// =========================================================================
// SHA-1 Cryptographic Hash Algorithm
// (C) 2002-2005 Chris Veness
// http://www.movable-type.co.uk/scripts/SHA-1.html
// =========================================================================

function SHA1Encode(msg)
{
    // constants [4.2.1]
    var K = [0x5a827999, 0x6ed9eba1, 0x8f1bbcdc, 0xca62c1d6];

    // PREPROCESSING 
 
    msg += String.fromCharCode(0x80); // add trailing '1' bit to string [5.1.1]

    // convert string msg into 512-bit/16-integer blocks arrays of ints [5.2.1]
    var l = Math.ceil(msg.length/4) + 2;  // long enough to contain msg plus 2-word length
    var N = Math.ceil(l/16);              // in N 16-int blocks
    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));
        }
    }
    // add length (in bits) into final pair of 32-bit integers (big-endian) [5.1.1]
    M[N-1][14] = ((msg.length-1) >>> 30) * 8;
    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); var a, b, c, d, e;
    for (var i=0; i<N; i++) {

        // 1 - prepare message schedule 'W'
        for (var t=0;  t<16; t++) W[t] = M[i][t];
        for (var 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 (var 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
        H0 = (H0+a) & 0xffffffff;  // note 'addition modulo 2^32'
        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);

    // =========================================================================
    // private function: 'f' [4.1.1]
    // =========================================================================
    function f(s, x, y, z) 
    {
        switch (s) {
        case 0: return (x & y) ^ (~x & z);
        case 1: return x ^ y ^ z;
        case 2: return (x & y) ^ (x & z) ^ (y & z);
        case 3: return x ^ y ^ z;
        }
    }

    // =========================================================================
    // private function: rotate left (circular left shift) value x by n
    // positions [3.2.5]
    // =========================================================================
    function ROTL(x, n)
    {
        return (x<<n) | (x>>>(32-n));
    }

    // =========================================================================
    // private function: tailored hex->string method (note toString(16) is
    // implementation-dependant, and in IE returns signed numbers when used
    // on full words)
    // =========================================================================
    function toHexStr(value)
    {
        var s="", v;
        for (var i=7; i>=0; i--) { v = (value>>>(i*4)) & 0xf; s += v.toString(16); }
        return s;
    }
}