RFR: 8331008: Implement JEP 478: Key Derivation Function API (Preview) [v11]

[Valerie Peng]

On Fri, 16 Aug 2024 19:29:36 GMT, Kevin Driver <kdriver at openjdk.org> wrote:

>> src/java.base/share/classes/com/sun/crypto/provider/HkdfKeyDerivation.java line 369:
>> 
>>> 367:                 throw new RuntimeException(sbe);
>>> 368:             }
>>> 369:         }
>> 
>> `tLength` may not be necessary. Variables only used inside the loop can also be moved to the loop.
>> The loop can be modified as:
>> 
>> 
>> for (int i = 0, offset = 0; i < rounds; i++, offset += hmacLen) {
>>             // Calculate this round
>>             try {
>>                 if (i > 0) {
>>                     hmacObj.update(kdfOutput, offset - hmacLen, hmacLen); // add T(i-1)
>>                 }
>>                 hmacObj.update(info);                       // Add info
>>                 hmacObj.update((byte) (i + 1));             // Add round number
>>                 hmacObj.doFinal(kdfOutput, offset);
>>             } 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);
>>             }
>>         }
>
> I'll need to double-check the logic of this snippet. For example, in the first iteration of the loop, isn't `tLength` == 0? Yet, you have it always set to `hmacLen`.

Sure, I added an if-check to skip the `hmacObj.update(...)` call for the i=0 case. This way, you don't need to set `tLength` to 0 and then changing it to `hmacLen` afterwards. I find it easier to understand.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20301#discussion_r1724130421