xk[k+0] ^ te[0][s0>>24] ^ te[1][s1>>16&0xff] ^ te[2][s2>>8&0xff] ^ te[3][s3&0xff];
		t1 = xk[k+1] ^ te[0][s1>>24] ^ te[1][s2>>16&0xff] ^ te[2][s3>>8&0xff] ^ te[3][s0&0xff];
		t2 = xk[k+2] ^ te[0][s2>>24] ^ te[1][s3>>16&0xff] ^ te[2][s0>>8&0xff] ^ te[3][s1&0xff];
		t3 = xk[k+3] ^ te[0][s3>>24] ^ te[1][s0>>16&0xff] ^ te[2][s1>>8&0xff] ^ te[3][s2&0xff];
		k += 4;
		s0, s1, s2, s3 = t0, t1, t2, t3;
	}

	// Last round uses s-box directly and XORs to produce output.
	s0 = uint32(sbox0[t0>>24])<<24 | uint32(sbox0[t1>>16&0xff])<<16 | uint32(sbox0[t2>>8&0xff])<<8 | uint32(sbox0[t3&0xff]);
	s1 = uint32(sbox0[t1>>24])<<24 | uint32(sbox0[t2>>16&0xff])<<16 | uint32(sbox0[t3>>8&0xff])<<8 | uint32(sbox0[t0&0xff]);
	s2 = uint32(sbox0[t2>>24])<<24 | uint32(sbox0[t3>>16&0xff])<<16 | uint32(sbox0[t0>>8&0xff])<<8 | uint32(sbox0[t1&0xff]);
	s3 = uint32(sbox0[t3>>24])<<24 | uint32(sbox0[t0>>16&0xff])<<16 | uint32(sbox0[t1>>8&0xff])<<8 | uint32(sbox0[t2&0xff]);

	s0 ^= xk[k+0];
	s1 ^= xk[k+1];
	s2 ^= xk[k+2];
	s3 ^= xk[k+3];

	dst[0], dst[1], dst[2], dst[3] = byte(s0>>24), byte(s0>>16), byte(s0>>8), byte(s0);
	dst[4], dst[5], dst[6], dst[7] = byte(s1>>24), byte(s1>>16), byte(s1>>8), byte(s1);
	dst[8], dst[9], dst[10], dst[11] = byte(s2>>24), byte(s2>>16), byte(s2>>8), byte(s2);
	dst[12], dst[13], dst[14], dst[15] = byte(s3>>24), byte(s3>>16), byte(s3>>8), byte(s3);
}

// Decrypt one block from src into dst, using the expanded key xk.
func decryptBlock(xk []uint32, src, dst []byte) {
	var s0, s1, s2, s3, t0, t1, t2, t3 uint32;

	s0 = uint32(src[0])<<24 | uint32(src[1])<<16 | uint32(src[2])<<8 | uint32(src[3]);
	s1 = uint32(src[4])<<24 | uint32(src[5])<<16 | uint32(src[6])<<8 | uint32(src[7]);
	s2 = uint32(src[8])<<24 | uint32(src[9])<<16 | uint32(src[10])<<8 | uint32(src[11]);
	s3 = uint32(src[12])<<24 | uint32(src[13])<<16 | uint32(src[14])<<8 | uint32(src[15]);

	// First round just XORs input with key.
	s0 ^= xk[0];
	s1 ^= xk[1];
	s2 ^= xk[2];
	s3 ^= xk[3];

	// Middle rounds shuffle using tables.
	// Number of rounds is set by length of expanded key.
	nr := len(xk)/4 - 2;	// - 2: one above, one more below
	k := 4;
	for r := 0; r < nr; r++ {
		t0 = xk[k+0] ^ td[0][s0>>24] ^ td[1][s3>>16&0xff] ^ td[2][s2>>8&0xff] ^ td[3][s1&0xff];
		t1 = xk[k+1] ^ td[0][s1>>24] ^ td[1][s0>>16&0xff] ^ td[2][s3>>8&0xff] ^ td[3][s2&0xff];
		t2 = xk[k+2] ^ td[0][s2>>24] ^ td[1][s1>>16&0xff] ^ td[2][s0>>8&0xff] ^ td[3][s3&0xff];
		t3 = xk[k+3] ^ td[0][s3>>24] ^ td[1][s2>>16&0xff] ^ td[2][s1>>8&0xff] ^ td[3][s0&0xff];
		k += 4;
		s0, s1, s2, s3 = t0, t1, t2, t3;
	}

	// Last round uses s-box directly and XORs to produce output.
	s0 = uint32(sbox1[t0>>24])<<24 | uint32(sbox1[t3>>16&0xff])<<16 | uint32(sbox1[t2>>8&0xff])<<8 | uint32(sbox1[t1&0xff]);
	s1 = uint32(sbox1[t1>>24])<<24 | uint32(sbox1[t0>>16&0xff])<<16 | uint32(sbox1[t3>>8&0xff])<<8 | uint32(sbox1[t2&0xff]);
	s2 = uint32(sbox1[t2>>24])<<24 | uint32(sbox1[t1>>16&0xff])<<16 | uint32(sbox1[t0>>8&0xff])<<8 | uint32(sbox1[t3&0xff]);
	s3 = uint32(sbox1[t3>>24])<<24 | uint32(sbox1[t2>>16&0xff])<<16 | uint32(sbox1[t1>>8&0xff])<<8 | uint32(sbox1[t0&0xff]);

	s0 ^= xk[k+0];
	s1 ^= xk[k+1];
	s2 ^= xk[k+2];
	s3 ^= xk[k+3];

	dst[0], dst[1], dst[2], dst[3] = byte(s0>>24), byte(s0>>16), byte(s0>>8), byte(s0);
	dst[4], dst[5], dst[6], dst[7] = byte(s1>>24), byte(s1>>16), byte(s1>>8), byte(s1);
	dst[8], dst[9], dst[10], dst[11] = byte(s2>>24), byte(s2>>16), byte(s2>>8), byte(s2);
	dst[12], dst[13], dst[14], dst[15] = byte(s3>>24), byte(s3>>16), byte(s3>>8), byte(s3);
}

// Apply sbox0 to each byte in w.
func subw(w uint32) uint32 {
	return uint32(sbox0[w>>24])<<24 |
		uint32(sbox0[w>>16&0xff])<<16 |
		uint32(sbox0[w>>8&0xff])<<8 |
		uint32(sbox0[w&0xff])
}

// Rotate
func rotw(w uint32) uint32	{ return w<<8 | w>>24 }

// Key expansion algorithm.  See FIPS-197, Figure 11.
// Their rcon[i] is our powx[i-1] << 24.
func expandKey(key []byte, enc, dec []uint32) {
	// Encryption key setup.
	var i int;
	nk := len(key) / 4;
	for i = 0; i < nk; i++ {
		enc[i] = uint32(key[4*i])<<24 | uint32(key[4*i+1])<<16 | uint32(key[4*i+2])<<8 | uint32(key[4*i+3])
	}
	for ; i < len(enc); i++ {
		t := enc[i-1];
		if i%nk == 0 {
			t = subw(rotw(t)) ^ (uint32(powx[i/nk-1]) << 24)
		} else if nk > 6 && i%nk == 4 {
			t = subw(t)
		}
		enc[i] = enc[i-nk] ^ t;
	}

	// Derive decryption key from encryption key.
	// Reverse the 4-word round key sets from enc to produce dec.
	// All sets but the first and last get the MixColumn transform applied.
	if dec == nil {
		return
	}
	n := len(enc);
	for i := 0; i < n; i += 4 {
		ei := n - i - 4;
		for j := 0; j < 4; j++ {
			x := enc[ei+j];
			if i > 0 && i+4 < n {
				x = td[0][sbox0[x>>24]] ^ td[1][sbox0[x>>16&0xff]] ^ td[2][sbox0[x>>8&0xff]] ^ td[3][sbox0[x&0xff]]
			}
			dec[i+j] = x;
		}
	}
}