Friday, January 13, 2012

Apache Santuario (XML Security for Java) 1.5.0 RC2

I posted a RC1 for Apache Santuario (XML Security for Java) almost a month ago now. Since then, a large number of changes have been made to address some inconsistencies in RC1 as well to add some new functionality. The RC2 release is available here. Please download it and post any issues that are found to the mailing list. The changes compared to the RC1 release (documented here) are as follows:

1) Support for RSA-OAEP key transport algorithms with strong digests

The 1.4.x releases only support using SHA-1 with the RSA-OAEP key transport algorithm for encryption and decryption. The 1.5.0 RC2 release supports stronger digests using the ds:DigestMethod child of xenc:EncrytionMethod. In addition, it fully supports the xenc11:MGF Algorithm as documented in the XML Encryption 1.1 specification.

To test this functionality, all of the XML Encryption 1.1 Key Wrapping test-cases have been implemented, both for encryption and decryption. These tests also serve to better test the support for GCM algorithms in the 1.5.0 release. Support for 192 bit AES-GCM was added as part of this work. 

2) Major changes to how Elements are resolved

The release notes for RC1 described how the IdResolver no longer searches the current Document for an Element matching the requested Id in certain "known" namespaces, and instead how it was the responsibility of the user to register Elements by Id in the IdResolver (or via setIdAttributeNS if using the JSR-105 API), if they are required as part of the signature validation process.

In RC2, the static cache of Id->Elements that was maintained in the IdResolver has been removed. Instead, the ResourceResolver implementations that are responsible for resolving same-Document URI references resolve Elements by querying Document.getElementById(). The IdResolver has been deprecated, so that it is no longer possible to register an Element by Id, and the "get" methods simply delegate to the DOM call above.

So what does this mean for the user? The user is now responsible for registering any same-Document Elements by Id, which must be resolved as part of the signature creation/validation process. This can be done in two ways:
  1. Using the DOM APIs: Element.setIdAttribute*
  2. Using the JSR-105 API: DOMCryptoContext.setIdAttributeNS
3) Better protection against Signature Wrapping Attacks

A Signature Wrapping attack can occur when a malicious entity duplicates some signed Element in a document, and then modifies the content of the duplicated Element, but keeps the same Id. If the signature validation process only finds the initial Element, then signature validation will pass, and the user might be fooled into thinking that the modified Element has been signed, as it has the same Id as the original validated Element.

The implication of this attack is that it is vital that the user checks that the Elements that were signed correspond to the Elements that he/she expects to be signed. In other words, the Elements that were signed should be located in a specific "known" place in the Document. The best way of facilitating this check is to make sure that the signature validation process returns the Elements that it validated. The JSR-105 API supports this via the "javax.xml.crypto.dsig.cacheReference" boolean property, that can be set on the context.

However, the older XMLSignature, which pre-dates the JSR-105 API, did not include this functionality. This has been fixed in the RC2 release, e.g.:

XMLSignature signature = ...
// Perform validation and then...
SignedInfo signedInfo = signature.getSignedInfo();
for (int i = 0; i < signedInfo.getLength(); i++) {
    Reference reference = signedInfo.item(i);
    ReferenceData refData = reference.getReferenceData();

ReferenceData is a new interface that duplicates the way the JSR-105 API returns references. Three different implementations have been provided depending on whether the dereferenced Element is a NodeSet, Element or OctetStream.

Finally, some new functionality has been added when secure validation is enabled, to ensure that when an Element is de-referenced via Document.getElementById() (as described above), no other Element in the tree has an Attribute that is also registered as an Id with the same value. This is done via a tree search, and guarantees that the Element retrieved via the getElementById call is unique in the Document (something that is not guaranteed by the contract of getElementById). However note that another Element could still exist in the tree with a matching Id in another namespace.

1 comment:

  1. I just moved to 1.5.x and now I'm facing the following problem:

    Cannot resolve element with ID xxx

    I think it is related to point 2) Major changes to how Elements are resolved but how can I make use of "Using the DOM APIs: Element.setIdAttribute*"