/*
 *
 * A JavaScript implementation of the Secure Hash Algorithm, SHA-1, as defined
 * in FIPS PUB 180-1
 *
 * By lizq
 *
 * 2006-11-11
 *
 */
/*
 *
 * Configurable variables.
 *
 */
var hexcase = 0; /* hex output format. 0 - lowercase; 1 - uppercase */
var chrsz = 8; /* bits per input character. 8 - ASCII; 16 - Unicode */
/*
 *
 * The main function to calculate message digest
 *
 */
function hex_sha1(s){
    return binb2hex(core_sha1(AlignSHA1(s)));
}
/*
 *
 * Perform a simple self-test to see if the VM is working
 *
 */
function sha1_vm_test(){
    return hex_sha1("abc") == "a9993e364706816aba3e25717850c26c9cd0d89d";
}
/*
 *
 * Calculate the SHA-1 of an array of big-endian words, and a bit length
 *
 */
function core_sha1(blockArray){
    var x = blockArray; // append padding
    var w = Array(80);
    var a = 1732584193;
    var b = -271733879;
    var c = -1732584194;
    var d = 271733878;
    var e = -1009589776;
    for (var i = 0; i < x.length; i += 16) // 每次處理512位 16*32
    {
        var olda = a;
        var oldb = b;
        var oldc = c;
        var oldd = d;
        var olde = e;
        for (var j = 0; j < 80; j++) // 對每個512位進行80步操作
        {
            if (j < 16) 
                w[j] = x[i + j];
            else
                w[j] = rol(w[j - 3] ^ w[j - 8] ^ w[j - 14] ^ w[j - 16], 1);
            var t = safe_add(safe_add(rol(a, 5), sha1_ft(j, b, c, d)), safe_add(safe_add(e, w[j]), sha1_kt(j)));
            e = d;
            d = c;
            c = rol(b, 30);
            b = a;
            a = t;
        }
        a = safe_add(a, olda);
        b = safe_add(b, oldb);
        c = safe_add(c, oldc);
        d = safe_add(d, oldd);
        e = safe_add(e, olde);
    }
    return new Array(a, b, c, d, e);
}
/*
 *
 * Perform the appropriate triplet combination function for the current
 * iteration
 *
 * 返回對應F函數的值
 *
 */
function sha1_ft(t, b, c, d){
    if (t < 20) 
        return (b & c) | ((~ b) & d);
    if (t < 40) 
        return b ^ c ^ d;
    if (t < 60) 
        return (b & c) | (b & d) | (c & d);
    return b ^ c ^ d; // t<80
}
/*
 *
 * Determine the appropriate additive constant for the current iteration
 *
 * 返回對應的Kt值
 *
 */
function sha1_kt(t){
    return (t < 20) ? 1518500249 : (t < 40) ? 1859775393 : (t < 60) ? -1894007588 : -899497514;
}
/*
 *
 * Add integers, wrapping at 2^32. This uses 16-bit operations internally
 *
 * to work around bugs in some JS interpreters.
 *
 * 將32位數拆成高16位和低16位分別進行相加，從而實現 MOD 2^32 的加法
 *
 */
function safe_add(x, y){
    var lsw = (x & 0xFFFF) + (y & 0xFFFF);
    var msw = (x >> 16) + (y >> 16) + (lsw >> 16);
    return (msw << 16) | (lsw & 0xFFFF);
}
/*
 *
 * Bitwise rotate a 32-bit number to the left.
 *
 * 32位二進制數循環左移
 *
 */
function rol(num, cnt){
    return (num << cnt) | (num >>> (32 - cnt));
}
/*
 *
 * The standard SHA1 needs the input string to fit into a block
 *
 * This function align the input string to meet the requirement
 *
 */
function AlignSHA1(str){
    var nblk = ((str.length + 8) >> 6) + 1, blks = new Array(nblk * 16);
    for (var i = 0; i < nblk * 16; i++) 
        blks[i] = 0;
    for (i = 0; i < str.length; i++) 
        blks[i >> 2] |= str.charCodeAt(i) << (24 - (i & 3) * 8);
    blks[i >> 2] |= 0x80 << (24 - (i & 3) * 8);
    blks[nblk * 16 - 1] = str.length * 8;
    return blks;
}
/*
 *
 * Convert an array of big-endian words to a hex string.
 *
 */
function binb2hex(binarray){
    var hex_tab = hexcase ? "0123456789ABCDEF" : "0123456789abcdef";
    var str = "";
    for (var i = 0; i < binarray.length * 4; i++) {
        str += hex_tab.charAt((binarray[i >> 2] >> ((3 - i % 4) * 8 + 4)) & 0xF) +
        hex_tab.charAt((binarray[i >> 2] >> ((3 - i % 4) * 8)) & 0xF);
    }
    return str;
}
/*
 *
 * calculate MessageDigest accord to source message that inputted
 *
 */
function calcDigest(){
    var digestM = hex_sha1(document.SHAForm.SourceMessage.value);
    document.SHAForm.MessageDigest.value = digestM;
}