source: aportesmurachi/tahel/Murachi-pre/sign.js

function signText(text) {
    if (window.event) {
        window.event.cancelBubble = true;
        }
    return sign(text);
}

function sign(src) {
    if (window.crypto && window.crypto.signText) {
        return sign_NS(src);
        }
        if (isIE()) {
                return sign_IE(src);
        }
        
        alert("Sorry, your browser is not supported");
        return "";
}

function sign_NS(src) {
    return crypto.signText(src, "ask");
}

// CAPICOM constants
var CAPICOM_STORE_OPEN_READ_ONLY = 0;
var CAPICOM_CURRENT_USER_STORE = 2;
var CAPICOM_CERTIFICATE_FIND_SHA1_HASH = 0;
var CAPICOM_CERTIFICATE_FIND_EXTENDED_PROPERTY = 6;
var CAPICOM_CERTIFICATE_FIND_TIME_VALID = 9;
var CAPICOM_CERTIFICATE_FIND_KEY_USAGE = 12;
var CAPICOM_DIGITAL_SIGNATURE_KEY_USAGE = 0x00000080;
var CAPICOM_AUTHENTICATED_ATTRIBUTE_SIGNING_TIME = 0;
var CAPICOM_INFO_SUBJECT_SIMPLE_NAME = 0;
var CAPICOM_ENCODE_BASE64 = 0;
var CAPICOM_E_CANCELLED = -2138568446;
var CERT_KEY_SPEC_PROP_ID = 6;

function isIE() {
        if ("ActiveXObject" in window){
                return true;
        }
        return false;
}

function findCertificateByHash() {
    try {
        // instantiate the CAPICOM objects
        var store = new ActiveXObject("CAPICOM.Store");
        // open the current users personal certificate store
        store.Open(CAPICOM_CURRENT_USER_STORE, "My", CAPICOM_STORE_OPEN_READ_ONLY);

        var certificates = store.Certificates.Select(); 
                                        
        var signer = new ActiveXObject("CAPICOM.Signer");
        signer.Certificate = certificates.Item(1);
        return signer;
    } catch (e) {
        if (e.number != CAPICOM_E_CANCELLED) {
            return new ActiveXObject("CAPICOM.Signer");
        }
    }
}

function sign_IE(src) {
    try {
        // instantiate the CAPICOM objects
        var signedData = new ActiveXObject("CAPICOM.SignedData");
        var timeAttribute = new ActiveXObject("CAPICOM.Attribute");

        // Set the data that we want to sign
        signedData.Content = src;
        var signer = findCertificateByHash();

        // Set the time in which we are applying the signature
        var today = new Date();
        timeAttribute.Name = CAPICOM_AUTHENTICATED_ATTRIBUTE_SIGNING_TIME;
        timeAttribute.Value = today.getVarDate();
        signer.AuthenticatedAttributes.Add(timeAttribute);

        // Do the Sign operation
        var signed = signedData.Sign(signer, true, CAPICOM_ENCODE_BASE64);
                // Important: IE uses UTF-16LE to encode the signed data
        return signed;
    } catch (e) {
        if (e.number != CAPICOM_E_CANCELLED) {
            alert("An error occurred when attempting to sign the content, the error was: " + e.description);
        }
    }
    return "";
}