Rename project to quicnprotochat

crates/quicnprotochat-core/src/identity.rs

@@ -0,0 +1,138 @@
+//! Ed25519 identity keypair for MLS credentials and AS registration.
+//!
+//! # Relationship to the Noise keypair
+//!
+//! The X25519 [`NoiseKeypair`](crate::NoiseKeypair) is the transport-layer
+//! static key used in the Noise_XX handshake. The Ed25519 [`IdentityKeypair`]
+//! is the long-term identity key embedded in MLS `BasicCredential`s. The two
+//! keys serve different roles and must not be confused.
+//!
+//! # Zeroize
+//!
+//! The 32-byte private seed is stored as `Zeroizing<[u8; 32]>`, which zeroes
+//! the bytes on drop. `[u8; 32]` is `Copy + Default` and satisfies zeroize's
+//! `DefaultIsZeroes` constraint, avoiding a conflict with ed25519-dalek's
+//! `SigningKey` zeroize impl.
+//!
+//! # Fingerprint
+//!
+//! A 32-byte SHA-256 digest of the raw public key bytes is used as a compact,
+//! collision-resistant identifier for logging.
+
+use ed25519_dalek::{Signer as DalekSigner, SigningKey, VerifyingKey};
+use openmls_traits::signatures::Signer;
+use openmls_traits::types::{Error as MlsError, SignatureScheme};
+use serde::{Deserialize, Serialize};
+use sha2::{Digest, Sha256};
+use zeroize::Zeroizing;
+
+/// An Ed25519 identity keypair.
+///
+/// Created with [`IdentityKeypair::generate`]. The private signing key seed
+/// is zeroed when this struct is dropped.
+pub struct IdentityKeypair {
+    /// Raw 32-byte private seed — zeroized on drop.
+    ///
+    /// Stored as bytes rather than `SigningKey` to satisfy zeroize's
+    /// `DefaultIsZeroes` bound on `Zeroizing<T>`.
+    seed: Zeroizing<[u8; 32]>,
+    /// Corresponding 32-byte public verifying key.
+    verifying: VerifyingKey,
+}
+
+impl IdentityKeypair {
+    /// Recreate an identity keypair from a 32-byte seed.
+    pub fn from_seed(seed: [u8; 32]) -> Self {
+        let signing = SigningKey::from_bytes(&seed);
+        let verifying = signing.verifying_key();
+        Self {
+            seed: Zeroizing::new(seed),
+            verifying,
+        }
+    }
+
+    /// Return the raw 32-byte private seed (for persistence).
+    pub fn seed_bytes(&self) -> [u8; 32] {
+        *self.seed
+    }
+}
+
+impl IdentityKeypair {
+    /// Generate a fresh random Ed25519 identity keypair.
+    pub fn generate() -> Self {
+        use rand::rngs::OsRng;
+        let signing = SigningKey::generate(&mut OsRng);
+        let verifying = signing.verifying_key();
+        let seed = Zeroizing::new(signing.to_bytes());
+        Self { seed, verifying }
+    }
+
+    /// Return the raw 32-byte Ed25519 public key.
+    ///
+    /// This is the byte array used as `identityKey` in `auth.capnp` calls.
+    pub fn public_key_bytes(&self) -> [u8; 32] {
+        self.verifying.to_bytes()
+    }
+
+    /// Return the SHA-256 fingerprint of the public key (32 bytes).
+    pub fn fingerprint(&self) -> [u8; 32] {
+        let mut hasher = Sha256::new();
+        hasher.update(self.verifying.to_bytes());
+        hasher.finalize().into()
+    }
+
+    /// Reconstruct the `SigningKey` from the stored seed bytes.
+    fn signing_key(&self) -> SigningKey {
+        SigningKey::from_bytes(&self.seed)
+    }
+}
+
+/// Implement the openmls `Signer` trait so `IdentityKeypair` can be passed
+/// directly to `KeyPackage::builder().build(...)` without needing the external
+/// `openmls_basic_credential` crate.
+impl Signer for IdentityKeypair {
+    fn sign(&self, payload: &[u8]) -> Result<Vec<u8>, MlsError> {
+        let sk = self.signing_key();
+        let sig: ed25519_dalek::Signature = sk.sign(payload);
+        Ok(sig.to_bytes().to_vec())
+    }
+
+    fn signature_scheme(&self) -> SignatureScheme {
+        SignatureScheme::ED25519
+    }
+}
+
+impl Serialize for IdentityKeypair {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        serializer.serialize_bytes(&self.seed[..])
+    }
+}
+
+impl<'de> Deserialize<'de> for IdentityKeypair {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        let bytes: Vec<u8> = serde::Deserialize::deserialize(deserializer)?;
+        let seed: [u8; 32] = bytes
+            .as_slice()
+            .try_into()
+            .map_err(|_| serde::de::Error::custom("identity seed must be 32 bytes"))?;
+        Ok(IdentityKeypair::from_seed(seed))
+    }
+}
+
+impl std::fmt::Debug for IdentityKeypair {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let fp = self.fingerprint();
+        f.debug_struct("IdentityKeypair")
+            .field(
+                "fingerprint",
+                &format!("{:02x}{:02x}{:02x}{:02x}…", fp[0], fp[1], fp[2], fp[3]),
+            )
+            .finish_non_exhaustive()
+    }
+}