Just An Application

August 22, 2014

And Another One: Part Twenty Two — The Actual Fix

And after all that, how has it actually been fixed ?

Like this apparently, at least in the short term.

    Add API to check certificate chain signatures
    
    Add hidden API to check certificate chain signatures when needed. The
    getCertificates implementation returns a list of all the certificates and
    chains and would expect any caller interested in verifying actual chains
    to call getCodeSigners instead.
    
    We add this hidden constructor as a stop-gap until we can switch callers
    over to getCodeSigners.

The implication of the above is that the long term fix is for the PackageParser loadCertificates method to call the JarEntry getCodeSigners method rather than the getCertificates method as it does now.

The getCodeSigners method is declared like this

    public CodeSigner[] getCodeSigners()

On its own this is not going to achieve anything since getCodeSigners does exactly the same amount of certificate chain verification as the original version of getCertificates, i.e., none.

What it does do is package the certificates up into instances of java.security.CodeSigner for you.

A CodeSigner contains a java.security.cert.CertPath.

Once you have one of those you can either validate the certificates in it yourself or hand the whole thing to a
java.security.cert.CertPathValidator who will do it for you, assuming you can work out how to set up the right CertPathParameters instance.

And after all that and assuming everything verifies you can collect all the constituent Certificates together and then turn them into Signatures just like before.

An alternative long term solution might be to come up with a proper Application Signature abstraction and a proper Security Policy abstraction.

Then, rather have random bits of code deciding to implement ad hoc security policies because they can get at the internals of Signatures, they would have to use the Security Policy !


Copyright (c) 2014 By Simon Lewis. All Rights Reserved.

Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and owner Simon Lewis is strictly prohibited.

Excerpts and links may be used, provided that full and clear credit is given to Simon Lewis and justanapplication.wordpress.com with appropriate and specific direction to the original content.

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