DO NOT REPLY [Bug 49465] New: impossible to subclass XMLCipher

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https://issues.apache.org/bugzilla/show_bug.cgi?id=49465

           Summary: impossible to subclass XMLCipher
           Product: Security
           Version: unspecified
          Platform: PC
        OS/Version: Windows NT
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Encryption
        AssignedTo: security-dev@xml.apache.org
        ReportedBy: Clement_Pellerin@ibi.com


Created an attachment (id=25614)
 --> (https://issues.apache.org/bugzilla/attachment.cgi?id=25614)
source code patch and new junit

The constructor of XMLCipher is private which makes it impossible to subclass
XMLCipher. Furthermore, much of the work to construct the XMLCipher instance is
located in the getInstance() or getProviderInstance() methods. That would force
a subclass to duplicate that code once again.

The goal of this effort is to experiment with per KeyInfo KeyResolvers to
resolve the Key Encryption Key dynamically based on the EncryptedKey/KeyInfo
carried in the message. The junit in attachment shows how to achieve it through
subclassing. This might not be the most obvious use of the API, but at least it
proves that it can be done. It has the advantage that none of the API changes
are controversial.

The solution involves:
- Making the XMLCipher constructor protected. Callers must still call one of
the getInstance() or getProviderInstance() methods.
- pushing all the construction code in getInstance() and getProviderInstance()
into the real constructor.
- relaxing the requirement that provider must not be null. Passing null for the
provider in getProviderInstance() gives the same result as using the equivalent
getInstance() method.
- Adding createKeyInfo() and createEncryptedKeyResolver() factory methods in
XMLCipher.
- Changing XMLCipher to use the new factory methods when creating internal
KeyInfo or EncryptedKeyResolver objects.
- Adding the method createXMLCipher() to EncryptedKeyResolver.
- Also added some test to @return keywords that were empty in XMLCipher

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DO NOT REPLY [Bug 49465] impossible to subclass XMLCipher

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https://issues.apache.org/bugzilla/show_bug.cgi?id=49465

--- Comment #3 from coheigea <co...@apache.org> 2010-10-12 12:30:29 EDT ---

Thanks for the patch....I committed some of the changes you suggested for
XMLCipher, namely cleaning up the constructor and getInstance methods, as well
as various spelling corrections for the Javadoc. 

Author: coheigea
Date: Tue Oct 12 16:24:15 2010
New Revision: 1021829

URL: http://svn.apache.org/viewvc?rev=1021829&view=rev
Log:
Committed some of the improvements to XMLCipher as suggested in BUG 49465 - 
impossible to subclass XMLCipher.

Modified:
   santuario/trunk/CHANGELOG.txt
   santuario/trunk/src/org/apache/xml/security/encryption/XMLCipher.java


Thanks,

Colm.

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DO NOT REPLY [Bug 49465] impossible to subclass XMLCipher

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https://issues.apache.org/bugzilla/show_bug.cgi?id=49465

--- Comment #1 from sean.mullan@oracle.com 2010-09-30 14:58:04 EDT ---
I only skimmed the patch but it seems to me a much simpler approach would be to
add a new overloaded XMLCipher.init method that takes a KeyResolver instead of
a Key. Did you consider that solution?

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DO NOT REPLY [Bug 49465] impossible to subclass XMLCipher

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https://issues.apache.org/bugzilla/show_bug.cgi?id=49465

--- Comment #2 from Clement Pellerin <Cl...@ibi.com> 2010-09-30 16:54:39 EDT ---
I agree subclassing does not fit the design of the static factory methods
XMLCipher.getInstance(). There is bound to be a better solution if we can
consider more visible changes to the API.

Your suggestion is promising but not sufficient in itself.

The essence of the problem occurs in
EncryptedKeyResolver.engineLookupAndResolveSecretKey():
            XMLCipher cipher = XMLCipher.getInstance();
            cipher.init(XMLCipher.UNWRAP_MODE, _kek);
This XMLCipher object is created internally.
The user does not control its options.
We need to attach the KeyResolvers from the outer XMLCipher into this one.
Usually this is done by registering the KeyResolvers globally.
The whole point of my effort is to allow different KeyResolvers on
different XMLCipher objects so this is not applicable.

An elegant solution would be to pass a context around but
we are not designing JSR-106 from scratch here.

A possible solution would be to pass the outer XMLCipher in the
EncryptedKeyResolver when it is created in XMLCipher.decryptToByteArray()
This is the code that needs modifications:
            ki.registerInternalKeyResolver(
                new EncryptedKeyResolver(
                            encryptedData.getEncryptionMethod().getAlgorithm(), 
                            _kek));
Then we could pass the outer XMLCipher KeyResolvers to the inner XMLCipher
inside EncryptedKeyResolver.

This is a simplified view since XMLCipher does not hold
the KeyResolvers directly. Instead, the KeyResolvers are added
to KeyInfo with the call KeyInfo.registerInternalKeyResolver().

Whatever the final solution becomes, I still think the clean up of
the XMLCipher constructor and getInstance() methods stands on its own
(if we keep the constructor private).

Let's continue the discussion to discover what could be the
best solution with reasonable changes to the public API.

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