bintzwing/core/ocb2.js

/** @fileOverview OCB 2.0 implementation
 *
 * @author Emily Stark
 * @author Mike Hamburg
 * @author Dan Boneh
 */

/** @namespace
 * Phil Rogaway's Offset CodeBook mode, version 2.0.
 * May be covered by US and international patents.
 *
 * @author Emily Stark
 * @author Mike Hamburg
 * @author Dan Boneh
 */
sjcl.mode.ocb2 = {
  /** The name of the mode.
   * @constant
   */
  name: "ocb2",
  
  /** Encrypt in OCB mode, version 2.0.
   * @param {Object} prp The block cipher.  It must have a block size of 16 bytes.
   * @param {bitArray} plaintext The plaintext data.
   * @param {bitArray} iv The initialization value.
   * @param {bitArray} [adata=[]] The authenticated data.
   * @param {Number} [tlen=64] the desired tag length, in bits.
   * @param [false] premac 1 if the authentication data is pre-macced with PMAC.
   * @return The encrypted data, an array of bytes.
   * @throws {sjcl.exception.invalid} if the IV isn't exactly 128 bits.
   */
  encrypt: function(prp, plaintext, iv, adata, tlen, premac) {
    if (sjcl.bitArray.bitLength(iv) !== 128) {
      throw new sjcl.exception.invalid("ocb iv must be 128 bits");
    }
    var i,
        times2 = sjcl.mode.ocb2._times2,
        w = sjcl.bitArray,
        xor = w._xor4,
        checksum = [0,0,0,0],
        delta = times2(prp.encrypt(iv)),
        bi, bl,
        output = [],
        pad;
        
    adata = adata || [];
    tlen  = tlen || 64;
  
    for (i=0; i+4 < plaintext.length; i+=4) {
      /* Encrypt a non-final block */
      bi = plaintext.slice(i,i+4);
      checksum = xor(checksum, bi);
      output = output.concat(xor(delta,prp.encrypt(xor(delta, bi))));
      delta = times2(delta);
    }
    
    /* Chop out the final block */
    bi = plaintext.slice(i);
    bl = w.bitLength(bi);
    pad = prp.encrypt(xor(delta,[0,0,0,bl]));
    bi = w.clamp(xor(bi.concat([0,0,0]),pad), bl);
    
    /* Checksum the final block, and finalize the checksum */
    checksum = xor(checksum,xor(bi.concat([0,0,0]),pad));
    checksum = prp.encrypt(xor(checksum,xor(delta,times2(delta))));
    
    /* MAC the header */
    if (adata.length) {
      checksum = xor(checksum, premac ? adata : sjcl.mode.ocb2.pmac(prp, adata));
    }
    
    return output.concat(w.concat(bi, w.clamp(checksum, tlen)));
  },
  
  /** Decrypt in OCB mode.
   * @param {Object} prp The block cipher.  It must have a block size of 16 bytes.
   * @param {bitArray} ciphertext The ciphertext data.
   * @param {bitArray} iv The initialization value.
   * @param {bitArray} [adata=[]] The authenticated data.
   * @param {Number} [tlen=64] the desired tag length, in bits.
   * @param {boolean} [premac=false] true if the authentication data is pre-macced with PMAC.
   * @return The decrypted data, an array of bytes.
   * @throws {sjcl.exception.invalid} if the IV isn't exactly 128 bits.
   * @throws {sjcl.exception.corrupt} if if the message is corrupt.
   */
  decrypt: function(prp, ciphertext, iv, adata, tlen, premac) {
    if (sjcl.bitArray.bitLength(iv) !== 128) {
      throw new sjcl.exception.invalid("ocb iv must be 128 bits");
    }
    tlen  = tlen || 64;
    var i,
        times2 = sjcl.mode.ocb2._times2,
        w = sjcl.bitArray,
        xor = w._xor4,
        checksum = [0,0,0,0],
        delta = times2(prp.encrypt(iv)),
        bi, bl,
        len = sjcl.bitArray.bitLength(ciphertext) - tlen,
        output = [],
        pad;
        
    adata = adata || [];
  
    for (i=0; i+4 < len/32; i+=4) {
      /* Decrypt a non-final block */
      bi = xor(delta, prp.decrypt(xor(delta, ciphertext.slice(i,i+4))));
      checksum = xor(checksum, bi);
      output = output.concat(bi);
      delta = times2(delta);
    }
    
    /* Chop out and decrypt the final block */
    bl = len-i*32;
    pad = prp.encrypt(xor(delta,[0,0,0,bl]));
    bi = xor(pad, w.clamp(ciphertext.slice(i),bl).concat([0,0,0]));
    
    /* Checksum the final block, and finalize the checksum */
    checksum = xor(checksum, bi);
    checksum = prp.encrypt(xor(checksum, xor(delta, times2(delta))));
    
    /* MAC the header */
    if (adata.length) {
      checksum = xor(checksum, premac ? adata : sjcl.mode.ocb2.pmac(prp, adata));
    }
    
    if (!w.equal(w.clamp(checksum, tlen), w.bitSlice(ciphertext, len))) {
      throw new sjcl.exception.corrupt("ocb: tag doesn't match");
    }
    
    return output.concat(w.clamp(bi,bl));
  },
  
  /** PMAC authentication for OCB associated data.
   * @param {Object} prp The block cipher.  It must have a block size of 16 bytes.
   * @param {bitArray} adata The authenticated data.
   */
  pmac: function(prp, adata) {
    var i,
        times2 = sjcl.mode.ocb2._times2,
        w = sjcl.bitArray,
        xor = w._xor4,
        checksum = [0,0,0,0],
        delta = prp.encrypt([0,0,0,0]),
        bi;
        
    delta = xor(delta,times2(times2(delta)));
 
    for (i=0; i+4<adata.length; i+=4) {
      delta = times2(delta);
      checksum = xor(checksum, prp.encrypt(xor(delta, adata.slice(i,i+4))));
    }
    
    bi = adata.slice(i);
    if (w.bitLength(bi) < 128) {
      delta = xor(delta,times2(delta));
      bi = w.concat(bi,[0x80000000|0,0,0,0]);
    }
    checksum = xor(checksum, bi);
    return prp.encrypt(xor(times2(xor(delta,times2(delta))), checksum));
  },
  
  /** Double a block of words, OCB style.
   * @private
   */
  _times2: function(x) {
    return [x[0]<<1 ^ x[1]>>>31,
            x[1]<<1 ^ x[2]>>>31,
            x[2]<<1 ^ x[3]>>>31,
            x[3]<<1 ^ (x[0]>>>31)*0x87];
  }
};