RFR: 8331008: Implement JEP 478: Key Derivation Function API (Preview) [v22]

[Kevin Driver]

On Thu, 5 Sep 2024 17:39:56 GMT, Kevin Driver <kdriver at openjdk.org> wrote:

>> src/java.base/share/classes/com/sun/crypto/provider/HkdfKeyDerivation.java line 358:
>> 
>>> 356:         }
>>> 357: 
>>> 358:         return Arrays.copyOf(kdfOutput, outLen);
>> 
>> Here is an alternative solution which does not need `Arrays.copyOf()` call:
>> Suggestion:
>> 
>>         kdfOutput = new byte[outLen];
>>         int i = 0;
>>         int offset = 0;
>>         try {
>>             while (i < rounds) {
>>                 if (i > 0) {
>>                     hmacObj.update(kdfOutput, offset - hmacLen, hmacLen); // add T(i-1)
>>                 }
>>                 hmacObj.update(info);                   // Add info
>>                 hmacObj.update((byte) ++i);             // Add round number
>>                 if (i == rounds && (outLen - offset < hmacLen)) {
>>                     // special handling for last chunk
>>                     byte[] tmp = hmacObj.doFinal();
>>                     System.arraycopy(tmp, 0, kdfOutput, offset,
>>                             outLen - offset);
>>                     offset = outLen;
>>                 } else {
>>                     hmacObj.doFinal(kdfOutput, offset);
>>                     offset += hmacLen;
>>                 }
>>             }
>>         } catch (ShortBufferException sbe) {
>>             // This really shouldn't happen given that we've
>>             // sized the buffers to their largest possible size up-front,
>>             // but just in case...
>>             throw new RuntimeException(sbe);
>>         }
>>         return kdfOutput;
>
> My personal opinion is that this adds complexity which is unnecessary. The `Arrays.copyOf` solution reads more simply and GC will take care of any extra allocation once it goes out of scope. I appreciate the alternate fix, but in this case the original solution is more easily understood and thus more maintainable.

Made a couple small changes and accepted your proposed code. Thanks!

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PR Review Comment: https://git.openjdk.org/jdk/pull/20301#discussion_r1746247893