bitaddress.org/src/ninja.splitwallet.js

ninja.wallets.splitwallet = {
    open: function () {
        document.getElementById("splitarea").style.display = "block";
        secrets.setRNG();
        secrets.init(7);
    },

    close: function () {
        document.getElementById("splitarea").style.display = "none";
    },

    mkOutputRow: function(s,id,lbltxt) {
        var row = document.createElement("span");
        var label = document.createElement("label");
        label.innerHTML= lbltxt + s;
        var qr = document.createElement("div");

        qr.setAttribute("id", id);
        row.appendChild(label);
        row.appendChild(qr);
        row.appendChild(document.createElement("br"));

        return row;

    },

    stripLeadZeros: function(hex) { return hex.split(/^0+/).slice(-1)[0]; },

    hexToBytes: function (hex) {
        //if input has odd number of digits, pad it
        if (hex.length % 2 == 1)
            hex = "0" + hex;
  	for (var bytes = [], c = 0; c < hex.length; c += 2)
 	    bytes.push(parseInt(hex.substr(c, 2), 16));
 	return bytes;
    },

    // Split a private key and update information in the HTML
    splitKey: function () {
        try {
            var key = new Bitcoin.ECKey(false);
            var bitcoinAddress = key.getBitcoinAddress();
            var element = document.getElementById("splitoutput");
            if (element != null) element.parentNode.removeChild(element);

            var numshares = parseInt(document.getElementById('splitshares').value);
            var threshhold =  parseInt(document.getElementById('splitthreshhold').value);
            var shares = secrets.share(Crypto.util.bytesToHex(key.getBitcoinPrivateKeyByteArray()),
                                       numshares, threshhold).map(this.hexToBytes).map(Bitcoin.Base58.encode);
            var output = document.createElement("div");
            output.setAttribute("id", "splitoutput");
            var m = {};
            output.appendChild(this.mkOutputRow(bitcoinAddress, "split_addr", "Bitcoin Address:    "));
            m["split_addr"] = bitcoinAddress;

            for (var i=0; i < shares.length; i++) {
                var id = "split_qr_"+ i;
                output.appendChild(this.mkOutputRow(shares[i], id, "Share " + (i+1) + ":          "));
                m[id]=shares[i];
            }

            document.getElementById("splitcommands").appendChild(output);
            ninja.qrCode.showQrCode(m);

        }
        catch (e) {
            // browser does not have sufficient JavaScript support to generate a bitcoin address
            alert(e);
            document.getElementById("btcaddress").innerHTML = "error";
            document.getElementById("btcprivwif").innerHTML = "error";
            document.getElementById("qrcode_public").innerHTML = "";
            document.getElementById("qrcode_private").innerHTML = "";
        }
    },

    // Combine shares of a private key to retrieve the key
    combineShares: function () {
        try {
            var element = document.getElementById("combineoutput");
            if (element != null) element.parentNode.removeChild(element);

            var shares = document.getElementById("combineinput").value.trim().split(/\W+/);

            var combined = secrets.combine(shares.map(Bitcoin.Base58.decode).
                                           map(Crypto.util.bytesToHex).
                                           map(this.stripLeadZeros));

            var privkeyBase58 = new Bitcoin.ECKey(this.hexToBytes(combined)).getBitcoinWalletImportFormat();
            var output = document.createElement("div");
            output.setAttribute("id", "combineoutput");
            var txt = document.createElement("input");
            txt.setAttribute("id","combineoutputtext");
            txt.setAttribute("value",privkeyBase58);
            txt.setAttribute("size",55);
            var lbl = document.createElement("label");
            lbl.innerHTML="Private key";
            output.appendChild(lbl);
            output.appendChild(txt);
            document.getElementById("combinecommands").appendChild(output);
        }
        catch (e) {
            alert(e);
        }

    }
};