version 0.51


   my $xml = '<foo ID="abc">123</foo>';
   my $signer = XML::Sig->new({
     key => 'path/to/private.key',

   # create a signature
   my $signed = $signer->sign($xml);
   print "Signed XML: $signed\n";

   # verify a signature
     or die "Signature Invalid.";
   print "Signature valid.\n";


This perl module provides two primary capabilities: given an XML string, create and insert digital signatures, or if one is already present in the string verify it -- all in accordance with the W3C standard governing XML signatures.


XML::Sig - A toolkit to help sign and verify XML Digital Signatures.




This module supports the following signature methods:

  • DSA

  • RSA

  • RSA encoded as x509


  • ECDSA encoded as x509

  • HMAC

This module supports the following canonicalization methods and transforms:

  • Enveloped Signature

  • REC-xml-c14n-20010315#

  • REC-xml-c14n-20010315#WithComments

  • REC-xml-c14n11-20080502

  • REC-xml-c14n11-20080502#WithComments

  • xml-exc-c14n#

  • xml-exc-c14n#WithComments


Each of the following options are also accessors on the main XML::Sig object. TODO Not strictly correct rewrite


The path to a file containing the contents of a private key. This option is used only when generating signatures.


The path to a file containing a PEM-formatted X509 certificate. This option is used only when generating signatures with the "x509" option. This certificate will be embedded in the signed document, and should match the private key used for the signature.


A string containing a PEM-formatted X509 certificate. This option is used only when generating signatures with the "x509" option. This certificate will be embedded in the signed document, and should match the private key used for the signature.


Takes a true (1) or false (0) value and indicates how you want the signature to be encoded. When true, the X509 certificate supplied will be encoded in the signature. Otherwise the native encoding format for RSA, DSA and ECDSA will be used.


Passing sig_hash to new allows you to specify the SignatureMethod hashing algorithm used when signing the SignedInfo. RSA and ECDSA supports the hashes specified sha1, sha224, sha256, sha384 and sha512

DSA supports only sha1 and sha256 (but you really should not sign anything with DSA anyway).


Passing digest_hash to new allows you to specify the DigestMethod hashing algorithm used when calculating the hash of the XML being signed. Supported hashes can be specified sha1, sha224, sha256, sha384, sha512, ripemd160


Base64 encoded hmac_key


Some applications such as Net::SAML2 expect to sign a fragment of the full XML document so is this is true (1) it will not include the XML Declaration at the beginning of the signed XML. False (0) or undefined returns an XML document starting with the XML Declaration.



Constructor; see OPTIONS above.


When given a string of XML, it will return the same string with a signature generated from the key provided when the XML::Sig object was initialized.

This method will sign all elements in your XML with an ID (case sensitive) attribute. Each element with an ID attribute will be the basis for a seperate signature. It will correspond to the URI attribute in the Reference element that will be contained by the signature. If no ID attribute can be found on an element, the signature will not be created.

The elements are signed in reverse order currently assuming (possibly incorrectly) that the lower element in the tree may need to be signed inclusive of its Signature because it is a child of the higher element.

Arguments: $xml: string XML string

Returns: string Signed XML


Returns true or false based upon whether the signature is valid or not.

When using XML::Sig exclusively to verify a signature, no key needs to be specified during initialization given that the public key should be transmitted with the signature.

XML::Sig checks all signature in the provided xml and will fail should any signature pointing to an existing ID in the XML fail to verify.

Should there be a Signature included that does not point to an existing node in the XML it is ignored and other Signaures are checked. If there are no other Signatures it will return false.

Arguments: $xml: string XML string

Returns: string Signed XML


Following a successful verify with an X509 certificate, returns the signer's certificate as embedded in the XML document for verification against a CA certificate. The certificate is returned as a Crypt::OpenSSL::X509 object.

Arguments: none

Returns: Crypt::OpenSSL::X509: Certificate used to sign the XML


Just as one might want to send an email message that is cryptographically signed in order to give the recipient the means to independently verify who sent the email, one might also want to sign an XML document. This is especially true in the scenario where an XML document is received in an otherwise unauthenticated context, e.g. SAML.

However XML provides a challenge that email does not. In XML, two documents can be byte-wise inequivalent, and semanticaly equivalent at the same time. For example:

    <?xml version="1.0"?>
      <bar />


    <?xml version="1.0"?>

Each of these document express the same thing, or in other words they "mean" the same thing. However if you were to strictly sign the raw text of these documents, they would each produce different signatures.

XML Signatures on the other hand will produce the same signature for each of the documents above. Therefore an XML document can be written and rewritten by different parties and still be able to have someone at the end of the line verify a signature the document may contain.

There is a specially subscribed methodology for how this process should be executed and involves transforming the XML into its canonical form so a signature can be reliably inserted or extracted for verification. This module implements that process.


Below is a sample XML signature to give you some sense of what they look like. First let's look at the original XML document, prior to being signed:

  <?xml version="1.0"?>
  <foo ID="abc">

Now, let's insert a signature:

  <?xml version="1.0"?>
  <foo ID="abc">
    <Signature xmlns="">
      <SignedInfo xmlns="" xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" xmlns:xenc="">
        <CanonicalizationMethod Algorithm="" />
        <SignatureMethod Algorithm="" />
        <Reference URI="#abc">
            <Transform Algorithm="" />
          <DigestMethod Algorithm="" />




Author: Byrne Reese <>

Thanks to Manni Heumann who wrote Google::SAML::Response from which this module borrows heavily in order to create digital signatures.

Net::SAML2 embedded version amended by Chris Andrews <>.

Maintainer: Timothy Legge <>


  • Byrne Reese <>

  • Timothy Legge <>


This software is copyright (c) 2021 by Byrne Reese, Chris Andrews and Others; in detail:

  Copyright 2009       Byrne, Michael Hendricks
            2010       Chris Andrews
            2011       Chris Andrews, Oskari Okko Ojala
            2012       Chris Andrews, Peter Marschall
            2015       Mike Wisener
            2016       Jeff Fearn
            2017       Mike Wisener, xmikew
            2019-2021  Timothy Legge

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.