text: /*! @license ©2015 Ruben Verborgh - Multimedia Lab / iMinds / Ghent University */
  /** Browser replacement for a subset of crypto. */
  
  exports.createHash = function () {
    var contents;
    return {
      update: function (c) { contents ? (contents += c) : (contents = c); },
      digest: function ()  { return sha1(contents); },
    };
  };
  
  /*! @license SHA-1 implementation ©2002-2014 Chris Veness / MIT Licence */
  
  /**
   * Generates SHA-1 hash of string.
   *
   * @param   {string} msg - (Unicode) string to be hashed.
   * @returns {string} Hash of msg as hex character string.
   */
  function sha1(msg) {
    // constants [§4.2.1]
    var K = [ 0x5a827999, 0x6ed9eba1, 0x8f1bbcdc, 0xca62c1d6 ];
  
    // PREPROCESSING
  
    msg += String.fromCharCode(0x80);  // add trailing '1' bit (+ 0's padding) to string [§5.1.1]
  
    // convert string msg into 512-bit/16-integer blocks arrays of ints [§5.2.1]
    var l = msg.length / 4 + 2; // length (in 32-bit integers) of msg + ‘1’ + appended length
    var N = Math.ceil(l / 16);  // number of 16-integer-blocks required to hold 'l' ints
    var M = new Array(N);
  
    for (var i = 0; i < N; i++) {
      M[i] = new Array(16);
      for (var j = 0; j < 16; j++) {  // encode 4 chars per integer, big-endian encoding
        M[i][j] = (msg.charCodeAt(i * 64 + j * 4)     << 24) |
                  (msg.charCodeAt(i * 64 + j * 4 + 1) << 16) |
                  (msg.charCodeAt(i * 64 + j * 4 + 2) << 8)  |
                  (msg.charCodeAt(i * 64 + j * 4 + 3));
      } // note running off the end of msg is ok 'cos bitwise ops on NaN return 0
    }
    // add length (in bits) into final pair of 32-bit integers (big-endian) [§5.1.1]
    // note: most significant word would be (len-1)*8 >>> 32, but since JS converts
    // bitwise-op args to 32 bits, we need to simulate this by arithmetic operators
    M[N - 1][14] = ((msg.length - 1) * 8) / Math.pow(2, 32);
    M[N - 1][14] = Math.floor(M[N - 1][14]);
    M[N - 1][15] = ((msg.length - 1) * 8) & 0xffffffff;
  
    // set initial hash value [§5.3.1]
    var H0 = 0x67452301;
    var H1 = 0xefcdab89;
    var H2 = 0x98badcfe;
    var H3 = 0x10325476;
    var H4 = 0xc3d2e1f0;
  
    // HASH COMPUTATION [§6.1.2]
  
    var W = new Array(80), a, b, c, d, e, t;
    for (i = 0; i < N; i++) {
  
      // 1 - prepare message schedule 'W'
      for (t = 0;  t < 16; t++) W[t] = M[i][t];
      for (t = 16; t < 80; t++) W[t] = ROTL(W[t - 3] ^ W[t - 8] ^ W[t - 14] ^ W[t - 16], 1);
  
      // 2 - initialise five working variables a, b, c, d, e with previous hash value
      a = H0, b = H1, c = H2, d = H3, e = H4;
  
      // 3 - main loop
      for (t = 0; t < 80; t++) {
        var s = Math.floor(t / 20); // seq for blocks of 'f' functions and 'K' constants
        var T = (ROTL(a, 5) + f(s, b, c, d) + e + K[s] + W[t]) & 0xffffffff;
        e = d;
        d = c;
        c = ROTL(b, 30);
        b = a;
        a = T;
      }
  
      // 4 - compute the new intermediate hash value (note 'addition modulo 2^32')
      H0 = (H0 + a) & 0xffffffff;
      H1 = (H1 + b) & 0xffffffff;
      H2 = (H2 + c) & 0xffffffff;
      H3 = (H3 + d) & 0xffffffff;
      H4 = (H4 + e) & 0xffffffff;
    }
  
    return toHexStr(H0) + toHexStr(H1) + toHexStr(H2) + toHexStr(H3) + toHexStr(H4);
  }
  
  /**
   * Function 'f' [§4.1.1].
   */
  function f(s, x, y, z)  {
    switch (s) {
    case 0:
      return (x & y) ^ (~x & z);           // Ch()
    case 1:
      return  x ^ y  ^  z;                 // Parity()
    case 2:
      return (x & y) ^ (x & z) ^ (y & z);  // Maj()
    case 3:
      return  x ^ y  ^  z;                 // Parity()
    }
  }
  
  /**
   * Rotates left (circular left shift) value x by n positions [§3.2.5].
   */
  function ROTL(x, n) {
    return (x << n) | (x >>> (32 - n));
  }
  
  /**
   * Hexadecimal representation of a number.
   */
  function toHexStr(n) {
    // note can't use toString(16) as it is implementation-dependant,
    // and in IE returns signed numbers when used on full words
    var s = "", v;
    for (var i = 7; i >= 0; i--) { v = (n >>> (i * 4)) & 0xf; s += v.toString(16); }
    return s;
  }
  