refactor(core,wasm): zeroized ed25519 seed decode in core; org_unwrap_key reuses it

Review fixes for Task 1 (org_unwrap_key). Public signature unchanged.

- Add device::extract_ed25519_seed -> Zeroizing<[u8;32]>: length-checks the
  slice then copy_from_slice straight into the Zeroizing buffer, so the raw
  seed never lands in a plain [u8;32] (Important #1).
- Refactor device::sign() to call the new helper (pure refactor; device/sign
  roundtrip tests unchanged and green) (Important #2).
- org_unwrap_key now calls relicario_core::device::extract_ed25519_seed
  directly; drop the duplicated local decode_device_seed helper and remove the
  redundant ssh-key dep from relicario-wasm (core already pins it) (Important #2).
- Device-key-form finding (OpenSSH PEM, not base64; spec name matches reality)
  moved onto the core helper, condensed copy kept on org_unwrap_key.
- Test helper keeps the private key as Zeroizing<String> and passes &priv
  (derefs to &str) — no plain-String copy (Minor #3).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014s527M917W47LDrfQ4t47g

crates/relicario-wasm/Cargo.toml

@@ -21,7 +21,6 @@ base64 = "0.22"
 hex = "0.4"
 rand = "0.8"
 once_cell = "1"
-ssh-key = { version = "0.6", features = ["ed25519", "std"] }
 
 [dev-dependencies]
 wasm-bindgen-test = "0.3"

crates/relicario-wasm/src/lib.rs

@@ -570,42 +570,20 @@ pub fn wasm_unwrap_recovery_qr(
 
 // ── Org vault WASM bridge ────────────────────────────────────────────────────
 
-/// Decode an OpenSSH ed25519 private key string into a Zeroizing 32-byte seed.
-///
-/// **Key-form finding (Step 1 of the task brief):**
-/// `relicario_core::device::generate_keypair()` returns the private key as an
-/// OpenSSH PEM blob — the multiline `-----BEGIN OPENSSH PRIVATE KEY-----...` format,
-/// the same form the `ssh_key` crate emits via `PrivateKey::to_openssh()`. It is
-/// NOT a raw-bytes base64 string. The plan's `device_private_key_base64` parameter
-/// name is therefore misleading; the spec name `device_private_openssh` matches
-/// reality. The SW stores this blob in WASM `DEVICE_STATE` and never exposes it
-/// to JS. If it were ever serialised for cross-session persistence (future work),
-/// it would travel as this same PEM string.
-///
-/// This mirrors the first half of `relicario_core::device::sign()`.
-fn decode_device_seed(private_key_openssh: &str) -> Result<Zeroizing<[u8; 32]>, String> {
-    use ssh_key::PrivateKey;
-    let private = PrivateKey::from_openssh(private_key_openssh)
-        .map_err(|e| format!("parse private key: {e}"))?;
-    let key_data = private
-        .key_data()
-        .ed25519()
-        .ok_or_else(|| "not an ed25519 key".to_string())?;
-    let secret_slice: &[u8] = key_data.private.as_ref();
-    let secret_bytes: [u8; 32] = secret_slice
-        .try_into()
-        .map_err(|_| "invalid ed25519 seed length".to_string())?;
-    let mut seed = Zeroizing::new([0u8; 32]);
-    seed.copy_from_slice(&secret_bytes);
-    Ok(seed)
-}
-
 /// Unwrap a member's ECIES-wrapped org master key into a session handle.
 ///
 /// `keys_blob` is the raw wrapped-key blob at `keys/<member_id>.enc` in the org
 /// repo — produced by `relicario_core::org::wrap_org_key`. `device_private_openssh`
-/// is the device's ed25519 private key in OpenSSH PEM format (held in WASM memory
-/// via `crates/relicario-wasm/src/device.rs`; never exposed to JS).
+/// is the device's ed25519 private key.
+///
+/// **Device-key form (Step 1 finding):** the key arrives as an OpenSSH PEM blob —
+/// the multiline `-----BEGIN OPENSSH PRIVATE KEY-----...` form emitted by
+/// `relicario_core::device::generate_keypair()`, NOT a base64-encoded raw-bytes
+/// string. The plan's `device_private_key_base64` name was misleading; the spec
+/// name `device_private_openssh` matches reality. The SW holds this blob in WASM
+/// `DEVICE_STATE` and never exposes it to JS. Decoding to the zeroized 32-byte
+/// seed is delegated to `relicario_core::device::extract_ed25519_seed`, the same
+/// path `device::sign()` uses, so the secret never lands in a plain `[u8; 32]`.
 ///
 /// The org key is held in the same Zeroizing WASM session registry as the personal
 /// master key; org items share the personal `.enc` AEAD format, so the returned
@@ -615,7 +593,7 @@ pub fn org_unwrap_key(
     keys_blob: &[u8],
     device_private_openssh: &str,
 ) -> Result<SessionHandle, JsError> {
-    let seed = decode_device_seed(device_private_openssh)
+    let seed = relicario_core::device::extract_ed25519_seed(device_private_openssh)
         .map_err(|e| JsError::new(&format!("bad device key: {e}")))?;
     let org_key = relicario_core::org::unwrap_org_key(keys_blob, &seed)
         .map_err(|e| JsError::new(&format!("org unwrap failed: {e}")))?;
@@ -637,10 +615,11 @@ mod org_tests {
     /// NOT base64-encoded raw bytes. The plan parameter name "device_private_key_base64"
     /// is misleading; the spec name "device_private_openssh" matches the actual format.
     /// We call the real generator here (not a hand-rolled helper) so the test exercises
-    /// the exact production key format and cannot silently drift.
-    fn test_device_keypair() -> (String, String) {
+    /// the exact production key format and cannot silently drift. The private key is
+    /// kept in its `Zeroizing<String>` wrapper — never copied into a plain `String`.
+    fn test_device_keypair() -> (String, Zeroizing<String>) {
         let (priv_openssh, pub_openssh) = relicario_core::generate_keypair().unwrap();
-        (pub_openssh, priv_openssh.to_string())
+        (pub_openssh, priv_openssh)
     }
 
     #[test]
@@ -652,6 +631,7 @@ mod org_tests {
         let (pub_openssh, priv_openssh) = test_device_keypair();
         let wrapped = wrap_org_key(&org_key, &pub_openssh).unwrap();
 
+        // &priv_openssh derefs Zeroizing<String> → &str; no plain-String copy.
         let handle = org_unwrap_key(&wrapped, &priv_openssh).unwrap();
         // item_encrypt is native-safe: returns Vec<u8>; JsError is only reachable on
         // the error path, which is not exercised here.