v0.0.58 - Added derive verb: HMAC-SHA256(privkey, data) for secp256k1, enabling opaque d-tag derivation via nsigner remote backend without exposing the privkey

README.md

@@ -204,6 +204,7 @@ All verbs take their arguments as positional `params` and their options in a tra
 | `encapsulate`           | ml-kem-768                                    | `<peer_pubkey_hex>`              | `algorithm`                      |
 | `decapsulate`           | ml-kem-768                                    | `<ciphertext_hex>`               | `algorithm`, `index`             |
 | `derive_shared_secret`  | x25519                                        | `<peer_pubkey_hex>`              | `algorithm`, `index`             |
+| `derive`                | secp256k1                                     | `<data>`                         | `algorithm`, `index` (required)  |
 | `encrypt`               | otp                                           | `<plaintext_base64>`             | `algorithm`, `encoding`          |
 | `decrypt`               | otp                                           | `<ciphertext>`                   | `algorithm`, `encoding`          |
 | `nostr_get_public_key`  | secp256k1 (NIP-06)                            | —                                | `nostr_index`, `format`          |
@@ -223,6 +224,7 @@ All verbs take their arguments as positional `params` and their options in a tra
 | `sign` / `verify`          | secp256k1, ed25519, ml-dsa-65, slh-dsa-128s   |
 | `encapsulate` / `decapsulate` | ml-kem-768                                 |
 | `derive_shared_secret`     | x25519                                        |
+| `derive`                   | secp256k1                                     |
 | `encrypt` / `decrypt`      | otp                                           |
 | `get_public_key`           | all key-deriving algorithms                   |
 | `nostr_*`                  | secp256k1 (Nostr protocol)                    |
@@ -340,6 +342,23 @@ Response:
 
 `peer_pubkey_hex` is the peer's 32-byte X25519 public key (64 hex chars). Feed the returned `shared_secret` into your own symmetric cipher (e.g. AES-GCM, ChaCha20-Poly1305).
 
+#### `derive` (secp256k1 HMAC-SHA256)
+
+```json
+{ "id": "10", "method": "derive", "params": [ "<data>", { "algorithm": "secp256k1", "index": 0 } ] }
+```
+
+Response:
+```json
+{ "id": "10", "result": "{\"algorithm\":\"secp256k1\",\"key_id\":\"<16hex>\",\"digest\":\"<64hex>\"}" }
+```
+
+Computes `HMAC-SHA256(privkey, data)` where `privkey` is the secp256k1 private key derived on demand at `(algorithm: "secp256k1", index: N)`. `data` is an arbitrary caller-supplied UTF-8 string. Returns the 32-byte digest as 64 lowercase hex chars.
+
+`index` is **required** (no default) — forces conscious selection of which derived key to use as the HMAC key. Omitting it returns `missing_index`.
+
+This is a generic key-derived MAC primitive. Callers domain-separate by prefixing their own label into `data` (e.g. `"myapp/identifier-v1:<path>"`). The private key never leaves the signer; only the digest is returned. Use cases include deterministic, per-user, opaque identifiers for NIP-33 parameterized-replaceable events (e.g. bookmark folder `d` tags) where the same logical name must produce the same `d` tag across devices.
+
 #### `encrypt` / `decrypt` (OTP)
 
 ```json