bintzwing/core/bn.js

/**
 * Constructs a new bignum from another bignum, a number or a hex string.
 */
sjcl.bn = function(it) {
  this.initWith(it);
};

sjcl.bn.prototype = {
  radix: 24,
  maxMul: 8,
  _class: sjcl.bn,
  
  copy: function() {
    return new this._class(this);
  },

  /**
   * Initializes this with it, either as a bn, a number, or a hex string.
   */
  initWith: function(it) {
    var i=0, k, n, l;
    switch(typeof it) {
    case "object":
      this.limbs = it.limbs.slice(0);
      break;
      
    case "number":
      this.limbs = [it];
      this.normalize();
      break;
      
    case "string":
      it = it.replace(/^0x/, '');
      this.limbs = [];
      // hack
      k = this.radix / 4;
      for (i=0; i < it.length; i+=k) {
        this.limbs.push(parseInt(it.substring(Math.max(it.length - i - k, 0), it.length - i),16));
      }
      break;

    default:
      this.limbs = [0];
    }
    return this;
  },

  /**
   * Returns true if "this" and "that" are equal.  Calls fullReduce().
   * Equality test is in constant time.
   */
  equals: function(that) {
    if (typeof that === "number") { that = new this._class(that); }
    var difference = 0, i;
    this.fullReduce();
    that.fullReduce();
    for (i = 0; i < this.limbs.length || i < that.limbs.length; i++) {
      difference |= this.getLimb(i) ^ that.getLimb(i);
    }
    return (difference === 0);
  },
  
  /**
   * Get the i'th limb of this, zero if i is too large.
   */
  getLimb: function(i) {
    return (i >= this.limbs.length) ? 0 : this.limbs[i];
  },
  
  /**
   * Constant time comparison function.
   * Returns 1 if this >= that, or zero otherwise.
   */
  greaterEquals: function(that) {
    if (typeof that === "number") { that = new this._class(that); }
    var less = 0, greater = 0, i, a, b;
    i = Math.max(this.limbs.length, that.limbs.length) - 1;
    for (; i>= 0; i--) {
      a = this.getLimb(i);
      b = that.getLimb(i);
      greater |= (b - a) & ~less;
      less |= (a - b) & ~greater;
    }
    return (greater | ~less) >>> 31;
  },
  
  /**
   * Convert to a hex string.
   */
  toString: function() {
    this.fullReduce();
    var out="", i, s, l = this.limbs;
    for (i=0; i < this.limbs.length; i++) {
      s = l[i].toString(16);
      while (i < this.limbs.length - 1 && s.length < 6) {
        s = "0" + s;
      }
      out = s + out;
    }
    return "0x"+out;
  },
  
  /** this += that.  Does not normalize. */
  addM: function(that) {
    if (typeof(that) !== "object") { that = new this._class(that); }
    var i, l=this.limbs, ll=that.limbs;
    for (i=l.length; i<ll.length; i++) {
      l[i] = 0;
    }
    for (i=0; i<ll.length; i++) {
      l[i] += ll[i];
    }
    return this;
  },
  
  /** this *= 2.  Requires normalized; ends up normalized. */
  doubleM: function() {
    var i, carry=0, tmp, r=this.radix, m=this.radixMask, l=this.limbs;
    for (i=0; i<l.length; i++) {
      tmp = l[i];
      tmp = tmp+tmp+carry;
      l[i] = tmp & m;
      carry = tmp >> r;
    }
    if (carry) {
      l.push(carry);
    }
    return this;
  },
  
  /** this /= 2, rounded down.  Requires normalized; ends up normalized. */
  halveM: function() {
    var i, carry=0, tmp, r=this.radix, l=this.limbs;
    for (i=l.length-1; i>=0; i--) {
      tmp = l[i];
      l[i] = (tmp+carry)>>1;
      carry = (tmp&1) << r;
    }
    if (!l[l.length-1]) {
      l.pop();
    }
    return this;
  },

  /** this -= that.  Does not normalize. */
  subM: function(that) {
    if (typeof(that) !== "object") { that = new this._class(that); }
    var i, l=this.limbs, ll=that.limbs;
    for (i=l.length; i<ll.length; i++) {
      l[i] = 0;
    }
    for (i=0; i<ll.length; i++) {
      l[i] -= ll[i];
    }
    return this;
  },
  
  mod: function(that) {
    that = new sjcl.bn(that).normalize(); // copy before we begin
    var out = new sjcl.bn(this).normalize(), ci=0;
    
    for (; out.greaterEquals(that); ci++) {
      that.doubleM();
    }
    for (; ci > 0; ci--) {
      that.halveM();
      if (out.greaterEquals(that)) {
        out.subM(that).normalize();
      }
    }
    return out.trim();
  },
  
  /** return inverse mod prime p.  p must be odd. Binary extended Euclidean algorithm mod p. */
  inverseMod: function(p) {
    var a = new sjcl.bn(1), b = new sjcl.bn(0), x = new sjcl.bn(this), y = new sjcl.bn(p), tmp, i, nz=1;
    
    if (!(p.limbs[0] & 1)) {
      throw (new sjcl.exception.invalid("inverseMod: p must be odd"));
    }
    
    // invariant: y is odd
    do {
      if (x.limbs[0] & 1) {
        if (!x.greaterEquals(y)) {
          // x < y; swap everything
          tmp = x; x = y; y = tmp;
          tmp = a; a = b; b = tmp;
        }
        x.subM(y);
        x.normalize();
        
        if (!a.greaterEquals(b)) {
          a.addM(p);
        }
        a.subM(b);
      }
      
      // cut everything in half
      x.halveM();
      if (a.limbs[0] & 1) {
        a.addM(p);
      }
      a.normalize();
      a.halveM();
      
      // check for termination: x ?= 0
      for (i=nz=0; i<x.limbs.length; i++) {
        nz |= x.limbs[i];
      }
    } while(nz);
    
    if (!y.equals(1)) {
      throw (new sjcl.exception.invalid("inverseMod: p and x must be relatively prime"));
    }
    
    return b;
  },
  
  /** this + that.  Does not normalize. */
  add: function(that) {
    return this.copy().addM(that);
  },

  /** this - that.  Does not normalize. */
  sub: function(that) {
    return this.copy().subM(that);
  },
  
  /** this * that.  Normalizes and reduces. */
  mul: function(that) {
    if (typeof(that) === "number") { that = new this._class(that); }
    var i, j, a = this.limbs, b = that.limbs, al = a.length, bl = b.length, out = new this._class(), c = out.limbs, ai, ii=this.maxMul;

    for (i=0; i < this.limbs.length + that.limbs.length + 1; i++) {
      c[i] = 0;
    }
    for (i=0; i<al; i++) {
      ai = a[i];
      for (j=0; j<bl; j++) {
        c[i+j] += ai * b[j];
      }
     
      if (!--ii) {
        ii = this.maxMul;
        out.cnormalize();
      }
    }
    return out.cnormalize().reduce();
  },

  /** this ^ 2.  Normalizes and reduces. */
  square: function() {
    return this.mul(this);
  },

  /** this ^ n.  Uses square-and-multiply.  Normalizes and reduces. */
  power: function(l) {
    if (typeof(l) === "number") {
      l = [l];
    } else if (l.limbs !== undefined) {
      l = l.normalize().limbs;
    }
    var i, j, out = new this._class(1), pow = this;

    for (i=0; i<l.length; i++) {
      for (j=0; j<this.radix; j++) {
        if (l[i] & (1<<j)) {
          out = out.mul(pow);
        }
        pow = pow.square();
      }
    }
    
    return out;
  },

  mulmod: function(x, N) {
    return this.mod(N).mul(x.mod(N)).mod(N);
  },

  powermod: function(x, N) {
    var result = new sjcl.bn(1), a = new sjcl.bn(this), k = new sjcl.bn(x);
    while (true) {
      if (k.limbs[0] & 1) { result = result.mulmod(a, N); }
      k.halveM();
      if (k.equals(0)) { break; }
      a = a.mulmod(a, N);
    }
    return result.normalize().reduce();
  },

  trim: function() {
    var l = this.limbs, p;
    do {
      p = l.pop();
    } while (l.length && p === 0);
    l.push(p);
    return this;
  },
  
  /** Reduce mod a modulus.  Stubbed for subclassing. */
  reduce: function() {
    return this;
  },

  /** Reduce and normalize. */
  fullReduce: function() {
    return this.normalize();
  },
  
  /** Propagate carries. */
  normalize: function() {
    var carry=0, i, pv = this.placeVal, ipv = this.ipv, l, m, limbs = this.limbs, ll = limbs.length, mask = this.radixMask;
    for (i=0; i < ll || (carry !== 0 && carry !== -1); i++) {
      l = (limbs[i]||0) + carry;
      m = limbs[i] = l & mask;
      carry = (l-m)*ipv;
    }
    if (carry === -1) {
      limbs[i-1] -= this.placeVal;
    }
    return this;
  },

  /** Constant-time normalize. Does not allocate additional space. */
  cnormalize: function() {
    var carry=0, i, ipv = this.ipv, l, m, limbs = this.limbs, ll = limbs.length, mask = this.radixMask;
    for (i=0; i < ll-1; i++) {
      l = limbs[i] + carry;
      m = limbs[i] = l & mask;
      carry = (l-m)*ipv;
    }
    limbs[i] += carry;
    return this;
  },
  
  /** Serialize to a bit array */
  toBits: function(len) {
    this.fullReduce();
    len = len || this.exponent || this.limbs.length * this.radix;
    var i = Math.floor((len-1)/24), w=sjcl.bitArray, e = (len + 7 & -8) % this.radix || this.radix,
        out = [w.partial(e, this.getLimb(i))];
    for (i--; i >= 0; i--) {
      out = w.concat(out, [w.partial(this.radix, this.getLimb(i))]);
    }
    return out;
  },
  
  /** Return the length in bits, rounded up to the nearest byte. */
  bitLength: function() {
    this.fullReduce();
    var out = this.radix * (this.limbs.length - 1),
        b = this.limbs[this.limbs.length - 1];
    for (; b; b >>= 1) {
      out ++;
    }
    return out+7 & -8;
  }
};

sjcl.bn.fromBits = function(bits) {
  var Class = this, out = new Class(), words=[], w=sjcl.bitArray, t = this.prototype,
      l = Math.min(this.bitLength || 0x100000000, w.bitLength(bits)), e = l % t.radix || t.radix;
  
  words[0] = w.extract(bits, 0, e);
  for (; e < l; e += t.radix) {
    words.unshift(w.extract(bits, e, t.radix));
  }

  out.limbs = words;
  return out;
};



sjcl.bn.prototype.ipv = 1 / (sjcl.bn.prototype.placeVal = Math.pow(2,sjcl.bn.prototype.radix));
sjcl.bn.prototype.radixMask = (1 << sjcl.bn.prototype.radix) - 1;

/**
 * Creates a new subclass of bn, based on reduction modulo a pseudo-Mersenne prime,
 * i.e. a prime of the form 2^e + sum(a * 2^b),where the sum is negative and sparse.
 */
sjcl.bn.pseudoMersennePrime = function(exponent, coeff) {
  function p(it) {
    this.initWith(it);
    /*if (this.limbs[this.modOffset]) {
      this.reduce();
    }*/
  }

  var ppr = p.prototype = new sjcl.bn(), i, tmp, mo;
  mo = ppr.modOffset = Math.ceil(tmp = exponent / ppr.radix);
  ppr.exponent = exponent;
  ppr.offset = [];
  ppr.factor = [];
  ppr.minOffset = mo;
  ppr.fullMask = 0;
  ppr.fullOffset = [];
  ppr.fullFactor = [];
  ppr.modulus = p.modulus = new sjcl.bn(Math.pow(2,exponent));
  
  ppr.fullMask = 0|-Math.pow(2, exponent % ppr.radix);

  for (i=0; i<coeff.length; i++) {
    ppr.offset[i] = Math.floor(coeff[i][0] / ppr.radix - tmp);
    ppr.fullOffset[i] = Math.ceil(coeff[i][0] / ppr.radix - tmp);
    ppr.factor[i] = coeff[i][1] * Math.pow(1/2, exponent - coeff[i][0] + ppr.offset[i] * ppr.radix);
    ppr.fullFactor[i] = coeff[i][1] * Math.pow(1/2, exponent - coeff[i][0] + ppr.fullOffset[i] * ppr.radix);
    ppr.modulus.addM(new sjcl.bn(Math.pow(2,coeff[i][0])*coeff[i][1]));
    ppr.minOffset = Math.min(ppr.minOffset, -ppr.offset[i]); // conservative
  }
  ppr._class = p;
  ppr.modulus.cnormalize();

  /** Approximate reduction mod p.  May leave a number which is negative or slightly larger than p. */
  ppr.reduce = function() {
    var i, k, l, mo = this.modOffset, limbs = this.limbs, aff, off = this.offset, ol = this.offset.length, fac = this.factor, ll;

    i = this.minOffset;
    while (limbs.length > mo) {
      l = limbs.pop();
      ll = limbs.length;
      for (k=0; k<ol; k++) {
        limbs[ll+off[k]] -= fac[k] * l;
      }
      
      i--;
      if (!i) {
        limbs.push(0);
        this.cnormalize();
        i = this.minOffset;
      }
    }
    this.cnormalize();

    return this;
  };
  
  ppr._strongReduce = (ppr.fullMask === -1) ? ppr.reduce : function() {
    var limbs = this.limbs, i = limbs.length - 1, k, l;
    this.reduce();
    if (i === this.modOffset - 1) {
      l = limbs[i] & this.fullMask;
      limbs[i] -= l;
      for (k=0; k<this.fullOffset.length; k++) {
        limbs[i+this.fullOffset[k]] -= this.fullFactor[k] * l;
      }
      this.normalize();
    }
  };

  /** mostly constant-time, very expensive full reduction. */
  ppr.fullReduce = function() {
    var greater, i;
    // massively above the modulus, may be negative
    
    this._strongReduce();
    // less than twice the modulus, may be negative

    this.addM(this.modulus);
    this.addM(this.modulus);
    this.normalize();
    // probably 2-3x the modulus
    
    this._strongReduce();
    // less than the power of 2.  still may be more than
    // the modulus

    // HACK: pad out to this length
    for (i=this.limbs.length; i<this.modOffset; i++) {
      this.limbs[i] = 0;
    }
    
    // constant-time subtract modulus
    greater = this.greaterEquals(this.modulus);
    for (i=0; i<this.limbs.length; i++) {
      this.limbs[i] -= this.modulus.limbs[i] * greater;
    }
    this.cnormalize();

    return this;
  };

  ppr.inverse = function() {
    return (this.power(this.modulus.sub(2)));
  };

  p.fromBits = sjcl.bn.fromBits;

  return p;
};

// a small Mersenne prime
sjcl.bn.prime = {
  p127: sjcl.bn.pseudoMersennePrime(127, [[0,-1]]),

  // Bernstein's prime for Curve25519
  p25519: sjcl.bn.pseudoMersennePrime(255, [[0,-19]]),

  // NIST primes
  p192: sjcl.bn.pseudoMersennePrime(192, [[0,-1],[64,-1]]),
  p224: sjcl.bn.pseudoMersennePrime(224, [[0,1],[96,-1]]),
  p256: sjcl.bn.pseudoMersennePrime(256, [[0,-1],[96,1],[192,1],[224,-1]]),
  p384: sjcl.bn.pseudoMersennePrime(384, [[0,-1],[32,1],[96,-1],[128,-1]]),
  p521: sjcl.bn.pseudoMersennePrime(521, [[0,-1]])
};

sjcl.bn.random = function(modulus, paranoia) {
  if (typeof modulus !== "object") { modulus = new sjcl.bn(modulus); }
  var words, i, l = modulus.limbs.length, m = modulus.limbs[l-1]+1, out = new sjcl.bn();
  while (true) {
    // get a sequence whose first digits make sense
    do {
      words = sjcl.random.randomWords(l, paranoia);
      if (words[l-1] < 0) { words[l-1] += 0x100000000; }
    } while (Math.floor(words[l-1] / m) === Math.floor(0x100000000 / m));
    words[l-1] %= m;

    // mask off all the limbs
    for (i=0; i<l-1; i++) {
      words[i] &= modulus.radixMask;
    }

    // check the rest of the digitssj
    out.limbs = words;
    if (!out.greaterEquals(modulus)) {
      return out;
    }
  }
};