Xml digital signature and encryption library for Node.js

An xml digital signature library for node. Xml encryption is coming soon. Written in pure javascript!

For more information visit my blog or my twitter.

Install with npm:

npm install xml-crypto

A pre requisite it to have openssl installed and its /bin to be on the system path. I used version 1.0.1c but it should work on older versions too.

by default the following algorithms are used:

Canonicalization/Transformation Algorithm: Exclusive Canonicalization http://www.w3.org/2001/10/xml-exc-c14n#

Hashing Algorithm: SHA1 digest http://www.w3.org/2000/09/xmldsig#sha1

Signature Algorithm: RSA-SHA1 http://www.w3.org/2000/09/xmldsig#rsa-sha1

You are able to extend xml-crypto with custom algorithms.

When signing a xml document you can specify the following properties on a SignedXml instance to customize the signature process:

  • sign.signingKey - [required] a Buffer or pem encoded String containing your private key
  • sign.keyInfoProvider - [optional] a key info provider instance, see customizing algorithms for an implementation example
  • sign.signatureAlgorithm - [optional] one of the supported signature algorithms. Ex: sign.signatureAlgorithm = "http://www.w3.org/2001/04/xmldsig-more#rsa-sha256"
  • sign.canonicalizationAlgorithm - [optional] one of the supported canonicalization algorithms. Ex: sign.canonicalizationAlgorithm = "http://www.w3.org/2001/10/xml-exc-c14n#WithComments"

Use this code:

var SignedXml = require('xml-crypto').SignedXml   
  , fs = require('fs')
var xml = "<library>" +
            "<book>" +
              "<name>Harry Potter</name>" +
            "</book>" +
var sig = new SignedXml()
sig.signingKey = fs.readFileSync("client.pem")
fs.writeFileSync("signed.xml", sig.getSignedXml())

The result will be:

  <book Id="_0">
    <name>Harry Potter</name>
  <Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
      <CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#" />
      <SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1" />
      <Reference URI="#_0">
          <Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#" />
        <DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" />
    <SignatureValue>vhWzpQyIYuncHUZV9W...[long base64 removed]...</SignatureValue>


To generate a <X509Data></X509Data> element in the signature you must provide a key info implementation, see customizing algorithms for an example.

When verifying a xml document you must specify the following properties on a ``SignedXml` instance:

  • sign.keyInfoProvider - [required] a key info provider instance containing your certificate, see customizing algorithms for an implementation example

You can use any dom parser you want in your code (or none, depending on your usage). This sample uses xmldom so you should install it first:

npm install xmldom


var select = require('xml-crypto').xpath
  , dom = require('xmldom').DOMParser
  , SignedXml = require('xml-crypto').SignedXml
  , FileKeyInfo = require('xml-crypto').FileKeyInfo  
  , fs = require('fs')
var xml = fs.readFileSync("signed.xml").toString()
var doc = new dom().parseFromString(xml)    
var signature = select(doc, "/*/*[local-name(.)='Signature' and namespace-uri(.)='http://www.w3.org/2000/09/xmldsig#']")[0]
var sig = new SignedXml()
sig.keyInfoProvider = new FileKeyInfo("client_public.pem")
var res = sig.checkSignature(xml)
if (!res) console.log(sig.validationErrors)

if the verification process fails sig.validationErrors will have the errors.


The xml-crypto api requires you to supply it separately the xml signature ("<Signature>...</Signature>", in loadSignature) and the signed xml (in checkSignature). The signed xml may or may not contain the signature in it, but you are still required to supply the signature separately.

See xpath.js for usage

The SignedXml constructor provides an abstraction for sign and verify xml documents. The object is constructed using new SignedXml([idMode]) where:

  • idMode - if the value of "wssecurity" is passed it will create/validate id's with the ws-security namespace.


A SignedXml object provides the following methods:

To sign xml documents:

  • addReference(xpath, [transforms], [digestAlgorithm]) - adds a reference to a xml element where:
    • xpath - a string containing a XPath expression referencing a xml element
    • transforms - an array of transform algorithms, the referenced element will be transformed for each value in the array
    • digestAlgorithm - one of the supported hashing algorithms
  • computeSignature(xml, [options]) - compute the signature of the given xml where:
    • xml - a string containing a xml document
    • options - an object with the following properties:
      • prefix - adds this value as a prefix for the generated signature tags
      • attrs - a hash of attributes and values attrName: value to add to the signature root node
      • location - customize the location of the signature, pass an object with a reference key which should contain a XPath expression to a reference node, an action key which should contain one of the following values: append, prepend, before, after
  • getSignedXml() - returns the original xml document with the signature in it, must be called only after computeSignature
  • getSignatureXml() - returns just the signature part, must be called only after computeSignature
  • getOriginalXmlWithIds() - returns the original xml with Id attributes added on relevant elements (required for validation), must be called only after computeSignature

To verify xml documents:

  • loadSignature(signatureXml) - loads the signature where:
    • signatureXml - a string or node object (like an xml-dom node) containing the xml representation of the signature
  • checkSignature(xml) - validates the given xml document and returns true if the validation was successful, sig.validationErrors will have the validation errors if any, where:
    • xml - a string containing a xml document

A basic key info provider implementation using fs.readFileSync(file), is constructed using new FileKeyInfo([file]) where:

  • file - a path to a pem encoded certificate

See verifying xml documents for an example usage

The following sample shows how to sign a message using custom algorithms.

First import some modules:

var SignedXml = require('xml-crypto').SignedXml
  , fs = require('fs')

Now define the extension point you want to implement. You can choose one or more.

A key info provider is used to extract and construct the key and the KeyInfo xml section. Implement it if you want to create a signature with a KeyInfo section, or you want to read your key in a different way then the default file read option.

function MyKeyInfo() {
  this.getKeyInfo = function(keyprefix) {
        prefix = prefix || ''
        prefix = prefix ? prefix + ':' : prefix
    return "<" + prefix + "X509Data></" + prefix + "X509Data>"
  this.getKey = function(keyInfo) {
    //you can use the keyInfo parameter to extract the key in any way you want       
    return fs.readFileSync("key.pem")

A custom hash algorithm is used to calculate digests. Implement it if you want a hash other than the default SHA1.

function MyDigest() {
  this.getHash = function(xml) {    
    return "the base64 hash representation of the given xml string"
  this.getAlgorithmName = function() {
    return "http://myDigestAlgorithm"

A custom signing algorithm. The default is RSA-SHA1

function MySignatureAlgorithm() {
  /*sign the given SignedInfo using the key. return base64 signature value*/
  this.getSignature = function(signedInfosigningKey) {            
    return "signature of signedInfo as base64..."
  this.getAlgorithmName = function() {
    return "http://mySigningAlgorithm"

Custom transformation algorithm. The default is exclusive canonicalization.

function MyTransformation() {
  /*given a node (from the xmldom module) return its canonical representation (as string)*/
  this.process = function(node) {   
   //you should apply your transformation before returning 
    return node.toString()
  this.getAlgorithmName = function() {
    return "http://myTransformation"

Custom canonicalization is actually the same as custom transformation. It is applied on the SignedInfo rather than on references.

function MyCanonicalization() {
  /*given a node (from the xmldom module) return its canonical representation (as string)*/
  this.process = function(node) {
    //you should apply your transformation before returning 
    return "< x/>"
   this.getAlgorithmName = function() {
    return "http://myCanonicalization"

Now you need to register the new algorithms:

/*register all the custom algorithms*/
SignedXml.CanonicalizationAlgorithms["http://MyTransformation"] = MyTransformation
SignedXml.CanonicalizationAlgorithms["http://MyCanonicalization"] = MyCanonicalization
SignedXml.HashAlgorithms["http://myDigestAlgorithm"] = MyDigest
SignedXml.SignatureAlgorithms["http://mySigningAlgorithm"] = MySignatureAlgorithm

Now do the signing. Note how we configure the signature to use the above algorithms:

function signXml(xmlxpathkeydest)
  var sig = new SignedXml()
  /*configure the signature object to use the custom algorithms*/
  sig.signatureAlgorithm = "http://mySignatureAlgorithm"
  sig.keyInfoProvider = new MyKeyInfo()
  sig.canonicalizationAlgorithm = "http://MyCanonicalization"
  sig.addReference("//*[local-name(.)='x']", ["http://MyTransformation"], "http://myDigestAlgorithm")
  sig.signingKey = fs.readFileSync(key)
  fs.writeFileSync(dest, sig.getSignedXml())
var xml = "<library>" +
            "<book>" +
              "<name>Harry Potter</name>" +

You can always look at the actual code as a sample (or drop me a mail).

Xml-Crypto internally relies on node's crypto module. This means pem encoded certificates are supported. So to sign an xml use key.pem that looks like this (only the begining of the key content is shown):


And for verification use key_public.pem:


Converting .pfx certificates to pem

If you have .pfx certificates you can convert them to .pem using openssl:

openssl pkcs12 -in c:\certs\yourcert.pfx -out c:\certs\cag.pem

Then you could use the result as is for the purpose of signing. For the purpose of validation open the resulting .pem with a text editor and copy from -----BEGIN CERTIFICATE----- to -----END CERTIFICATE----- (including) to a new text file and save it as .pem.

more examples coming soon

The test framework is nodeunit. To run tests use:

$> npm test

Visit my blog or my twitter