RFR: 8368984: Extra slashes in Cipher transformation leads to NSPE instead of NSAE

[Weijun Wang]

On Thu, 2 Oct 2025 23:14:48 GMT, Valerie Peng <valeriep at openjdk.org> wrote:

> This PR updates the cipher transformation parsing and verification logic to be stricter and throws NoSuchAlgorithmException (NSAE) when additional slash(es) is found. With the existing parsing logic, the extra slash(es) is likely to end up in the last component, i.e. the padding scheme, and lead to NoSuchPaddingException (NSPE) from the underlying CipherSpi object. 
> 
> Out of the supported cipher algorithms for all JDK providers, PBES2 cipher algorithms and RSA cipher with OAEP paddings may contain truncated SHA-512 in their transformations. This proposed fix would check for truncated SHA in both algorithm and padding schemes and throws NSAE if any extra slash is found. 
> 
> Thanks in advance for the review~

src/java.base/share/classes/javax/crypto/Cipher.java line 329:

> 327:                     SHA512TRUNCATED.length());
> 328:             sha512SlashIdx = (sha512Idx != -1 ? sha512Idx + 3 : -2);
> 329:         }

The logic is quite complex. Can you create a dedicated method for it like `indexOfRealSlashIn(String s)`?

Also, although we know there is no `512/2` in valid `mode`, there is no need to treat it specially, especially if we have `indexOfReachSlashIn`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27615#discussion_r2400611322