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asmhatreandClaude Sonnet 5.5 eca73ad544 Add kdf module: Key Derivation Function API (JEP 510, final in JDK 25), HKDF, RFC 5869 vectors, interop with Python cryptography and openssl, per-tenant keys

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b7rnC7jppGGdHGESvy

2026-10-28 18:07:57 +00:00

interop

Add kdf module: Key Derivation Function API (JEP 510, final in JDK 25), HKDF, RFC 5869 vectors, interop with Python cryptography and openssl, per-tenant keys

2026-10-28 18:07:57 +00:00

output

Add kdf module: Key Derivation Function API (JEP 510, final in JDK 25), HKDF, RFC 5869 vectors, interop with Python cryptography and openssl, per-tenant keys

2026-10-28 18:07:57 +00:00

src

Add kdf module: Key Derivation Function API (JEP 510, final in JDK 25), HKDF, RFC 5869 vectors, interop with Python cryptography and openssl, per-tenant keys

2026-10-28 18:07:57 +00:00

README.md

Add kdf module: Key Derivation Function API (JEP 510, final in JDK 25), HKDF, RFC 5869 vectors, interop with Python cryptography and openssl, per-tenant keys

2026-10-28 18:07:57 +00:00

run.sh

Add kdf module: Key Derivation Function API (JEP 510, final in JDK 25), HKDF, RFC 5869 vectors, interop with Python cryptography and openssl, per-tenant keys

2026-10-28 18:07:57 +00:00

README.md

kdf

Companion code for the ankurm.com article Key Derivation Function API in Java (JEP 510): HKDF Explained with Real Examples.

javax.crypto.KDF was a preview API in JDK 24 (JEP 478) and is final in JDK 25 (JEP 510): no --enable-preview. The JDK ships exactly three algorithms, all HKDF (RFC 5869), all from the SunJCE provider: HKDF-SHA256, HKDF-SHA384, HKDF-SHA512. Everything here ran on Temurin 25.0.5+8; no dependencies except the comparison tools (Python cryptography 50.0.1 and the openssl 3.0.13 command line) for the interop steps.

File	What it shows	Output
(script)	`javap` of `KDF`, `KDFParameters`, `KDFSpi`, `HKDFParameterSpec` and its nested types; proof it is not a preview API	`output/01-api-shape.txt`
`src/ApiTour.java`	registered algorithms, `getInstance` failures, the three spec shapes (extract+expand, extract only, expand only), several IKM pieces, `deriveKey` vs `Cipher.init` key sizes	`output/02-api-tour.txt`
`src/Rfc5869Vectors.java`	RFC 5869 appendix A cases 1 to 3 (SHA-256) asserted three ways each: OKM, PRK, expand-only from the PRK	`output/03-rfc5869-vectors.txt`
`src/RefHkdf.java`, `src/RefCheck.java`, `src/Interop.java`, `interop/cases.tsv`	HKDF written by hand from the RFC with `javax.crypto.Mac`, checked against the RFC, then JDK vs hand-written vs Python `cryptography` on 300 generated cases (SHA-256/384/512)	`output/04-interop-java-vs-python-vs-reference.txt`
`interop/gen_cases.py`, `interop/openssl_check.py`	how `cases.tsv` was made (fixed seed, regenerates byte-identically) and a third opinion from `openssl kdf`	`output/05-interop-python-openssl.txt`
`src/Tenants.java`	per-tenant, per-purpose, per-version keys from one master key; length-prefixed `info`; AES-GCM isolation	`output/06-tenants.txt`
`src/Mistakes.java`	same `info` twice, ambiguous concatenation, salt facts, the 255 x HashLen limit, a 4-digit PIN through HKDF vs PBKDF2	`output/07-mistakes.txt`

JDK25=/path/to/jdk-25 ./run.sh     # needs python3 with `cryptography`, and openssl, for output/05

The demos assert as they go (PASS/FAIL lines, non-zero exit on failure), following the other standalone modules in this repo; there is no JUnit here. Output is byte-stable. Not reproduced: JDK 24's preview behaviour (no JDK 24 was installed), and openssl was only run with 3.0.13.