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

You can try:

static {
    System.setProperty("com.sun.org.apache.xml.internal.security.ignoreLineBreaks", "true");
    com.sun.org.apache.xml.internal.security.Init.init();
}

Or

static {
    System.setProperty("org.apache.xml.security.ignoreLineBreaks", "true");
    org.apache.xml.security.Init.init();
}

Add this to the class which does signature job.

Answer 4

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!

:) :)