v0.0.12: Encrypted backup/restore + history module

Protocol:
- history.rs: derive_history_key (HKDF from seed, info="warzone-history")
- encrypt_history / decrypt_history (ChaCha20-Poly1305, WZH1 magic)
- 2 new tests (roundtrip + wrong seed), total 19/19

CLI:
- `warzone backup [output.wzb]` — exports all sessions + pre-keys
  as encrypted blob (only your seed can decrypt)
- `warzone restore <input.wzb>` — imports backup, merges (no overwrite)
- Backup format: WZH1 magic + nonce + encrypted JSON

Storage:
- export_all() — dumps sessions + pre-keys as base64 JSON
- import_all() — merges backup data (skip existing entries)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

warzone/crates/warzone-protocol/src/history.rs

@@ -0,0 +1,58 @@
+//! Encrypted message history: backup and restore.
+//!
+//! History key derived from seed via HKDF (info="warzone-history").
+//! Format: MAGIC(4) + nonce(12) + ciphertext (ChaCha20-Poly1305).
+
+use crate::crypto::{aead_decrypt, aead_encrypt, hkdf_derive};
+use crate::errors::ProtocolError;
+
+const HISTORY_MAGIC: &[u8; 4] = b"WZH1";
+
+/// Derive history encryption key from seed.
+pub fn derive_history_key(seed: &[u8; 32]) -> [u8; 32] {
+    let derived = hkdf_derive(seed, b"", b"warzone-history", 32);
+    let mut key = [0u8; 32];
+    key.copy_from_slice(&derived);
+    key
+}
+
+/// Encrypt a history blob (JSON messages serialized to bytes).
+pub fn encrypt_history(seed: &[u8; 32], plaintext: &[u8]) -> Vec<u8> {
+    let key = derive_history_key(seed);
+    let encrypted = aead_encrypt(&key, plaintext, HISTORY_MAGIC);
+    let mut result = Vec::with_capacity(4 + encrypted.len());
+    result.extend_from_slice(HISTORY_MAGIC);
+    result.extend_from_slice(&encrypted);
+    result
+}
+
+/// Decrypt a history blob.
+pub fn decrypt_history(seed: &[u8; 32], data: &[u8]) -> Result<Vec<u8>, ProtocolError> {
+    if data.len() < 4 || &data[..4] != HISTORY_MAGIC {
+        return Err(ProtocolError::DecryptionFailed);
+    }
+    let key = derive_history_key(seed);
+    aead_decrypt(&key, &data[4..], HISTORY_MAGIC)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn roundtrip() {
+        let seed = [42u8; 32];
+        let messages = b"[{\"from\":\"alice\",\"text\":\"hello\"}]";
+        let encrypted = encrypt_history(&seed, messages);
+        let decrypted = decrypt_history(&seed, &encrypted).unwrap();
+        assert_eq!(decrypted, messages);
+    }
+
+    #[test]
+    fn wrong_seed_fails() {
+        let seed = [42u8; 32];
+        let wrong = [99u8; 32];
+        let encrypted = encrypt_history(&seed, b"secret");
+        assert!(decrypt_history(&wrong, &encrypted).is_err());
+    }
+}

warzone/crates/warzone-protocol/src/lib.rs

@@ -9,3 +9,4 @@ pub mod ratchet;
 pub mod message;
 pub mod session;
 pub mod store;
+pub mod history;