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// 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, dst, src []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] ^ te0[uint8(s0>>24)] ^ te1[uint8(s1>>16)] ^ te2[uint8(s2>>8)] ^ te3[uint8(s3)]
                t1 = xk[k+1] ^ te0[uint8(s1>>24)] ^ te1[uint8(s2>>16)] ^ te2[uint8(s3>>8)] ^ te3[uint8(s0)]
                t2 = xk[k+2] ^ te0[uint8(s2>>24)] ^ te1[uint8(s3>>16)] ^ te2[uint8(s0>>8)] ^ te3[uint8(s1)]
                t3 = xk[k+3] ^ te0[uint8(s3>>24)] ^ te1[uint8(s0>>16)] ^ te2[uint8(s1>>8)] ^ te3[uint8(s2)]
                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, dst, src []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] ^ td0[uint8(s0>>24)] ^ td1[uint8(s3>>16)] ^ td2[uint8(s2>>8)] ^ td3[uint8(s1)]
                t1 = xk[k+1] ^ td0[uint8(s1>>24)] ^ td1[uint8(s0>>16)] ^ td2[uint8(s3>>8)] ^ td3[uint8(s2)]
                t2 = xk[k+2] ^ td0[uint8(s2>>24)] ^ td1[uint8(s1>>16)] ^ td2[uint8(s0>>8)] ^ td3[uint8(s3)]
                t3 = xk[k+3] ^ td0[uint8(s3>>24)] ^ td1[uint8(s2>>16)] ^ td2[uint8(s1>>8)] ^ td3[uint8(s0)]
                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 = td0[sbox0[x>>24]] ^ td1[sbox0[x>>16&0xff]] ^ td2[sbox0[x>>8&0xff]] ^ td3[sbox0[x&0xff]]
                        }
                        dec[i+j] = x
                }
        }
}