RFR: 8330842: Support AES CBC with Ciphertext Stealing (CTS) in SunPKCS11 [v3]

[Martin Balao]

On Wed, 5 Jun 2024 01:25:24 GMT, Valerie Peng <valeriep at openjdk.org> wrote:

>> `convertCTSVariant` needs the total output's length to determine the penultimate block size and do the slicing in the `out` array. The assumption here is that `outOfs` has the previously generated output (if any) starting at offset 0. In the CTS case, `k` has all the bytes (potentially) added to the output after flushing `padBuffer` with `C_EncryptUpdate` and all the bytes added after `C_EncryptFinal`.
>
> I understand the meaning of `k`. It seems that the code here assumes `outOfs = 0`, but this may not always be the case when operating on user-supplied output byte array, right?

The code does not assume that `outOfs = 0` but that the content of `out` (between 0 and `outOfs`) is previously generated output of a multi-part operation (not the whole output but one that is multiple of the block size). `outOfs + k` is an offset that we need to know and pass to `convertCTSVariant` for the `out` slicing. @franferrax , do you see possible to determine the penultimate block size from `k` only? (i.e. `int pad = k % blockSize;`) This would be more resilient for handling a user-supplied value.

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PR Review Comment: https://git.openjdk.org/jdk/pull/18898#discussion_r1626870291