RFR: 8353578: Refactor existing usage of internal HKDF impl to use the KDF API

[Bradford Wetmore]

On Thu, 3 Apr 2025 00:51:44 GMT, Valerie Peng <valeriep at openjdk.org> wrote:

>> src/java.base/share/classes/sun/security/ssl/KAKeyDerivation.java line 120:
>> 
>>> 118:                 SecretKey earlySecret = hkdf.deriveKey("TlsEarlySecret",
>>> 119:                         HKDFParameterSpec.ofExtract().addSalt(zeros)
>>> 120:                         .addIKM(ikm).extractOnly());
>> 
>> Maybe no need for `addSalt(zeros)`. I remember salt is by default zeros for HKDF.
>
> Yes, I am on the fence about this. Given the specified value is the same as the default, it can be removed. I kept it there so the new code matches the original code completely. Not much difference either way I think.

I like having it there to communicate that is really the intent.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24393#discussion_r2029534765