feat(companion): backup envelope + NIP-46 signer crypto in the native core

Extends archy-fips-core with the two companion-release features' crypto (#128, #139), same JNI-over-JSON contract as the mesh surface: backup.rs — the ADR-005 encrypted-backup envelope, byte-compatible with the node's backup code (Argon2id default params + ChaCha20-Poly1305, blob = base64(salt||nonce||ct)); decrypt ignores extra envelope fields so node backups read here too. Round-trip, tamper, wrong-passphrase and cross-shape tests included. nostr.rs — the phone-side remote-signer crypto: nsec/npub bech32 keys, BIP340 schnorr event signing (NIP-01 id serialization), NIP-44 v2 payloads (HKDF-SHA256 + ChaCha20 + HMAC-SHA256, both padding prefixes), NIP-04 fallback, nostrconnect:// parsing with repeated relay params. Verified against the official NIP-44 vectors (conversation keys, message keys, padded lengths, byte-exact encrypt vectors), the BIP-340 reference sign vectors, and round-trip/tamper/failure tests. secp256k1 0.29 note: Keypair::public_key() is the 33-byte compressed key — x-only pubkeys must go through .x_only_public_key().0 (one real bug the vectors caught). JNI glue adds com.archipelago.app.NativeCore: backupEncrypt/Decrypt, nostrGenerateSecret/SecretFromAny/ParseConnectUri/SignEvent and the NIP-44/NIP-04 cipher pairs. Android arm64 build verified via cargo-ndk (7.2 MB .so, +0.4 MB for both modules). Host: cargo test 23/23, clippy clean.
2026-08-31 13:29:36 +01:00
parent 12c853da45
commit 57e31eb192
6 changed files with 1621 additions and 3 deletions
@@ -0,0 +1,246 @@
+//! Companion app backup — the ADR-005 encrypted-backup envelope.
+//!
+//! Reuses the node's backup format exactly (ADR-005:
+//! `core/archipelago/src/backup/identity.rs`): Argon2id key derivation with
+//! default params, ChaCha20-Poly1305 AEAD, and the same blob layout
+//! `base64(salt[16] || nonce[12] || ciphertext)`. A companion backup and a
+//! node backup share one crypto story — the payload differs (the companion
+//! serializes its servers, FIPS identity and signer key instead of a node
+//! key), the envelope does not.
+//!
+//! The envelope is JSON with `version`, `kind`, `encrypted`, `blob` and
+//! `timestamp`; [`decrypt`] ignores any extra fields, so node envelopes
+//! (which carry `did`/`pubkey`/`kid`) decrypt here too.
+
+use anyhow::{bail, Context, Result};
+use argon2::Argon2;
+use base64::engine::general_purpose::STANDARD as BASE64;
+use base64::Engine;
+use chacha20poly1305::aead::{Aead, KeyInit};
+use chacha20poly1305::{ChaCha20Poly1305, Key, Nonce};
+use serde_json::json;
+
+/// Envelope version. Bump only when the blob layout itself changes — and
+/// then only with a reader for the old layout (same policy as the node).
+const BACKUP_VERSION: u32 = 1;
+const SALT_LEN: usize = 16;
+const NONCE_LEN: usize = 12;
+const KEY_LEN: usize = 32;
+
+/// Encrypt a JSON payload into an ADR-005 envelope.
+///
+/// The passphrase never leaves this call; the envelope carries only the
+/// salt (Argon2id parameter), the AEAD nonce, and the ciphertext.
+pub fn encrypt(payload: &str, passphrase: &str) -> Result<String> {
+    if payload.is_empty() {
+        bail!("backup payload is empty");
+    }
+    if passphrase.is_empty() {
+        bail!("backup passphrase must not be empty");
+    }
+
+    let mut salt = [0u8; SALT_LEN];
+    let mut nonce = [0u8; NONCE_LEN];
+    // Same CSPRNG discipline as identity generation (getrandom, see mesh.rs):
+    // OS RNG, never thread-local or derived-from-content randomness for key
+    // material or nonces.
+    getrandom::getrandom(&mut salt).context("OS RNG")?;
+    getrandom::getrandom(&mut nonce).context("OS RNG")?;
+
+    let key = derive_key(passphrase, &salt)?;
+    let cipher = ChaCha20Poly1305::new(Key::from_slice(&key));
+    let ciphertext = cipher
+        .encrypt(Nonce::from_slice(&nonce), payload.as_bytes())
+        .map_err(|_| anyhow::anyhow!("encryption failed"))?;
+
+    let mut blob = Vec::with_capacity(SALT_LEN + NONCE_LEN + ciphertext.len());
+    blob.extend_from_slice(&salt);
+    blob.extend_from_slice(&nonce);
+    blob.extend_from_slice(&ciphertext);
+
+    Ok(json!({
+        "version": BACKUP_VERSION,
+        "kind": "companion",
+        "encrypted": true,
+        "blob": BASE64.encode(&blob),
+        "timestamp": chrono_like_now(),
+    })
+    .to_string())
+}
+
+/// Decrypt an ADR-005 envelope back into its JSON payload.
+///
+/// Accepts `version: 1` envelopes regardless of `kind` or extra fields —
+/// the node's identity backups use the same blob, and being able to decrypt
+/// one here is free interop (the caller decides what to do with it).
+pub fn decrypt(envelope: &str, passphrase: &str) -> Result<String> {
+    let obj: serde_json::Value =
+        serde_json::from_str(envelope).context("not a JSON backup envelope")?;
+
+    if obj.get("version").and_then(|v| v.as_u64()) != Some(BACKUP_VERSION as u64) {
+        bail!("unsupported backup version (expected {BACKUP_VERSION})");
+    }
+
+    let blob_b64 = obj
+        .get("blob")
+        .and_then(|v| v.as_str())
+        .context("missing 'blob' in backup envelope")?;
+    let blob = BASE64
+        .decode(blob_b64)
+        .context("invalid base64 in backup blob")?;
+    if blob.len() < SALT_LEN + NONCE_LEN {
+        bail!("backup blob too short");
+    }
+
+    let salt = &blob[..SALT_LEN];
+    let nonce = &blob[SALT_LEN..SALT_LEN + NONCE_LEN];
+    let ciphertext = &blob[SALT_LEN + NONCE_LEN..];
+
+    let key = derive_key(passphrase, salt)?;
+    let cipher = ChaCha20Poly1305::new(Key::from_slice(&key));
+    let plaintext = cipher
+        .decrypt(Nonce::from_slice(nonce), ciphertext)
+        .map_err(|_| anyhow::anyhow!("decryption failed — wrong passphrase or corrupted backup"))?;
+
+    String::from_utf8(plaintext).context("decrypted payload is not valid UTF-8")
+}
+
+fn derive_key(passphrase: &str, salt: &[u8]) -> Result<[u8; KEY_LEN]> {
+    let mut key = [0u8; KEY_LEN];
+    Argon2::default()
+        .hash_password_into(passphrase.as_bytes(), salt, &mut key)
+        .map_err(|e| anyhow::anyhow!("Argon2 key derivation failed: {e}"))?;
+    Ok(key)
+}
+
+/// RFC 3339 UTC timestamp without pulling chrono into the .so — the node's
+/// envelope field is informational (display), not part of the authenticated
+/// or derived material.
+fn chrono_like_now() -> String {
+    let secs = std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .map(|d| d.as_secs())
+        .unwrap_or(0);
+    let days = secs / 86_400;
+    let rem = secs % 86_400;
+    let (h, m, s) = (rem / 3600, (rem % 3600) / 60, rem % 60);
+    // Civil-from-days (Howard Hinnant's algorithm), valid for 1970-2100+.
+    let z = days as i64 + 719_468;
+    let era = z.div_euclid(146_097);
+    let doe = z.rem_euclid(146_097);
+    let yoe = (doe - doe / 1460 + doe / 36_524 - doe / 146_096) / 365;
+    let y = yoe + era * 400;
+    let doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
+    let mp = (5 * doy + 2) / 153;
+    let d = doy - (153 * mp + 2) / 5 + 1;
+    let mo = if mp < 10 { mp + 3 } else { mp - 9 };
+    let y = if mo <= 2 { y + 1 } else { y };
+    format!("{y:04}-{mo:02}-{d:02}T{h:02}:{m:02}:{s:02}Z")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const PAYLOAD: &str = r#"{"app":"archipelago-companion","servers":["192.168.1.10|false|1301||Lab Node|fd00::1|npub1abc"]}"#;
+
+    #[test]
+    fn round_trip() {
+        let envelope = encrypt(PAYLOAD, "correct horse battery staple").unwrap();
+        let decrypted = decrypt(&envelope, "correct horse battery staple").unwrap();
+        assert_eq!(decrypted, PAYLOAD);
+    }
+
+    #[test]
+    fn wrong_passphrase_fails() {
+        let envelope = encrypt(PAYLOAD, "right").unwrap();
+        let err = decrypt(&envelope, "wrong").unwrap_err();
+        assert!(
+            err.to_string().contains("wrong passphrase"),
+            "error should name the likely cause: {err}"
+        );
+    }
+
+    #[test]
+    fn envelope_shape_matches_node_format() {
+        let envelope = encrypt(PAYLOAD, "pw").unwrap();
+        let obj: serde_json::Value = serde_json::from_str(&envelope).unwrap();
+
+        assert_eq!(obj["version"], 1);
+        assert_eq!(obj["encrypted"], true);
+        assert!(obj["kind"].as_str().is_some());
+        assert!(obj["timestamp"].as_str().is_some());
+
+        // Blob layout is exactly the node's: base64(salt||nonce||ct) with the
+        // AEAD tag inside the ciphertext — at least 16+12+16+1 bytes.
+        let blob = BASE64
+            .decode(obj["blob"].as_str().unwrap())
+            .expect("blob is base64");
+        assert!(blob.len() >= SALT_LEN + NONCE_LEN + 16 + PAYLOAD.len());
+    }
+
+    #[test]
+    fn fresh_salt_and_nonce_every_time() {
+        let a = encrypt(PAYLOAD, "pw").unwrap();
+        let b = encrypt(PAYLOAD, "pw").unwrap();
+        let (oa, ob): (serde_json::Value, serde_json::Value) = (
+            serde_json::from_str(&a).unwrap(),
+            serde_json::from_str(&b).unwrap(),
+        );
+        assert_ne!(oa["blob"], ob["blob"], "salt/nonce must never repeat");
+    }
+
+    #[test]
+    fn tampered_blob_fails_to_decrypt() {
+        let envelope = encrypt(PAYLOAD, "pw").unwrap();
+        let mut obj: serde_json::Value = serde_json::from_str(&envelope).unwrap();
+        let blob = BASE64.decode(obj["blob"].as_str().unwrap()).unwrap();
+        let mut tampered = blob.clone();
+        // Flip a bit inside the ciphertext (past salt+nonce).
+        tampered[SALT_LEN + NONCE_LEN] ^= 0x01;
+        obj["blob"] = serde_json::Value::String(BASE64.encode(&tampered));
+        assert!(decrypt(&obj.to_string(), "pw").is_err());
+    }
+
+    /// Node identity backups use the same blob layout but carry their own
+    /// envelope fields (did/pubkey/kid). Decrypt must ignore those extras —
+    /// one envelope reader, two producers.
+    #[test]
+    fn node_style_envelope_with_extra_fields_decrypts() {
+        let envelope = encrypt(PAYLOAD, "pw").unwrap();
+        let mut obj: serde_json::Value = serde_json::from_str(&envelope).unwrap();
+        obj["kind"] = serde_json::Value::String("node-identity".into());
+        obj["did"] = serde_json::Value::String("did:key:z6Mktest".into());
+        obj["pubkey"] = serde_json::Value::String("aabbcc".into());
+        obj["kid"] = serde_json::Value::String("did:key:z6Mktest#key-1".into());
+        let decrypted = decrypt(&obj.to_string(), "pw").unwrap();
+        assert_eq!(decrypted, PAYLOAD);
+    }
+
+    #[test]
+    fn rejects_unknown_version_and_garbage() {
+        let err = decrypt("{\"version\":99,\"blob\":\"AAAA\"}", "pw").unwrap_err();
+        assert!(err.to_string().contains("version"));
+        assert!(decrypt("not json", "pw").is_err());
+        assert!(decrypt("{\"version\":1}", "pw").is_err());
+    }
+
+    #[test]
+    fn rejects_empty_passphrase_and_payload() {
+        assert!(encrypt(PAYLOAD, "").is_err());
+        assert!(encrypt("", "pw").is_err());
+    }
+
+    #[test]
+    fn timestamp_is_rfc3339_utc() {
+        let envelope = encrypt(PAYLOAD, "pw").unwrap();
+        let obj: serde_json::Value = serde_json::from_str(&envelope).unwrap();
+        let ts = obj["timestamp"].as_str().unwrap();
+        // 2026-08-31T12:34:56Z — 20 chars, RFC 3339 UTC.
+        assert_eq!(ts.len(), 20);
+        assert!(ts.ends_with('Z'));
+        assert_eq!(&ts[4..5], "-");
+        assert_eq!(&ts[10..11], "T");
+        assert!(ts.starts_with("20"));
+    }
+}