lhotari opened a new pull request, #25400:
URL: https://github.com/apache/pulsar/pull/25400

   ### Motivation
   
   Java Cryptography Architecture (JCA) classes like `Cipher`, `MessageDigest`, 
`KeyGenerator`, `CertificateFactory`, etc. are **not thread-safe** per 
[Oracle's Java PKI Programmer's 
Guide](https://docs.oracle.com/en/java/javase/21/security/java-pki-programmers-guide.html).
 Sharing instances across threads without synchronization can cause corrupted 
output, `BadPaddingException`, or silently wrong cryptographic results.
   
   This was confirmed by Netty's [PR 
#16350](https://github.com/netty/netty/pull/16350) for `CertificateFactory`, 
and is well-documented for `MessageDigest` 
([pmd/pmd#1862](https://github.com/pmd/pmd/issues/1862)), `Cipher` 
([ekino/hibernate-crypto-types#14](https://github.com/ekino/hibernate-crypto-types/issues/14)),
 and `KeyGenerator`.
   
   A review of the Pulsar codebase identified the following thread-safety 
issues:
   
   **MessageCryptoBc (HIGH):**
   - `Cipher cipher` instance field (line 100) — `encrypt()` is `synchronized` 
but `decrypt()`/`decryptData()` are not, so the shared Cipher can be used 
concurrently from different threads
   - `MessageDigest digest` instance field (line 101) — used in 
`decryptDataKey()` and `getKeyAndDecryptData()` without any synchronization
   - `static KeyGenerator keyGenerator` (line 97) — shared across ALL 
instances, written from constructors on different threads with only 
per-instance synchronization
   
   **DefaultRoleAnonymizerType (MEDIUM-HIGH):**
   - `MessageDigest digest` fields in `SHA256` and `MD5` enum singletons — 
`anonymize()` called concurrently without synchronization; 
`MessageDigest.digest()` resets internal state, so concurrent use produces 
corrupted hashes
   
   **SecurityUtility (LOW):**
   - `static List<KeyFactory> KEY_FACTORIES` — cached instances shared across 
threads. While likely safe in practice for standard JDK implementations, the 
API contract doesn't guarantee thread-safety.
   
   ### Modifications
   
   **MessageCryptoBc:** Replaced shared `Cipher`, `MessageDigest`, and 
`KeyGenerator` fields with `FastThreadLocal`-cached instances. This is a hot 
path (per-message encrypt/decrypt), so thread-local caching avoids the cost of 
creating new instances per call while ensuring thread safety.
   
   **DefaultRoleAnonymizerType:** Replaced `MessageDigest` instance fields in 
enum singletons with `FastThreadLocal`-cached instances. This is a hot path 
when enabled (called for every authentication role logged).
   
   **SecurityUtility:** Removed cached static `KeyFactory` instances. New 
instances are created per call in `loadPrivateKeyFromPemStream()`. This is not 
a hot path (only used during TLS key loading at connection setup), so caching 
is unnecessary.
   
   ### Verifying this change
   
   - [ ] Make sure that the change passes the CI checks.
   
   This change is already covered by existing tests, such as:
   - `MessageCryptoBc` unit tests in `pulsar-client-messagecrypto-bc`
   - `DefaultRoleAnonymizerType` tests in `pulsar-broker-common`
   - `SecurityUtility` tests in `pulsar-common`
   - End-to-end encryption integration tests like 
`SimpleProducerConsumerTest#testCryptoWithChunking`
   
   ### Does this pull request potentially affect one of the following parts:
   
   - [ ] Dependencies (add or upgrade a dependency)
   - [ ] The public API
   - [ ] The schema
   - [ ] The default values of configurations
   - [x] The threading model
   - [ ] The binary protocol
   - [ ] The REST endpoints
   - [ ] The admin CLI options
   - [ ] The metrics
   - [ ] Anything that affects deployment
   
   ### Documentation
   
   - [x] `doc-not-needed`
   
   ### Matching PR in forked repository
   
   PR in forked repository: <!-- ENTER URL HERE -->


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