RFR: 8358159: Empty mode/padding in cipher transformations [v3]

[Valerie Peng]

On Wed, 4 Jun 2025 10:37:28 GMT, Varada M <varadam at openjdk.org> wrote:

>> Omitting the mode/padding in a transformation string eg: "AES/ /NoPadding" throws NoSuchAlgorithmException.
>> This patch restores the behavior by ensuring that empty mode or padding strings are interpreted as null.
>> 
>> Testing done for : tier1 - fastdebug level (AIX)
>> 
>> JBS: [JDK-8358159](https://bugs.openjdk.org/browse/JDK-8358159)
>
> Varada M has updated the pull request incrementally with one additional commit since the last revision:
> 
>   whitespace error fix

src/java.base/share/classes/javax/crypto/Cipher.java line 393:

> 391:             this.suffix = suffix.toUpperCase(Locale.ENGLISH);
> 392:             this.mode = ((mode == null) || mode.isEmpty()) ? null : mode;
> 393:             this.pad = ((pad == null) || pad.isEmpty()) ? null : pad;

Thanks for reporting and fixing this issue. 
Since this is an internal class used solely inside `Cipher` class, instead of changing the empty string to null inside the `Transform` constuctor, we can do that before calling `Transform` constructor. Also if one of `mode` or `pad` is empty, then maybe we don't need all 4 `Transform`s.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25547#discussion_r2127160213