# Deterministic HMAC fixture

Pinned input/output triple for the `AsbSystemAuthenticator.Sign`
crypto path, captured from the .NET reference. Used by the Rust
parity test in `crates/mxaccess-asb-nettcp/tests/deterministic_hmac.rs`
to assert byte-equality of crypto_key derivation, canonical XML
emission, HMAC-SHA1, PBKDF2-SHA1 AES key derivation, and AES-CBC
encryption — independent of session randomness (DH private key,
remote public key, and AES IV are all pinned to deterministic values
so a single `cargo test` run can reproduce the .NET output).

## Capture procedure

```powershell
dotnet run --project src\MxAsbClient.Probe -c Release -- --dump-deterministic-hmac > capture.txt
```

The probe's `--dump-deterministic-hmac` flag (added 2026-05-05)
inlines the per-step decomposition of `Sign` (`AsbSystemAuthenticator
.cs:62-82`):

1. `shared = remote_pub^private_key mod prime` (.NET `BigInteger.ModPow`)
2. `crypto_key = shared || passphrase_utf8`
3. `xml = AuthenticateMe.ToXml()` with empty MAC + IV
4. `hmac = HMAC-SHA1(crypto_key, utf8(xml))`
5. `aes_key = PBKDF2-SHA1(base64(crypto_key), "ArchestrAService", 1000, 16)`
6. `encrypted_mac = AES-CBC(aes_key, iv=zeros, hmac, padding=PKCS7)`

Step 6 uses an all-zero IV to make the test reproducible — the real
wire path uses a random IV per call, but the Rust test bypasses the
random IV path by calling the AES primitive directly with the same
zero IV.

## File format

Plain-ASCII `key=value` lines, one per line. Hex values are
upper-case (matching .NET's `Convert.ToHexString`). The `xml_utf8_b64`
field encodes the canonical XML as base64 of the UTF-8 bytes.

## Files

- `authenticate-me.kv` — fixture for the `AuthenticateMe` shape with
  the `[XmlType(Namespace="http://asb.contracts.data/20111111")]`
  ConsumerAuthenticationData wrapper.