Add a section to the XML Signature tutorial that describes how to enable the secure mode of XML Signatures which allows you to block weak algorithms and other potentially insecure constructs.

New section: 

XML Signature Secure Validation Mode 

The secure validation mode for XML Signatures is a feature designed to protect you from XML Signatures that may contain potentially hostile constructs that can cause denial-of-service or other types of security issues. 

Secure validation mode is enabled by default when you run your application with a Security Manager. 

Secure validation mode can also be enabled by setting the org.jcp.xml.dsig.secureValidation property to TRUE. The property must be enabled before you validate the XML Signature. 

To set the property in an application, call the setProperty method of the javax.xml.crypto.dsig.dom.DOMValidateContext class: 

DOMValidateContext context = new DOMValidateContext(key, element); 
context.setProperty("org.jcp.xml.dsig.secureValidation", Boolean.TRUE); 

When secure validation mode is enabled, XML signatures are processed more securely. Limits are set on various XML signature constructs to avoid conditions such as denial-of-service attacks. By default, it enforces the following restrictions: 

    Forbids use of the XSLT Transform 
    Restricts the number of SignedInfo or Manifest References to 30 or less 
    Restricts the number of Reference Transforms to 5 or less 
    Forbids the use of MD5 related signature or mac algorithms 
    Ensures that Reference Ids are unique to help prevent signature wrapping attacks 
    Forbids Reference URIs of type http, https or file 
    Does not allow a RetrievalMethod to reference another RetrievalMethod 
    Forbids RSA or DSA keys less than 1024 bits 

In addition, the jdk.xml.dsig.secureValidationPolicy security property can be used to control and fine-tune the restrictions above or add additional restrictions. See the definition of the property in the java.security file for more information.