How to produce XML signature with no whitespaces and line-breaks in Java?

Question

I work with the brazilian "Nota Fiscal Eletronica" project, in which they define a standart way to sign XML documents.

Recently, they started to require that there are absolutely no whitespaces between tags, including signature tags (*).

We happen to use apache's XMLSignature and I can't seem to produce an unindented signature.

If I remove the whitespaces after signing, the signature gets broken.

I cannot change the canonicalizer / transformers set either, since they're predefined.

I couldn't find an option or parameter in the XMLSignature API to control indentation or whitespaces.

Below is the code:

    // the element where to insert the signature
    Element element = ...;
    X509Certificate cert = ...;
    PrivateKey privateKey = ...;

    XMLSignature signer =
            new XMLSignature(doc, "http://xml-security",
            XMLSignature.ALGO_ID_SIGNATURE_RSA_SHA1);

    element.appendChild(signer.getElement());

    Transforms transforms = new Transforms(doc);

    // Define as regras de transformação e canonicalização do documento
    // XML, necessário para fazer a verificação do parsing e da
    // assinatura pelos destinatários
    transforms.addTransform(Transforms.TRANSFORM_ENVELOPED_SIGNATURE); //, xpath.getElementPlusReturns());

    transforms.addTransform(Transforms.TRANSFORM_C14N_OMIT_COMMENTS); //,xpath.getElementPlusReturns());

    String id = "";

    id = ((Element) element.getElementsByTagName("infNFe").item(0)).getAttributeNode("Id").getNodeValue();

    signer.addDocument("#" + id, transforms, 
                       Constants.ALGO_ID_DIGEST_SHA1);
    signer.addKeyInfo(cert);
    signer.sign(privateKey);

And below is the resulting signature (snippet):

<Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
<SignedInfo>
<CanonicalizationMethod Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315"/>
<SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"/>
<Reference URI="#NFe43110189716583000165550010000076011492273645">
<Transforms>
<Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/>
<Transform Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315"/>
</Transforms>
<DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
<DigestValue>fas0ra5uRskQgRHSrIYhEjFEjKQ=</DigestValue>
</Reference>
</SignedInfo>
<SignatureValue>
2RGltUZy0HfNoiKtVanAeN+JUPyglWDuQNnMudSgA7kESoHBZ/q/GMbc+xMSN1eV8u7+2PxSKl1T
Zl592FWmCSAkL8pwMujDxJ4iTLU20Hf0dNF7oGcyB+g9GgbipW2udq0kwJLz6HzXUD/Evf/0y+3T
NtsXeIaA6A29ttD/UEs=
</SignatureValue>
<KeyInfo>
<X509Data>
<X509Certificate>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</X509Certificate>
</X509Data>
</KeyInfo>
</Signature>

Notice the (unwanted) line-breaks.

Any help would be greatly appreciated.

Thanks a lot in advance.

(*) Clarification: the new rule forbids whitespaces (or any other text) between element-only tags. As an example, this would be allowed:

<a><b>
  text
  inside
  tag
</b></a>

while this would be forbidden:

<a>
<b>text</b>
</a>

because on the latter case, the whitespaces (line-breaks) are between two tags, or, in other words, placed inside an element-only tag.

Answer 1

You can simply set -Dorg.apache.xml.security.ignoreLineBreaks=true for disabling '\n' in XML generation. original mail

bug description

Answer 2

the signature blocks are encoding binary information as Base64, which must follow some formating including line breaks (see http://en.wikipedia.org/wiki/Base64). So you simply can't remove them without alter the information.

a better way to redure network traffic, is to use comression before sending data.

Answer 3

Fortunately XMLSignature is opensource, so I guess you'll have to get the source code and hack it your self.

Probably your solution will help others in the future so, create a patch and send it back to the project.

Good luck!

:) :)

Answer 4

I found a (shameful) solution.

It's not the expected solution, though: replacing apache's API with javax.xml.crypto API.

Here's the changed code:

// the element where to insert the signature
Element element = ...;
X509Certificate cert = ...;
PrivateKey privateKey = ...;
// Create a DOM XMLSignatureFactory that will be used to
// generate the enveloped signature.
XMLSignatureFactory fac = XMLSignatureFactory.getInstance("DOM");

// Create a Reference to the enveloped document (in this case,
// you are signing the whole document, so a URI of "" signifies
// that, and also specify the SHA1 digest algorithm and
// the ENVELOPED Transform.
List<Transform> transformList = new ArrayList<Transform>();
TransformParameterSpec tps = null;
Transform envelopedTransform;
try {
    envelopedTransform = fac.newTransform(Transform.ENVELOPED,
            tps);
    Transform c14NTransform = fac.newTransform(
            "http://www.w3.org/TR/2001/REC-xml-c14n-20010315", tps);

    transformList.add(envelopedTransform);
    transformList.add(c14NTransform);
} catch (NoSuchAlgorithmException e) {
    throw new RuntimeException("Erro inesperado: " + e.getMessage(), e);
} catch (InvalidAlgorithmParameterException e) {
    throw new RuntimeException("Erro inesperado: " + e.getMessage(), e);
}

// Create the KeyInfo containing the X509Data.
KeyInfoFactory kif = fac.getKeyInfoFactory();
List<Serializable> x509Content = new ArrayList<Serializable>();
x509Content.add(cert);
javax.xml.crypto.dsig.keyinfo.X509Data xd = kif.newX509Data(x509Content);
KeyInfo ki = kif.newKeyInfo(Collections.singletonList(xd));

// Obtem elemento do documento a ser assinado, será criado uma
// REFERENCE para o mesmo
Element el = (Element) element.getElementsByTagName(subTag).item(0);
String id = el.getAttribute("Id");

// Create a DOM XMLSignatureFactory that will be used to
// generate the enveloped signature.

Reference ref;
javax.xml.crypto.dsig.SignedInfo si;
try {
    ref = fac.newReference("#" + id, fac.newDigestMethod(
            DigestMethod.SHA1, null), transformList, null, null);

    // Create the SignedInfo.
    si = fac.newSignedInfo(fac.newCanonicalizationMethod(
            CanonicalizationMethod.INCLUSIVE,
            (C14NMethodParameterSpec) null), fac.newSignatureMethod(SignatureMethod.RSA_SHA1, null),
            Collections.singletonList(ref));
} catch (NoSuchAlgorithmException e) {
    throw new RuntimeException("Erro inesperado: " + e.getMessage(), e);
} catch (InvalidAlgorithmParameterException e) {
    throw new RuntimeException("Erro inesperado: " + e.getMessage(), e);
}

// Create the XMLSignature, but don't sign it yet.
javax.xml.crypto.dsig.XMLSignature signature = fac.newXMLSignature(si, ki);

// Marshal, generate, and sign the enveloped signature.
// Create a DOMSignContext and specify the RSA PrivateKey and
// location of the resulting XMLSignature's parent element.
DOMSignContext dsc = new DOMSignContext(privateKey, element);
signature.sign(dsc);

This API produces the signature with no whitespaces between tags at all.

Still would like to see a solution for apache's API, since this code was very mature already, and we wouldn't like to risk as much as changing the entire signature implementation.

Answer 5

We just need to set the "true" value to the "ignoreLineBreaks" parameter, cause' the default value is false and this allows to the signature API to add LineBreaks

here is the code to avoid or remove LineBreaks

Field f = XMLUtils.class.getDeclaredField("ignoreLineBreaks");
f.setAccessible(true);
f.set(null, Boolean.TRUE);

then, we'll can make sure that the new value is true with the next code line

System.err.println(XMLUtils.ignoreLineBreaks());

I had the same problem and this worked for me.

Answer 6

You can try:

System.setProperty("org.apache.xml.security.ignoreLineBreaks", "true");

Answer 7

XML Signature signs part of an XML Document starting with a given element (i.e. a sub tree in DOM) after it is normalized with a C14N algorithm. The standard C14N algorithm you use preserves line breaks and white spaces (see http://www.w3.org/TR/xml-c14n#Example-WhitespaceInContent).

So all line breaks in the signed part of the original document (including between last tag of data and the <Signature> tag, and between </Signature> and the next closing tag) *must be preserved so as not to alter the signature. The line breaks and spaces in the Signature element itself are not important and may be removed without altering the signature.

Here an example:

<root id="signedpart">
  <data>
     ...
  </data>
  <Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
     <SignedInfo>
       <Reference URI="#signedpart">
          ...
       </Reference>
     </SignedInfo>
  </Signature>
</root> 

Here are your possible options:

1. define your own C14N algorithm that will remove spaces and line breaks by it self. I would discourage this as the other side must also use this non standard C14N algorithm.

2. remove line breaks an spaces from you XML before signing it (and potentially remove spaces in signature afterwards)

with the example this will give you the following signed XML:

<root id="signedpart"><data>...</data><Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
    <SignedInfo>
       <Reference URI="#signedpart">
          ...
       </Reference>
     </SignedInfo>
  </Signature></root>

and after removing spaces in signature

<root id="signedpart"><data>...</data><Signature xmlns="http://www.w3.org/2000/09/xmldsig#"><SignedInfo><Reference URI="#signedpart">...</Reference></SignedInfo></Signature></root>