Thursday, September 22, 2016

Using SHA-512 with Apache CXF SOAP web services

XML Signature is used extensively in SOAP web services to guarantee message integrity, non-repudiation, as well as client authentication via PKI. A digest algorithm crops up in XML Signature both as part of the Signature Method (rsa-sha1 for example), as well as in the digests of the data that are signed. As recent weaknesses have emerged with the use of SHA-1, it makes sense to use the SHA-2 digest algorithm instead. In this post we will look how to configure Apache CXF to use SHA-512 (i.e. SHA-2 with 512 bits) as the digest algorithm.

1) Configuring the STS to use SHA-512

Apache CXF ships with a SecurityTokenService (STS) that is widely deployed. The principal function of the STS is to issue signed SAML tokens, although it supports a wide range of other functionalities and token types. The STS (for more recent versions of CXF) uses RSA-SHA256 for the signature method when signing SAML tokens, and uses SHA-256 for the digest algorithm. In this section we'll look at how to configure the STS to use SHA-512 instead.

You can specify signature and digest algorithms via the SignatureProperties class in the STS. To specify SHA-512 for signature and digest algorithms for generated tokens in the STS add the following bean to your spring configuration:

Next you need to reference this bean in the StaticSTSProperties bean for your STS:
  • <property name="signatureProperties" ref="sigProps" />
2) Configuring WS-SecurityPolicy to use SHA-512

Service requests are typically secured at a message level using WS-SecurityPolicy. It is possibly to specify the algorithms used to secure the request, as well as the key sizes, by configuring an AlgorithmSuite policy. Unfortunately the last WS-SecurityPolicy spec is quite dated at this point, and lacks support for more modern algorithms as part of the default AlgorithmSuite policies that are defined in the spec. The spec only supports using RSA-SHA1 for signature, and only SHA-1 and SHA-256 for digest algorithms.

Luckily, Apache CXF users can avail of a few different ways to use stronger algorithms with web service requests. In CXF there is a JAX-WS property called 'ws-security.asymmetric.signature.algorithm' for AsymmetricBinding policies (similarly 'ws-security.symmetric.signature.algorithm' for SymmetricBinding policies). This overrides the default signature algorithm of the policy. So for example, to switch to use RSA-SHA512 instead of RSA-SHA1 simply set the following property on your client/endpoint:
  • <entry key="ws-security.asymmetric.signature.algorithm" value=""/>
There is no corresponding property to explicitly configure the digest algorithm, as the default AlgorithmSuite policies already support SHA-256 (although one could be added if there was enough demand). If you really need to support SHA-512 here, an option is to use a custom AlgorithmSuite (which will obviously not be portable), or to override one of the existing ones.

It's pretty straightforward to do this. First you need to create an AlgorithmSuiteLoader implementation to handle the policy. Here is one used in the tests that creates a custom AlgorithmSuite policy called 'Basic128RsaSha512', which extends the 'Basic128' policy to use RSA-SHA512 for the signature method, and SHA-512 for the digest method. This AlgorithmSuiteLoader can be referenced in Spring via:

The policy in question looks like:
  • <cxf:Basic128RsaSha512 xmlns:cxf=""/>

No comments:

Post a Comment