// OpenPGP.js - An OpenPGP implementation in javascript
// Copyright (C) 2018 ProtonTech AG
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 3.0 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

/**
 * @fileoverview This module implements AES-OCB en/decryption.
 * @requires crypto/cipher
 * @requires util
 * @module crypto/ocb
 */

import ciphers from './cipher';
import util from '../util';


const blockLength = 16;
const ivLength = 15;

// https://tools.ietf.org/html/draft-ietf-openpgp-rfc4880bis-04#section-5.16.2:
// While OCB [RFC7253] allows the authentication tag length to be of any
// number up to 128 bits long, this document requires a fixed
// authentication tag length of 128 bits (16 octets) for simplicity.
const tagLength = 16;


const { shiftLeft, shiftRight } = util;


function zeros(bytes) {
  return new Uint8Array(bytes);
}

function ntz(n) {
  let ntz = 0;
  for(let i = 1; (n & i) === 0; i <<= 1) {
    ntz++;
  }
  return ntz;
}

function set_xor(S, T) {
  for (let i = 0; i < S.length; i++) {
    S[i] ^= T[i];
  }
  return S;
}

function xor(S, T) {
  return set_xor(S.slice(), T);
}

function concat(...arrays) {
  return util.concatUint8Array(arrays);
}

function double(S) {
  const double = S.slice();
  shiftLeft(double, 1);
  if (S[0] & 0b10000000) {
    double[15] ^= 0b10000111;
  }
  return double;
}


function constructKeyVariables(cipher, key, text, adata) {
  const aes = new ciphers[cipher](key);
  const encipher = aes.encrypt.bind(aes);
  const decipher = aes.decrypt.bind(aes);

  const L_x = encipher(zeros(16));
  const L_$ = double(L_x);
  const L = [];
  L[0] = double(L_$);

  const max_ntz = util.nbits(Math.max(text.length, adata.length) >> 4) - 1;
  for (let i = 1; i <= max_ntz; i++) {
    L[i] = double(L[i - 1]);
  }

  L.x = L_x;
  L.$ = L_$;

  return { encipher, decipher, L };
}

function hash(kv, key, adata) {
  if (!adata.length) {
    // Fast path
    return zeros(16);
  }

  const { encipher, L } = kv;

  //
  // Consider A as a sequence of 128-bit blocks
  //
  const m = adata.length >> 4;

  const offset = zeros(16);
  const sum = zeros(16);
  for (let i = 0; i < m; i++) {
    set_xor(offset, L[ntz(i + 1)]);
    set_xor(sum, encipher(xor(offset, adata)));
    adata = adata.subarray(16);
  }

  //
  // Process any final partial block; compute final hash value
  //
  if (adata.length) {
    set_xor(offset, L.x);

    const cipherInput = zeros(16);
    cipherInput.set(adata, 0);
    cipherInput[adata.length] = 0b10000000;
    set_xor(cipherInput, offset);

    set_xor(sum, encipher(cipherInput));
  }

  return sum;
}


/**
 * Encrypt plaintext input.
 * @param  {String}     cipher      The symmetric cipher algorithm to use e.g. 'aes128'
 * @param  {Uint8Array} plaintext   The cleartext input to be encrypted
 * @param  {Uint8Array} key         The encryption key
 * @param  {Uint8Array} nonce       The nonce (15 bytes)
 * @param  {Uint8Array} adata       Associated data to sign
 * @returns {Promise<Uint8Array>}    The ciphertext output
 */
async function encrypt(cipher, plaintext, key, nonce, adata) {
  //
  // Consider P as a sequence of 128-bit blocks
  //
  const m = plaintext.length >> 4;

  //
  // Key-dependent variables
  //
  const kv = constructKeyVariables(cipher, key, plaintext, adata);
  const { encipher, L } = kv;

  //
  // Nonce-dependent and per-encryption variables
  //
  // We assume here that TAGLEN mod 128 == 0 (tagLength === 16).
  const Nonce = concat(zeros(15 - nonce.length), new Uint8Array([1]), nonce);
  const bottom = Nonce[15] & 0b111111;
  Nonce[15] &= 0b11000000;
  const Ktop = encipher(Nonce);
  const Stretch = concat(Ktop, xor(Ktop.subarray(0, 8), Ktop.subarray(1, 9)));
  //    Offset_0 = Stretch[1+bottom..128+bottom]
  const offset = shiftRight(Stretch.subarray(0 + (bottom >> 3), 17 + (bottom >> 3)), 8 - (bottom & 7)).subarray(1);
  const checksum = zeros(16);

  const C = new Uint8Array(plaintext.length + tagLength);

  //
  // Process any whole blocks
  //
  let i;
  let pos = 0;
  for (i = 0; i < m; i++) {
    set_xor(offset, L[ntz(i + 1)]);
    C.set(xor(offset, encipher(xor(offset, plaintext))), pos);
    set_xor(checksum, plaintext);

    plaintext = plaintext.subarray(16);
    pos += 16;
  }

  //
  // Process any final partial block and compute raw tag
  //
  if (plaintext.length) {
    set_xor(offset, L.x);
    const Pad = encipher(offset);
    C.set(xor(plaintext, Pad), pos);

    // Checksum_* = Checksum_m xor (P_* || 1 || zeros(127-bitlen(P_*)))
    const xorInput = zeros(16);
    xorInput.set(plaintext, 0);
    xorInput[plaintext.length] = 0b10000000;
    set_xor(checksum, xorInput);
    pos += plaintext.length;
  }
  const Tag = xor(encipher(xor(xor(checksum, offset), L.$)), hash(kv, key, adata));

  //
  // Assemble ciphertext
  //
  C.set(Tag, pos);
  return C;
}


/**
 * Decrypt ciphertext input.
 * @param  {String}     cipher       The symmetric cipher algorithm to use e.g. 'aes128'
 * @param  {Uint8Array} ciphertext   The ciphertext input to be decrypted
 * @param  {Uint8Array} key          The encryption key
 * @param  {Uint8Array} nonce        The nonce (15 bytes)
 * @param  {Uint8Array} adata        Associated data to verify
 * @returns {Promise<Uint8Array>}     The plaintext output
 */
async function decrypt(cipher, ciphertext, key, nonce, adata) {
  //
  // Consider C as a sequence of 128-bit blocks
  //
  const T = ciphertext.subarray(ciphertext.length - tagLength);
  ciphertext = ciphertext.subarray(0, ciphertext.length - tagLength);
  const m = ciphertext.length >> 4;

  //
  // Key-dependent variables
  //
  const kv = constructKeyVariables(cipher, key, ciphertext, adata);
  const { encipher, decipher, L } = kv;

  //
  // Nonce-dependent and per-encryption variables
  //
  // We assume here that TAGLEN mod 128 == 0 (tagLength === 16).
  const Nonce = concat(zeros(15 - nonce.length), new Uint8Array([1]), nonce);
  const bottom = Nonce[15] & 0b111111;
  Nonce[15] &= 0b11000000;
  const Ktop = encipher(Nonce);
  const Stretch = concat(Ktop, xor(Ktop.subarray(0, 8), Ktop.subarray(1, 9)));
  //    Offset_0 = Stretch[1+bottom..128+bottom]
  const offset = shiftRight(Stretch.subarray(0 + (bottom >> 3), 17 + (bottom >> 3)), 8 - (bottom & 7)).subarray(1);
  const checksum = zeros(16);

  const P = new Uint8Array(ciphertext.length);

  //
  // Process any whole blocks
  //
  let i;
  let pos = 0;
  for (i = 0; i < m; i++) {
    set_xor(offset, L[ntz(i + 1)]);
    P.set(xor(offset, decipher(xor(offset, ciphertext))), pos);
    set_xor(checksum, P.subarray(pos));

    ciphertext = ciphertext.subarray(16);
    pos += 16;
  }

  //
  // Process any final partial block and compute raw tag
  //
  if (ciphertext.length) {
    set_xor(offset, L.x);
    const Pad = encipher(offset);
    P.set(xor(ciphertext, Pad), pos);

    // Checksum_* = Checksum_m xor (P_* || 1 || zeros(127-bitlen(P_*)))
    const xorInput = zeros(16);
    xorInput.set(P.subarray(pos), 0);
    xorInput[ciphertext.length] = 0b10000000;
    set_xor(checksum, xorInput);
    pos += ciphertext.length;
  }
  const Tag = xor(encipher(xor(xor(checksum, offset), L.$)), hash(kv, key, adata));

  //
  // Check for validity and assemble plaintext
  //
  if (!util.equalsUint8Array(Tag, T)) {
    throw new Error('Authentication tag mismatch in OCB ciphertext');
  }
  return P;
}

/**
 * Get OCB nonce as defined by {@link https://tools.ietf.org/html/draft-ietf-openpgp-rfc4880bis-04#section-5.16.2|RFC4880bis-04, section 5.16.2}.
 * @param  {Uint8Array} iv           The initialization vector (15 bytes)
 * @param  {Uint8Array} chunkIndex   The chunk index (8 bytes)
 */
function getNonce(iv, chunkIndex) {
  const nonce = iv.slice();
  for (let i = 0; i < chunkIndex.length; i++) {
    nonce[7 + i] ^= chunkIndex[i];
  }
  return nonce;
}


export default {
  blockLength,
  ivLength,
  encrypt,
  decrypt,
  getNonce
};