feat: Introduce signed, verifiable entries with protobuf definitions, cryptographic signing, and hashing, updating the data model and architecture.

lattice-core/src/node.rs

@@ -1,7 +1,28 @@
 //! Node identity and cryptographic keys
+//!
+//! Each node has an Ed25519 keypair:
+//! - Private key: stored locally in `identity.key` (never replicated)
+//! - Public key: serves as the node's identity (32 bytes)
 
-use ed25519_dalek::{SigningKey, VerifyingKey};
+use ed25519_dalek::{Signature, Signer, SigningKey, Verifier, VerifyingKey};
 use rand::rngs::OsRng;
+use std::fs;
+use std::io::{self, Read, Write};
+use std::path::Path;
+use thiserror::Error;
+
+/// Errors that can occur during node operations
+#[derive(Error, Debug)]
+pub enum NodeError {
+    #[error("IO error: {0}")]
+    Io(#[from] io::Error),
+    
+    #[error("Invalid key length: expected 32 bytes, got {0}")]
+    InvalidKeyLength(usize),
+    
+    #[error("Invalid signature")]
+    InvalidSignature,
+}
 
 /// A node in the Lattice mesh.
 ///
@@ -18,13 +39,177 @@ impl Node {
         Self { signing_key }
     }
 
+    /// Create a node from an existing signing key.
+    pub fn from_signing_key(signing_key: SigningKey) -> Self {
+        Self { signing_key }
+    }
+
+    /// Load a node's identity from a key file, or generate and save if it doesn't exist.
+    pub fn load_or_generate(path: impl AsRef<Path>) -> Result<Self, NodeError> {
+        let path = path.as_ref();
+        if path.exists() {
+            Self::load(path)
+        } else {
+            let node = Self::generate();
+            node.save(path)?;
+            Ok(node)
+        }
+    }
+
+    /// Load a node's identity from a key file.
+    pub fn load(path: impl AsRef<Path>) -> Result<Self, NodeError> {
+        let mut file = fs::File::open(path)?;
+        let mut bytes = Vec::new();
+        file.read_to_end(&mut bytes)?;
+        
+        if bytes.len() != 32 {
+            return Err(NodeError::InvalidKeyLength(bytes.len()));
+        }
+        
+        let key_bytes: [u8; 32] = bytes.try_into().unwrap();
+        let signing_key = SigningKey::from_bytes(&key_bytes);
+        Ok(Self { signing_key })
+    }
+
+    /// Save the node's private key to a file.
+    pub fn save(&self, path: impl AsRef<Path>) -> Result<(), NodeError> {
+        let path = path.as_ref();
+        
+        // Create parent directories if they don't exist
+        if let Some(parent) = path.parent() {
+            fs::create_dir_all(parent)?;
+        }
+        
+        let mut file = fs::File::create(path)?;
+        file.write_all(self.signing_key.as_bytes())?;
+        Ok(())
+    }
+
     /// Get the node's public key (identity).
     pub fn public_key(&self) -> VerifyingKey {
         self.signing_key.verifying_key()
     }
 
+    /// Get the node's public key as bytes (32 bytes).
+    pub fn public_key_bytes(&self) -> [u8; 32] {
+        self.signing_key.verifying_key().to_bytes()
+    }
+
     /// Get the signing key for creating signatures.
     pub fn signing_key(&self) -> &SigningKey {
         &self.signing_key
     }
+
+    /// Sign a message.
+    pub fn sign(&self, message: &[u8]) -> Signature {
+        self.signing_key.sign(message)
+    }
+
+    /// Verify a signature against this node's public key.
+    pub fn verify(&self, message: &[u8], signature: &Signature) -> Result<(), NodeError> {
+        self.public_key()
+            .verify(message, signature)
+            .map_err(|_| NodeError::InvalidSignature)
+    }
+
+    /// Verify a signature using a raw public key.
+    pub fn verify_with_key(
+        public_key: &VerifyingKey,
+        message: &[u8],
+        signature: &Signature,
+    ) -> Result<(), NodeError> {
+        public_key
+            .verify(message, signature)
+            .map_err(|_| NodeError::InvalidSignature)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::env::temp_dir;
+
+    #[test]
+    fn test_generate() {
+        let node = Node::generate();
+        let pk = node.public_key_bytes();
+        assert_eq!(pk.len(), 32);
+    }
+
+    #[test]
+    fn test_sign_and_verify() {
+        let node = Node::generate();
+        let message = b"hello lattice";
+        
+        let signature = node.sign(message);
+        assert!(node.verify(message, &signature).is_ok());
+    }
+
+    #[test]
+    fn test_verify_wrong_message() {
+        let node = Node::generate();
+        let signature = node.sign(b"original");
+        
+        assert!(node.verify(b"tampered", &signature).is_err());
+    }
+
+    #[test]
+    fn test_verify_with_different_key() {
+        let node1 = Node::generate();
+        let node2 = Node::generate();
+        
+        let signature = node1.sign(b"message");
+        assert!(node2.verify(b"message", &signature).is_err());
+    }
+
+    #[test]
+    fn test_save_and_load() {
+        let temp_path = temp_dir().join("lattice_test_identity.key");
+        
+        // Generate and save
+        let node1 = Node::generate();
+        let pk1 = node1.public_key_bytes();
+        node1.save(&temp_path).unwrap();
+        
+        // Load and verify same key
+        let node2 = Node::load(&temp_path).unwrap();
+        let pk2 = node2.public_key_bytes();
+        
+        assert_eq!(pk1, pk2);
+        
+        // Cleanup
+        fs::remove_file(&temp_path).ok();
+    }
+
+    #[test]
+    fn test_load_or_generate() {
+        let temp_path = temp_dir().join("lattice_test_identity2.key");
+        
+        // Remove if exists
+        fs::remove_file(&temp_path).ok();
+        
+        // First call: generates
+        let node1 = Node::load_or_generate(&temp_path).unwrap();
+        let pk1 = node1.public_key_bytes();
+        
+        // Second call: loads existing
+        let node2 = Node::load_or_generate(&temp_path).unwrap();
+        let pk2 = node2.public_key_bytes();
+        
+        assert_eq!(pk1, pk2);
+        
+        // Cleanup
+        fs::remove_file(&temp_path).ok();
+    }
+
+    #[test]
+    fn test_verify_with_key_static() {
+        let node = Node::generate();
+        let pk = node.public_key();
+        let message = b"test message";
+        
+        let signature = node.sign(message);
+        
+        assert!(Node::verify_with_key(&pk, message, &signature).is_ok());
+    }
 }