/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
/* AES implementation in JavaScript                                   (c) Chris Veness 2005-2016  */
/*                                                                                   MIT Licence  */
/* www.movable-type.co.uk/scripts/aes.html                                                        */
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */

'use strict';


/**
 * AES (Rijndael cipher) encryption routines,
 *
 * Reference implementation of FIPS-197 http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf.
 *
 * @namespace
 */
var Aes = {};


/**
 * AES Cipher function: encrypt 'input' state with Rijndael algorithm [§5.1];
 *   applies Nr rounds (10/12/14) using key schedule w for 'add round key' stage.
 *
 * @param   {number[]}   input - 16-byte (128-bit) input state array.
 * @param   {number[][]} w - Key schedule as 2D byte-array (Nr+1 x Nb bytes).
 * @returns {number[]}   Encrypted output state array.
 */
Aes.cipher = function(input, w) {
    var Nb = 4;               // block size (in words): no of columns in state (fixed at 4 for AES)
    var Nr = w.length/Nb - 1; // no of rounds: 10/12/14 for 128/192/256-bit keys

    var state = [ [], [], [], [] ];  // initialise 4xNb byte-array 'state' with input [§3.4]
    for (var i=0; i<4*Nb; i++) state[i%4][Math.floor(i/4)] = input[i];

    state = Aes.addRoundKey(state, w, 0, Nb);

    for (var round=1; round<Nr; round++) {
        state = Aes.subBytes(state, Nb);
        state = Aes.shiftRows(state, Nb);
        state = Aes.mixColumns(state, Nb);
        state = Aes.addRoundKey(state, w, round, Nb);
    }

    state = Aes.subBytes(state, Nb);
    state = Aes.shiftRows(state, Nb);
    state = Aes.addRoundKey(state, w, Nr, Nb);

    var output = new Array(4*Nb);  // convert state to 1-d array before returning [§3.4]
    for (var i=0; i<4*Nb; i++) output[i] = state[i%4][Math.floor(i/4)];

    return output;
};


/**
 * Perform key expansion to generate a key schedule from a cipher key [§5.2].
 *
 * @param   {number[]}   key - Cipher key as 16/24/32-byte array.
 * @returns {number[][]} Expanded key schedule as 2D byte-array (Nr+1 x Nb bytes).
 */
Aes.keyExpansion = function(key) {
    var Nb = 4;            // block size (in words): no of columns in state (fixed at 4 for AES)
    var Nk = key.length/4; // key length (in words): 4/6/8 for 128/192/256-bit keys
    var Nr = Nk + 6;       // no of rounds: 10/12/14 for 128/192/256-bit keys

    var w = new Array(Nb*(Nr+1));
    var temp = new Array(4);

    // initialise first Nk words of expanded key with cipher key
    for (var i=0; i<Nk; i++) {
        var r = [ key[4*i], key[4*i+1], key[4*i+2], key[4*i+3] ];
        w[i] = r;
    }

    // expand the key into the remainder of the schedule
    for (var i=Nk; i<(Nb*(Nr+1)); i++) {
        w[i] = new Array(4);
        for (var t=0; t<4; t++) temp[t] = w[i-1][t];
        // each Nk'th word has extra transformation
        if (i % Nk == 0) {
            temp = Aes.subWord(Aes.rotWord(temp));
            for (var t=0; t<4; t++) temp[t] ^= Aes.rCon[i/Nk][t];
        }
        // 256-bit key has subWord applied every 4th word
        else if (Nk > 6 && i%Nk == 4) {
            temp = Aes.subWord(temp);
        }
        // xor w[i] with w[i-1] and w[i-Nk]
        for (var t=0; t<4; t++) w[i][t] = w[i-Nk][t] ^ temp[t];
    }

    return w;
};


/**
 * Apply SBox to state S [§5.1.1]
 * @private
 */
Aes.subBytes = function(s, Nb) {
    for (var r=0; r<4; r++) {
        for (var c=0; c<Nb; c++) s[r][c] = Aes.sBox[s[r][c]];
    }
    return s;
};


/**
 * Shift row r of state S left by r bytes [§5.1.2]
 * @private
 */
Aes.shiftRows = function(s, Nb) {
    var t = new Array(4);
    for (var r=1; r<4; r++) {
        for (var c=0; c<4; c++) t[c] = s[r][(c+r)%Nb];  // shift into temp copy
        for (var c=0; c<4; c++) s[r][c] = t[c];         // and copy back
    }          // note that this will work for Nb=4,5,6, but not 7,8 (always 4 for AES):
    return s;  // see asmaes.sourceforge.net/rijndael/rijndaelImplementation.pdf
};


/**
 * Combine bytes of each col of state S [§5.1.3]
 * @private
 */
Aes.mixColumns = function(s, Nb) {
    for (var c=0; c<4; c++) {
        var a = new Array(4);  // 'a' is a copy of the current column from 's'
        var b = new Array(4);  // 'b' is a•{02} in GF(2^8)
        for (var i=0; i<4; i++) {
            a[i] = s[i][c];
            b[i] = s[i][c]&0x80 ? s[i][c]<<1 ^ 0x011b : s[i][c]<<1;
        }
        // a[n] ^ b[n] is a•{03} in GF(2^8)
        s[0][c] = b[0] ^ a[1] ^ b[1] ^ a[2] ^ a[3]; // {02}•a0 + {03}•a1 + a2 + a3
        s[1][c] = a[0] ^ b[1] ^ a[2] ^ b[2] ^ a[3]; // a0 • {02}•a1 + {03}•a2 + a3
        s[2][c] = a[0] ^ a[1] ^ b[2] ^ a[3] ^ b[3]; // a0 + a1 + {02}•a2 + {03}•a3
        s[3][c] = a[0] ^ b[0] ^ a[1] ^ a[2] ^ b[3]; // {03}•a0 + a1 + a2 + {02}•a3
    }
    return s;
};


/**
 * Xor Round Key into state S [§5.1.4]
 * @private
 */
Aes.addRoundKey = function(state, w, rnd, Nb) {
    for (var r=0; r<4; r++) {
        for (var c=0; c<Nb; c++) state[r][c] ^= w[rnd*4+c][r];
    }
    return state;
};


/**
 * Apply SBox to 4-byte word w
 * @private
 */
Aes.subWord = function(w) {
    for (var i=0; i<4; i++) w[i] = Aes.sBox[w[i]];
    return w;
};


/**
 * Rotate 4-byte word w left by one byte
 * @private
 */
Aes.rotWord = function(w) {
    var tmp = w[0];
    for (var i=0; i<3; i++) w[i] = w[i+1];
    w[3] = tmp;
    return w;
};


// sBox is pre-computed multiplicative inverse in GF(2^8) used in subBytes and keyExpansion [§5.1.1]
Aes.sBox = [ 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 ];


// rCon is Round Constant used for the Key Expansion [1st col is 2^(r-1) in GF(2^8)] [§5.2]
Aes.rCon = [ [ 0x00, 0x00, 0x00, 0x00 ],
             [ 0x01, 0x00, 0x00, 0x00 ],
             [ 0x02, 0x00, 0x00, 0x00 ],
             [ 0x04, 0x00, 0x00, 0x00 ],
             [ 0x08, 0x00, 0x00, 0x00 ],
             [ 0x10, 0x00, 0x00, 0x00 ],
             [ 0x20, 0x00, 0x00, 0x00 ],
             [ 0x40, 0x00, 0x00, 0x00 ],
             [ 0x80, 0x00, 0x00, 0x00 ],
             [ 0x1b, 0x00, 0x00, 0x00 ],
             [ 0x36, 0x00, 0x00, 0x00 ] ];


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
if (typeof module != 'undefined' && module.exports) module.exports = Aes; // ≡ export default Aes
