aes.js

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
/* AES implementation in JavaScript                                   (c) Chris Veness 2005-2019  */
/*                                                                                   MIT Licence  */
/* www.movable-type.co.uk/scripts/aes.html                                                        */
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */


/**
 * AES (Rijndael cipher) encryption routines reference implementation,
 *
 * This is an annotated direct implementation of FIPS 197, without any optimisations. It is
 * intended to aid understanding of the algorithm rather than for production use.
 *
 * While it could be used where performance is not critical, I would recommend using the ‘Web
 * Cryptography API’ (developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto/encrypt) for the browser,
 * or the ‘crypto’ library (nodejs.org/api/crypto.html#crypto_class_cipher) in Node.js.
 *
 * See csrc.nist.gov/publications/fips/fips197/fips-197.pdf
 */
class 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 × Nb bytes).
     * @returns {number[]}   Encrypted output state array.
     */
    static cipher(input, w) {
        const Nb = 4;               // block size (in words): no of columns in state (fixed at 4 for AES)
        const Nr = w.length/Nb - 1; // no of rounds: 10/12/14 for 128/192/256-bit keys

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

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

        for (let 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);

        const output = new Array(4*Nb);  // convert state to 1-d array before returning [§3.4]
        for (let 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 × Nb bytes).
     */
    static keyExpansion(key) {
        const Nb = 4;            // block size (in words): no of columns in state (fixed at 4 for AES)
        const Nk = key.length/4; // key length (in words): 4/6/8 for 128/192/256-bit keys
        const Nr = Nk + 6;       // no of rounds: 10/12/14 for 128/192/256-bit keys

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

        // initialise first Nk words of expanded key with cipher key
        for (let i=0; i<Nk; i++) {
            const 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 (let i=Nk; i<(Nb*(Nr+1)); i++) {
            w[i] = new Array(4);
            for (let 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 (let 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 (let 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
     */
    static subBytes(s, Nb) {
        for (let r=0; r<4; r++) {
            for (let 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
     */
    static shiftRows(s, Nb) {
        const t = new Array(4);
        for (let r=1; r<4; r++) {
            for (let c=0; c<4; c++) t[c] = s[r][(c+r)%Nb];  // shift into temp copy
            for (let 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
     */
    static mixColumns(s, Nb) {
        for (let c=0; c<Nb; c++) {
            const a = new Array(Nb);  // 'a' is a copy of the current column from 's'
            const b = new Array(Nb);  // 'b' is a•{02} in GF(2^8)
            for (let r=0; r<4; r++) {
                a[r] = s[r][c];
                b[r] = s[r][c]&0x80 ? s[r][c]<<1 ^ 0x011b : s[r][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
     */
    static addRoundKey(state, w, rnd, Nb) {
        for (let r=0; r<4; r++) {
            for (let c=0; c<Nb; c++) state[r][c] ^= w[rnd*4+c][r];
        }
        return state;
    }


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


    /**
     * Rotate 4-byte word w left by one byte.
     *
     * @private
     */
    static rotWord(w) {
        const tmp = w[0];
        for (let 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 ],
];


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */

export default Aes;