/**
 * @preserve Copyright (c) 2014-2015 IONU Security, Inc. All rights reserved.
 * 
 * @file EyeDRBG methods for deterministic random bit generation and predictable RSA keys
 */


IONU_DRBG_BUFFER_LEN  = 32768;

if(typeof BigInteger === 'undefined') {
  var BigInteger = forge.jsbn.BigInteger;
}

/**
 * Constructor for DRBG object
 * @constructor
 * @param {string} seed value
 */
function EyeDRBG (seed) {
  if (!(this instanceof EyeDRBG)){
    return new EyeDRBG (seed);
  }
  this.seed = seed;
  this.ctr = seed.length & 255;
  this.buffer = '';
  this.pos = 0;
  var md = forge.md.sha256.create();
  md.update(seed);
  this.hashbuf = md.digest().getBytes();
  //console.log (forge.util.bytesToHex(this.hashbuf));
}

// Define methods for EyeDRBG object
EyeDRBG.prototype = {
  constructor: EyeDRBG,

  /**
   * Fill the buffer with pseudo random bytes
   * @private
   */
  fillBuffer: function() {
    const BUFF_SIZE = IONU_DRBG_BUFFER_LEN;
    this.buffer = '';
    this.pos = 0;
    var msg = '';
    var md = forge.md.sha256.create();
    for (var i = 0; i < BUFF_SIZE; i += 32) {
      msg = '';
      md.start();
      for (var j = 0; j < 32; ++j) {
         msg += String.fromCharCode (this.hashbuf.charCodeAt(j));
      }
      msg += String.fromCharCode(this.ctr++ & 255);
      md.update(msg);
      this.hashbuf = md.digest().getBytes();
      this.buffer += this.hashbuf;
      //console.log (forge.util.bytesToHex(this.hashbuf));
    }
  },

  /**
   * Get the specifed number of bytes
   * @param {number} count bytes to get
   * @return {string} byte string
   */
  randBytes: function (count) {
    var bytes = '';
    var bytesavailable = this.buffer.length - this.pos;
    // We have all the bytes needed
    if (bytesavailable >= count) {
      bytes = this.buffer.slice(this.pos, this.pos + count);
      this.pos += count;
    }
    else {
      // Copy any remaining bytes
      if (bytesavailable > 0) {
        count -= bytesavailable;
        bytes = this.buffer.slice (this.pos, bytesavailable);
      }
      // Loop until we've generated all the required bytes
      while (count > 0) {
        this.fillBuffer ();
        bytesavailable = this.buffer.length - this.pos;
        if (bytesavailable >= count ) {
          bytes += this.buffer.slice(this.pos, this.pos + count);
          this.pos += count;
          count = 0;
        }
        else {
          count -= bytesavailable;
          bytes += this.buffer.slice (this.pos, bytesavailable);
        }
      }
    }
    return bytes;
  },

  /**
   * Get an integer with the specifed number of bits
   * @param {number} bits number of bits to get
   * @return {number} integer of specified number of bits
   */
  randBits: function (bits) {
    var rval = 0;
    var numBytes = Math.floor ((bits + 7) / 8);

    for (i = 0; i < numBytes; i++) {
      rval = (rval << 8) | this.randBytes (1);
    }
    return rval & (1 << bits);
  },

  /**
   * Get an integer from 0 to the specifed maximum
   * @param {number} maximum largest integer to get
   * @return {number} integer between 0 and maximum, inclusive
   */
  randInteger: function (maximum) {
    var n = 1, numBits = 0;

    //  numBits = log_2 n, where n >= maximum
    while (maximum >= n) {
      if (numBits > 0) {
        n <<= 1;
      }
      numBits++;
    }

    // Generate random values from 0 through n, then discard any values where value > maximum.
    // See Ferguson and Schneier, "Practical Cryptography" for why this is better than using mod
    while (true) {
      var value = this.randBits (numBits);
      if (value <= n) {
        return value;
      }
    }
  },

  /**
   * Generate pseudo prime suitable for RSA key
   * @param {BigInteger} exponent public exponent (65,537)
   * @return {BigInteger} prime number
   */
  generateRSAPrime: function (e) {
    // Only works for IONU_RSA_KEY_BITS size keys, prime is IONU_RSA_KEY_BITS / 2
    var bytes = IONU_RSA_KEY_BITS / 16;
    var op_or = function(x,y) { return x|y; };
    var THIRTY = new BigInteger(null);
    THIRTY.fromInt(30);
    var iterations = 0;
    while (true) {
      buff = this.randBytes (bytes); // Get bytes from our DRBG
      var hex = forge.util.bytesToHex(buff);
      var prime = new BigInteger (hex, 16);

      // Set 2 most significant bits so p * q is exactly n bits, and least to ensure odd
      var bits = IONU_RSA_KEY_BITS / 2 - 1;
      prime.bitwiseTo (BigInteger.ONE.shiftLeft(bits), op_or, prime);
      prime.bitwiseTo (BigInteger.ONE.shiftLeft(bits-1), op_or, prime);
      prime.bitwiseTo (BigInteger.ONE, op_or, prime);
      if (++iterations >= 2000) {
        console.log ('prime failed in 2000 iterations');
        return prime;
      }
      // Ensure number is coprime with e
      if (prime.subtract(BigInteger.ONE).gcd(e).compareTo(BigInteger.ONE) === 0) {
        // Check to see if it is prime
        if (prime.isProbablePrime(2)) {
          //console.log ('prime in ' + iterations + ' iterations');
          return prime;
        }
      }
    }
  },

  /**
   * Generate deterministic RSA key
   * @return {Key}
   */
  generateRSAKey: function () {
    // Set up public exponent
    var eInt = IONU_RSA_PUBLIC_EXP;
    var e = new BigInteger(null);
    e.fromInt(eInt);

    // Generate random primes suitable for RSA keys, proper size, odd numbers and
    // checking for coprime with e is done in generateRSAPrime.
    var p = this.generateRSAPrime (e);
    var q = this.generateRSAPrime (e);
    while (p.compareTo (q) === 0) { // Just is case they are equal
      q = this.generateRSAPrime (e);
      if (p.compareTo (q) === 0) {  // Equal again, it's a bug, don't hang
        console.log ('generateRSAKey() - generated the same p and q');
        return undefined;
      }
    }

    // Ensure p is larger than q (swap them if not for performance)
    if(p.compareTo(q) < 0) {
      var num = p;
      p = q;
      q = num;
    }
    // Compute phi: (p - 1)(q - 1) (Euler's totient function)
    var p1 = p.subtract(BigInteger.ONE);
    var q1 = q.subtract(BigInteger.ONE);
    var phi = p1.multiply(q1);

    // Ensure e and phi are coprime, ignore this test as OpenSSL does not use it
    if(phi.gcd(e).compareTo(BigInteger.ONE) !== 0) {
      console.log ('generateRSAKey() - phi and e are not coprime');
    }

    // Create n, and ensure it has the right number of bits
    var n = p.multiply(q);
    if (n.bitLength() !== IONU_RSA_KEY_BITS) {
      console.log ('generateRSAKey() - invalid bit length ' + n.bitLength());
      return undefined;
    }
    // set keys
    var d = e.modInverse(phi);
    var key = {
      privateKey: forge.pki.rsa.setPrivateKey (n, e, d, p, q, d.mod(p1), d.mod(q1), q.modInverse(p)),
      publicKey:  forge.pki.rsa.setPublicKey (n, e)
    };
    return key;
  }
};