function sha256_hmac(key, data) {
  /*	properties	*/
  function get_hexcase()			{get_hexcase	= hexcase};
  function put_hexcase(newValue)	{hexcase		= newValue};

  function get_b64pad()			{get_b64pad		= b64pad};
  function put_b64pad(newValue)	{b64pad			= newValue};


  /*	methods	*/
  /*


  /*
   * A JavaScript implementation of the Secure Hash Algorithm, SHA-256, as defined
   * in FIPS 180-2
   * Version 2.2 Copyright Angel Marin, Paul Johnston 2000 - 2009.
   * Other contributors: Greg Holt, Andrew Kepert, Ydnar, Lostinet
   * Distributed under the BSD License
   * See http://pajhome.org.uk/crypt/md5 for details.
   * Adapted into a WSC for use in classic ASP by Daniel O'Malley
   * (based on an SHA-1 example by Erik Oosterwaal)
   * for use with the Amazon Product Advertising API
   */

  /*
   * Configurable variables
   */
  var hexcase = 1;  /* hex output format. 0 - lowercase; 1 - uppercase  */
  var b64pad  = "="; /* base-64 pad character.  */

  /*
   * Calculate the HMAC-sha256 of a key and some data (raw strings)
   */
  function rstr_hmac_sha256(key, data)
  {
    var bkey = rstr2binb(key);
    if(bkey.length > 16) bkey = binb_sha256(bkey, key.length * 8);

    var ipad = Array(16), opad = Array(16);
    for(var i = 0; i < 16; i++)
    {
      ipad[i] = bkey[i] ^ 0x36363636;
      opad[i] = bkey[i] ^ 0x5C5C5C5C;
    }

    var hash = binb_sha256(ipad.concat(rstr2binb(data)), 512 + data.length * 8);
    return binb2rstr(binb_sha256(opad.concat(hash), 512 + 256));
  }

  /*
   * Convert a raw string to a hex string
   */
  function rstr2hex(input)
  {
    try { hexcase } catch(e) { hexcase=0; }
    var hex_tab = hexcase ? "0123456789ABCDEF" : "0123456789abcdef";
    var output = "";
    var x;
    for(var i = 0; i < input.length; i++)
    {
      x = input.charCodeAt(i);
      output += hex_tab.charAt((x >>> 4) & 0x0F)
             +  hex_tab.charAt( x        & 0x0F);
    }
    return output;
  }

  /*
   * Convert a raw string to a base-64 string
   */
  function rstr2b64(input)
  {
    try { b64pad } catch(e) { b64pad=''; }
    var tab = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    var output = "";
    var len = input.length;
    for(var i = 0; i < len; i += 3)
    {
      var triplet = (input.charCodeAt(i) << 16)
                  | (i + 1 < len ? input.charCodeAt(i+1) << 8 : 0)
                  | (i + 2 < len ? input.charCodeAt(i+2)      : 0);
      for(var j = 0; j < 4; j++)
      {
        if(i * 8 + j * 6 > input.length * 8) output += b64pad;
        else output += tab.charAt((triplet >>> 6*(3-j)) & 0x3F);
      }
    }
    return output;
  }

  /*
   * Convert a raw string to an arbitrary string encoding
   */
  function rstr2any(input, encoding)
  {
    var divisor = encoding.length;
    var remainders = Array();
    var i, q, x, quotient;

    /* Convert to an array of 16-bit big-endian values, forming the dividend */
    var dividend = Array(Math.ceil(input.length / 2));
    for(i = 0; i < dividend.length; i++)
    {
      dividend[i] = (input.charCodeAt(i * 2) << 8) | input.charCodeAt(i * 2 + 1);
    }

    /*
     * Repeatedly perform a long division. The binary array forms the dividend,
     * the length of the encoding is the divisor. Once computed, the quotient
     * forms the dividend for the next step. We stop when the dividend is zero.
     * All remainders are stored for later use.
     */
    while(dividend.length > 0)
    {
      quotient = Array();
      x = 0;
      for(i = 0; i < dividend.length; i++)
      {
        x = (x << 16) + dividend[i];
        q = Math.floor(x / divisor);
        x -= q * divisor;
        if(quotient.length > 0 || q > 0)
          quotient[quotient.length] = q;
      }
      remainders[remainders.length] = x;
      dividend = quotient;
    }

    /* Convert the remainders to the output string */
    var output = "";
    for(i = remainders.length - 1; i >= 0; i--)
      output += encoding.charAt(remainders[i]);

    /* Append leading zero equivalents */
    var full_length = Math.ceil(input.length * 8 /
                                      (Math.log(encoding.length) / Math.log(2)))
    for(i = output.length; i < full_length; i++)
      output = encoding[0] + output;

    return output;
  }

  /*
   * Encode a string as utf-8.
   * For efficiency, this assumes the input is valid utf-16.
   */
  function str2rstr_utf8(input)
  {
    var output = "";
    var i = -1;
    var x, y;

    while(++i < input.length)
    {
      /* Decode utf-16 surrogate pairs */
      x = input.charCodeAt(i);
      y = i + 1 < input.length ? input.charCodeAt(i + 1) : 0;
      if(0xD800 <= x && x <= 0xDBFF && 0xDC00 <= y && y <= 0xDFFF)
      {
        x = 0x10000 + ((x & 0x03FF) << 10) + (y & 0x03FF);
        i++;
      }

      /* Encode output as utf-8 */
      if(x <= 0x7F)
        output += String.fromCharCode(x);
      else if(x <= 0x7FF)
        output += String.fromCharCode(0xC0 | ((x >>> 6 ) & 0x1F),
                                      0x80 | ( x         & 0x3F));
      else if(x <= 0xFFFF)
        output += String.fromCharCode(0xE0 | ((x >>> 12) & 0x0F),
                                      0x80 | ((x >>> 6 ) & 0x3F),
                                      0x80 | ( x         & 0x3F));
      else if(x <= 0x1FFFFF)
        output += String.fromCharCode(0xF0 | ((x >>> 18) & 0x07),
                                      0x80 | ((x >>> 12) & 0x3F),
                                      0x80 | ((x >>> 6 ) & 0x3F),
                                      0x80 | ( x         & 0x3F));
    }
    return output;
  }

  /*
   * Encode a string as utf-16
   */
  function str2rstr_utf16le(input)
  {
    var output = "";
    for(var i = 0; i < input.length; i++)
      output += String.fromCharCode( input.charCodeAt(i)        & 0xFF,
                                    (input.charCodeAt(i) >>> 8) & 0xFF);
    return output;
  }

  function str2rstr_utf16be(input)
  {
    var output = "";
    for(var i = 0; i < input.length; i++)
      output += String.fromCharCode((input.charCodeAt(i) >>> 8) & 0xFF,
                                     input.charCodeAt(i)        & 0xFF);
    return output;
  }

  /*
   * Convert a raw string to an array of big-endian words
   * Characters >255 have their high-byte silently ignored.
   */
  function rstr2binb(input)
  {
    var output = Array(input.length >> 2);
    for(var i = 0; i < output.length; i++)
      output[i] = 0;
    for(var i = 0; i < input.length * 8; i += 8)
      output[i>>5] |= (input.charCodeAt(i / 8) & 0xFF) << (24 - i % 32);
    return output;
  }

  /*
   * Convert an array of big-endian words to a string
   */
  function binb2rstr(input)
  {
    var output = "";
    for(var i = 0; i < input.length * 32; i += 8)
      output += String.fromCharCode((input[i>>5] >>> (24 - i % 32)) & 0xFF);
    return output;
  }

  /*
   * Main sha256 function, with its support functions
   */
  function sha256_S (X, n) {return ( X >>> n ) | (X << (32 - n));}
  function sha256_R (X, n) {return ( X >>> n );}
  function sha256_Ch(x, y, z) {return ((x & y) ^ ((~x) & z));}
  function sha256_Maj(x, y, z) {return ((x & y) ^ (x & z) ^ (y & z));}
  function sha256_Sigma0256(x) {return (sha256_S(x, 2) ^ sha256_S(x, 13) ^ sha256_S(x, 22));}
  function sha256_Sigma1256(x) {return (sha256_S(x, 6) ^ sha256_S(x, 11) ^ sha256_S(x, 25));}
  function sha256_Gamma0256(x) {return (sha256_S(x, 7) ^ sha256_S(x, 18) ^ sha256_R(x, 3));}
  function sha256_Gamma1256(x) {return (sha256_S(x, 17) ^ sha256_S(x, 19) ^ sha256_R(x, 10));}
  function sha256_Sigma0512(x) {return (sha256_S(x, 28) ^ sha256_S(x, 34) ^ sha256_S(x, 39));}
  function sha256_Sigma1512(x) {return (sha256_S(x, 14) ^ sha256_S(x, 18) ^ sha256_S(x, 41));}
  function sha256_Gamma0512(x) {return (sha256_S(x, 1)  ^ sha256_S(x, 8) ^ sha256_R(x, 7));}
  function sha256_Gamma1512(x) {return (sha256_S(x, 19) ^ sha256_S(x, 61) ^ sha256_R(x, 6));}

  var sha256_K = new Array
  (
    1116352408, 1899447441, -1245643825, -373957723, 961987163, 1508970993,
    -1841331548, -1424204075, -670586216, 310598401, 607225278, 1426881987,
    1925078388, -2132889090, -1680079193, -1046744716, -459576895, -272742522,
    264347078, 604807628, 770255983, 1249150122, 1555081692, 1996064986,
    -1740746414, -1473132947, -1341970488, -1084653625, -958395405, -710438585,
    113926993, 338241895, 666307205, 773529912, 1294757372, 1396182291,
    1695183700, 1986661051, -2117940946, -1838011259, -1564481375, -1474664885,
    -1035236496, -949202525, -778901479, -694614492, -200395387, 275423344,
    430227734, 506948616, 659060556, 883997877, 958139571, 1322822218,
    1537002063, 1747873779, 1955562222, 2024104815, -2067236844, -1933114872,
    -1866530822, -1538233109, -1090935817, -965641998
  );

  function binb_sha256(m, l)
  {
    var HASH = new Array(1779033703, -1150833019, 1013904242, -1521486534,
                         1359893119, -1694144372, 528734635, 1541459225);
    var W = new Array(64);
    var a, b, c, d, e, f, g, h;
    var i, j, T1, T2;

    /* append padding */
    m[l >> 5] |= 0x80 << (24 - l % 32);
    m[((l + 64 >> 9) << 4) + 15] = l;

    for(i = 0; i < m.length; i += 16)
    {
      a = HASH[0];
      b = HASH[1];
      c = HASH[2];
      d = HASH[3];
      e = HASH[4];
      f = HASH[5];
      g = HASH[6];
      h = HASH[7];

      for(j = 0; j < 64; j++)
      {
        if (j < 16) W[j] = m[j + i];
        else W[j] = safe_add(safe_add(safe_add(sha256_Gamma1256(W[j - 2]), W[j - 7]),
                                              sha256_Gamma0256(W[j - 15])), W[j - 16]);

        T1 = safe_add(safe_add(safe_add(safe_add(h, sha256_Sigma1256(e)), sha256_Ch(e, f, g)),
                                                            sha256_K[j]), W[j]);
        T2 = safe_add(sha256_Sigma0256(a), sha256_Maj(a, b, c));
        h = g;
        g = f;
        f = e;
        e = safe_add(d, T1);
        d = c;
        c = b;
        b = a;
        a = safe_add(T1, T2);
      }

      HASH[0] = safe_add(a, HASH[0]);
      HASH[1] = safe_add(b, HASH[1]);
      HASH[2] = safe_add(c, HASH[2]);
      HASH[3] = safe_add(d, HASH[3]);
      HASH[4] = safe_add(e, HASH[4]);
      HASH[5] = safe_add(f, HASH[5]);
      HASH[6] = safe_add(g, HASH[6]);
      HASH[7] = safe_add(h, HASH[7]);
    }
    return HASH;
  }

  function safe_add (x, y)
  {
    var lsw = (x & 0xFFFF) + (y & 0xFFFF);
    var msw = (x >> 16) + (y >> 16) + (lsw >> 16);
    return (msw << 16) | (lsw & 0xFFFF);
  }

  return rstr2hex(rstr_hmac_sha256(key, data)).toLowerCase();
}