RFR: 8341346: Add support for exporting TLS Keying Material [v7]

[Bradford Wetmore]

On Wed, 7 May 2025 16:28:27 GMT, Weijun Wang <weijun at openjdk.org> wrote:

>> Bradford Wetmore has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Updated to use the upcoming KDF (still in preview) + bits of JDK-8353578 for compilation)
>
> src/java.base/share/classes/sun/security/ssl/SSLSessionImpl.java line 1694:
> 
>> 1692: 
>> 1693:                     // ...now the final expand.
>> 1694:                     SecretKey key = hkdf.deriveKey(label,
> 
> PKCS #11 is picky about key algorithm names and I'm not sure if `label` is always accepted. The KDF API has the algorithm in the method arguments so it's left to user to specify one. I'm not sure how the export keying material will be used. If it is used in encryption, the algorithm may need to be something like "AES".

IIUC, the exported keying material can be used for any purpose or algorithm, so we really can't make an good educated guess what it might be.  They could be Keys (Ciphers), byte array/value challenges, or even just data that will be signed.  This is just doing a quick read of some of the IANA definitions which link to some of the known use cases:

    https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#exporter-labels 

Thus the type needs to be something generic.  The label sounded good initially, but there is no specific prohibition against non-null/empty label in the TLS Exporters, but KDF prohibits null/empty labels.

Maybe a label like "ExportKeyingMaterial"?

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PR Review Comment: https://git.openjdk.org/jdk/pull/24976#discussion_r2078948256