On Fri, 17 Oct 2025 06:52:44 GMT, Shawn M Emery <[email protected]> wrote:
>> src/java.base/share/classes/com/sun/crypto/provider/AES_Crypt.java line 911:
>>
>>> 909: }
>>> 910: sessionK[0] = genRoundKeys(key, rounds);
>>> 911: sessionK[1] = invGenRoundKeys();
>>
>> Given the decryption round keys are somewhat based on the encryption round
>> keys, we could combine these two methods into one, e.g.
>>
>> private static int[][] genRoundKeys(byte[] key, int rounds) {
>> int[][] ks = new int[2][]; // key schedule
>>
>> int wLen = (rounds + 1) * WB;
>> int nk = key.length / WB;
>>
>> // generate the round keys for encryption
>> int[] w = new int[wLen];
>> for (int i = 0, j = 0; i < nk; i++, j+=4) {
>> w[i] = ((key[j] & 0xFF) << 24)
>> | ((key[j + 1] & 0xFF) << 16)
>> | ((key[j + 2] & 0xFF) << 8)
>> | (key[j + 3] & 0xFF);
>> }
>> for (int i = nk; i < wLen; i++) {
>> int tmp = w[i - 1];
>> if (i % nk == 0) {
>> int rW = (tmp << 8) & 0xFFFFFF00 | (tmp >>> 24);
>> tmp = subWord(rW) ^ RCON[(i / nk) - 1];
>> } else if ((nk > 6) && ((i % nk) == WB)) {
>> tmp = subWord(tmp);
>> }
>> w[i] = w[i - nk] ^ tmp;
>> }
>> ks[0] = w;
>>
>> // generate the decryption round keys based on encryption ones
>> int[] dw = new int[wLen];
>> int[] temp = new int[WB];
>>
>> // Intrinsics requires the inverse key expansion to be reverse order
>> // except for the first and last round key as the first two round
>> keys
>> // are without a mix column transform.
>> for (int i = 1; i < rounds; i++) {
>> System.arraycopy(w, i * WB, temp, 0, WB);
>> invMixRKey(temp);
>> System.arraycopy(temp, 0, dw, wLen - (i * WB), WB);
>> }
>> // dw[0...3] <- w[0...3] AND dw[4...7] <- w[(wLen - 4)...(wLen -1)]
>> System.arraycopy(w, 0, dw, 0, WB);
>> System.arraycopy(w, wLen - WB, dw, WB, WB);
>> ks[1] = dw;
>> Arrays.fill(temp, 0);
>>
>> return ks;
>> }
>
> These two methods were only the few that I was able to make that were compact
> and singular in purpose (gen round key, gen inverse round key) code as the
> coding style guidelines espouse. The rest of the methods' construction were
> dictated by performance improvements, where compactness came at the cost of
> interpreter speed.
I did make changes based on your code to eliminate len and updates to variable
names.
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PR Review Comment: https://git.openjdk.org/jdk/pull/27807#discussion_r2441096947
