# metamorphic-crypto
Zero-knowledge end-to-end encryption library with post-quantum hybrid KEM, hybrid
PQ signatures, and an opt-in **CNSA 2.0** suite axis (matched-strength hybrid +
pure ML-KEM-1024 / ML-DSA-87 / AES-256-GCM).
Built for [Metamorphic](https://metamorphic.app) and [Mosslet](https://mosslet.com) — privacy-first apps by [Moss Piglet Corporation](https://mosspiglet.dev) where all user data is encrypted client-side and the server only stores opaque ciphertext.
## What this provides
- **Secretbox** (XSalsa20-Poly1305) — symmetric authenticated encryption
- **Sealed box** (X25519) — anonymous public-key encryption (libsodium-compatible)
- **Hybrid PQ KEM** (ML-KEM-512 + X25519) — NIST Cat-1 post-quantum key encapsulation (opt-in)
- **Hybrid PQ KEM** (ML-KEM-768 + X25519) — NIST Cat-3 post-quantum key encapsulation (default)
- **Hybrid PQ KEM** (ML-KEM-1024 + X25519) — NIST Cat-5 post-quantum key encapsulation (opt-in)
- **Argon2id KDF** — password-based key derivation (libsodium INTERACTIVE parameters)
- **Hybrid PQ signatures** (ML-DSA + Ed25519) — NIST Cat-2/3/5 composite digital signatures (strict AND)
- **CNSA 2.0 suite axis** (opt-in) — matched-strength hybrid (X448 / P-521 / Ed448 / ECDSA-P-521) and pure post-quantum (ML-KEM-1024, ML-DSA-87, AES-256-GCM)
- **Hashing** (SHA3-512/256, SHA-256/512) — public, one-shot digest functions (e.g. for key fingerprints / safety numbers)
- **Verifiable random function** (ECVRF-EDWARDS25519-SHA512-TAI, RFC 9381) — classical VRF for transparency-log *index privacy* (CONIKS-style)
- **WASM bindings** — browser-ready via `wasm-pack`
- **Recovery keys** — human-readable base32 encoding for key backup
## Security levels
| Level | ML-KEM | NIST Category | Equivalent | Version Tag | Default |
|-------|--------|---------------|------------|-------------|---------|
| Cat-1 | 512 | 1 | ~AES-128 | `0x01` | No |
| Cat-3 | 768 | 3 | ~AES-192 | `0x02` | Yes |
| Cat-5 | 1024 | 5 | ~AES-256 | `0x03` | No |
NIST (FIPS 203) standardizes ML-KEM only at categories 1/3/5 — there is no category-2/4 parameter set, so none is offered. All levels use the same combiner construction. The classical half is **X25519 (~Cat-1 classical) at every tier** — it does not scale up with the ML-KEM parameter set; at Cat-3/Cat-5 the post-quantum half dominates and X25519 is the classical floor (standard hybrid-KEM practice: a break requires defeating *both* halves). `hybrid_open` auto-detects the level from the version tag byte — old and new ciphertext coexist seamlessly.
## Security properties
- `#![forbid(unsafe_code)]` — no unsafe anywhere in the crate
- All secret key material zeroized after use
- Constant-time MAC comparison via RustCrypto
- OS CSPRNG via `getrandom` (no userspace PRNG)
- Hybrid construction: both ML-KEM AND X25519 must be broken to compromise a sealed key
## Hybrid KEM construction
The hybrid combiner matches the format used by [`@noble/post-quantum`](https://github.com/paulmillr/noble-post-quantum)'s `ml_kem768_x25519`:
```
Seed expansion: SHAKE256(seed_32) → 96 bytes [ML-KEM seed (64) || X25519 sk (32)]
Combiner: SHA3-256(ss_mlkem || ss_x25519 || ct_x25519 || pk_x25519 || label)
```
### Cat-1 (ML-KEM-512, opt-in)
```
Public key: ML-KEM-512 ek (800 B) || X25519 pk (32 B) = 832 bytes
Ciphertext: 0x01 || ML-KEM-512 ct (768 B) || X25519 eph pk (32 B) || nonce (24 B) || secretbox ct
```
### Cat-3 (ML-KEM-768, default)
```
Public key: ML-KEM-768 ek (1184 B) || X25519 pk (32 B) = 1216 bytes
Ciphertext: 0x02 || ML-KEM-768 ct (1088 B) || X25519 eph pk (32 B) || nonce (24 B) || secretbox ct
```
### Cat-5 (ML-KEM-1024, opt-in)
```
Public key: ML-KEM-1024 ek (1568 B) || X25519 pk (32 B) = 1600 bytes
Ciphertext: 0x03 || ML-KEM-1024 ct (1568 B) || X25519 eph pk (32 B) || nonce (24 B) || secretbox ct
```
## Targets
| Target | Build | Use case |
|--------|-------|----------|
| Native | `cargo build` | Tests, CLI tools, Elixir NIF (`metamorphic_crypto` Hex package) |
| WASM | `wasm-pack build --target web` | Browser (Phoenix LiveView, any SPA) |
| iOS | UniFFI (planned) | Native Swift apps |
| Android | UniFFI (planned) | Native Kotlin apps |
## Usage
```rust
use metamorphic_crypto::{generate_key, encrypt_secretbox_string, decrypt_secretbox_to_string};
use metamorphic_crypto::{generate_hybrid_keypair, hybrid_seal, hybrid_open};
use metamorphic_crypto::{generate_hybrid_keypair_512, hybrid_seal_512};
use metamorphic_crypto::{generate_hybrid_keypair_1024, hybrid_seal_1024};
// Symmetric encryption
let key = generate_key();
let ciphertext = encrypt_secretbox_string("sensitive data", &key).unwrap();
let plaintext = decrypt_secretbox_to_string(&ciphertext, &key).unwrap();
assert_eq!(plaintext, "sensitive data");
// Hybrid PQ seal (Cat-3, default)
let kp = generate_hybrid_keypair();
let sealed = hybrid_seal(b"context_key_bytes", &kp.public_key).unwrap();
let opened = hybrid_open(&sealed, &kp.secret_key).unwrap();
// Hybrid PQ seal (Cat-5)
let kp5 = generate_hybrid_keypair_1024();
let sealed5 = hybrid_seal_1024(b"context_key_bytes", &kp5.public_key).unwrap();
let opened5 = hybrid_open(&sealed5, &kp5.secret_key).unwrap(); // auto-detects level
// Hybrid PQ seal (Cat-1)
let kp1 = generate_hybrid_keypair_512();
let sealed1 = hybrid_seal_512(b"context_key_bytes", &kp1.public_key).unwrap();
let opened1 = hybrid_open(&sealed1, &kp1.secret_key).unwrap(); // auto-detects level
```
## Hashing
Public, one-shot digest functions over the already-present, audited `sha3` and
`sha2` dependencies. These are intended for **public** data only — key
fingerprints / safety numbers and key-transparency-log entries — where both the
input (e.g. a public key) and the output digest are meant to be public.
`sha3_512` is the recommended default (NIST Cat-5, ~256-bit collision
resistance, consistent with the crate's Keccak-based combiner). `sha3_256`,
`sha256`, and `sha512` are provided so integrators can match an existing format.
```rust
use metamorphic_crypto::{sha3_512, sha3_256, sha256, sha512};
// Take raw bytes, return fixed-size byte arrays.
let digest: [u8; 64] = sha3_512(b"public key bytes"); // recommended default
let d256: [u8; 32] = sha3_256(b"...");
let s256: [u8; 32] = sha256(b"..."); // SHA-2 interop
let s512: [u8; 64] = sha512(b"..."); // SHA-2 interop
// Encode the digest yourself when needed:
use metamorphic_crypto::b64;
let fingerprint_b64 = b64::encode(&digest);
```
### Domain separation (recommended for fingerprints / transparency logs)
For key fingerprints, safety numbers, and key-transparency-log entries, prefer
`sha3_512_with_context`, which binds the digest to a versioned context label so
the same bytes hashed for different purposes can never collide or be
reinterpreted across contexts. It is exactly as strong as `sha3_512` — it *is*
SHA3-512, over an unambiguously framed message — and makes intent explicit:
```rust
use metamorphic_crypto::sha3_512_with_context;
let fp = sha3_512_with_context("mosslet/key-fingerprint/v1", pubkey_bytes);
let log = sha3_512_with_context("mosslet/log-entry/v1", entry_bytes);
// fp and log are unrelated even if the byte inputs coincide.
```
Stable wire format (reproduce exactly for cross-language parity):
```text
SHA3-512( u64_be(len(context_utf8)) || context_utf8 || data )
```
The 8-byte big-endian length prefix makes the `(context, data)` boundary
unambiguous (no boundary-confusion collisions). Use a versioned namespace label.
Encoding: the native functions take `&[u8]` and return raw byte arrays — encode
to base64 or hex at the call site. The WASM bindings take/return base64 to match
the rest of the WASM API (see below).
**Do not hash secrets with these.** A bare hash makes no guarantees about its
inputs, and (consistent with the rest of the crate) the hashing path adds no
zeroize/constant-time ceremony — wiping a transient copy of already-public data
would add cost without protection. If you need to process secret material
(passwords, private keys), use the right construction instead — this crate's
Argon2id `derive_session_key` for password-based derivation, or a dedicated
KDF/MAC. The encryption APIs that handle secrets already zeroize on drop.
## Verifiable random function (ECVRF, RFC 9381)
The `vrf` module exposes **ECVRF-EDWARDS25519-SHA512-TAI** — RFC 9381 ciphersuite
`0x03`: Edwards25519 + SHA-512 + the try-and-increment hash-to-curve. A VRF lets
the key owner compute, for any input `alpha`, a pseudorandom output `beta` plus a
proof `pi` that `beta` is correct under their public key. Anyone with the public
key can verify `pi`, but cannot compute `beta` for a new input and cannot learn
`alpha` from `(pi, beta)`. This is the primitive behind **transparency-log index
privacy** (CONIKS-style): a directory maps a private identity index to a
verifiable, pseudorandom tree position without revealing which identities it
holds.
It is built on the **same `curve25519-dalek` backend** as the Ed25519 interop
module — no new curve stack — and is pinned byte-for-byte by RFC 9381's own test
vectors.
```rust
use metamorphic_crypto::{ecvrf_generate_keypair, ecvrf_prove, ecvrf_verify};
let (sk, pk) = ecvrf_generate_keypair();
let alpha = b"identity index";
let pi = ecvrf_prove(&sk, alpha)?; // 80-byte proof
let beta = ecvrf_verify(&pk, alpha, &pi)?; // Ok(Some(beta)) if valid
assert!(beta.is_some());
```
| Item | Bytes | Layout |
|------|-------|--------|
| secret key | 32 | Ed25519-style seed |
| public key | 32 | compressed Edwards `Y = x*B` |
| proof `pi` | 80 | `Gamma(32) \|\| c(16) \|\| s(32)` |
| output `beta` | 64 | `SHA-512(0x03 \|\| 0x03 \|\| cofactor*Gamma \|\| 0x00)` |
**Honest posture.** This VRF is **classical** (elliptic-curve discrete log). It
protects exactly one property — *index privacy* — and is the one non-post-quantum
piece in the transparency stack; integrity, authenticity, confidentiality, and
hash-based commitments are post-quantum independently of it. RFC 9381's sibling
`ECVRF-EDWARDS25519-SHA512-ELL2` (`0x04`, constant-time Elligator2 hash-to-curve)
is a designed-in future addition that lands when the released curve backend
exposes a conformant hash-to-curve (curve25519-dalek 5.x); because the suite
octet is bound into every hash, adding it is purely additive and never
invalidates a `0x03` proof. A hybrid (post-quantum + classical) VRF is intended
for when an audited lattice VRF exists; none does today, so it is not built.
These primitives are not FIPS-validated.
## Hybrid PQ signatures
Composite digital signatures: every message is signed by **both** ML-DSA
(FIPS 204) **and** Ed25519 (RFC 8032), and verification requires **both** to be
valid (strict AND). An attacker has to break both a lattice scheme and an
elliptic-curve scheme to forge, and cannot strip one algorithm to downgrade the
other. This is the signing counterpart to the hybrid KEM above.
```rust
use metamorphic_crypto::{generate_signing_keypair, sign, verify, SIGN_CONTEXT_V1};
let kp = generate_signing_keypair(); // Cat-3 (ML-DSA-65 + Ed25519), default
let sig = sign(b"transparency log entry", SIGN_CONTEXT_V1, &kp.secret_key).unwrap();
assert!(verify(b"transparency log entry", SIGN_CONTEXT_V1, &sig, &kp.public_key).unwrap());
// Re-derive the public key from a backed-up secret key:
use metamorphic_crypto::derive_public_key;
assert_eq!(derive_public_key(&kp.secret_key).unwrap(), kp.public_key);
```
Cat-2 (`generate_signing_keypair_44`) and Cat-5 (`generate_signing_keypair_87`)
are also available; `verify` auto-detects the level from the signature's version
tag. The `secret_key` field is zeroized on drop.
### Signing levels and mode
| Level | ML-DSA | NIST Category | Equivalent | Version Tag | Default |
|-------|-----------|---------------|------------|-------------|---------|
| Cat-2 | ML-DSA-44 | 2 | ~AES-128 | `0x01` | No |
| Cat-3 | ML-DSA-65 | 3 | ~AES-192 | `0x02` | Yes |
| Cat-5 | ML-DSA-87 | 5 | ~AES-256 | `0x03` | No |
ML-DSA is signed with the **hedged (randomized)** variant — FIPS 204's default
and most conservative mode (resilient to RNG failure, hardened against fault /
side-channel attacks that deterministic lattice signing invites). Ed25519 is
deterministic per RFC 8032. As a result signature **bytes are non-reproducible**,
but the **wire format is deterministic and pinned**.
### Domain separation and wire format
Both algorithms sign the same domain-separated message, framed exactly like
`sha3_512_with_context` (a length-prefixed context):
```text
signed_msg = I2OSP(len(context_utf8), 8) || context_utf8 || message
```
ML-DSA signs `signed_msg` with an empty native context, so the framing is
identical for both algorithms and across every language binding. Byte layout
(Ed25519 first, fixed-size, so the ML-DSA tail needs no length prefix):
```text
signature = tag || ed25519_sig (64 B) || ml_dsa_sig (2420 / 3309 / 4627 B)
public_key = tag || ed25519_pk (32 B) || ml_dsa_pk (1312 / 1952 / 2592 B)
secret_key = tag || ed25519_seed(32 B) || ml_dsa_seed(32 B) = 65 B
```
### Dependency audit posture
| Dependency | Version | Audited | Notes |
|-----------------|---------|---------------------|-------|
| `ed25519-dalek` | 2.x | Yes (mature) | Widely deployed RFC 8032 implementation. |
| `ml-dsa` | 0.1.x | **No** (RustCrypto) | FIPS 204 (final). New crate, not yet independently audited. Pinned; tracked for the FIPS-mode roadmap. |
ML-DSA is defense-in-depth on top of the independently-strong Ed25519: even if a
flaw were found in the young `ml-dsa` implementation, the composite remains at
least as strong as Ed25519. This is stated honestly so integrators can choose
while the post-quantum implementation matures toward audit / FIPS validation.
## CNSA 2.0 suite axis (opt-in)
By default everything above is **`Suite::Hybrid`** — the classical+PQ strict-AND
constructions (ML-KEM + X25519; ML-DSA + Ed25519). If you have no specific
mandate, that is the recommended choice and you can ignore this section.
For deployments that must follow the NSA's **Commercial National Security
Algorithm Suite 2.0** (CNSA 2.0 / NIST IR 8547), a `Suite` axis lets you raise
the posture with a *single extra argument*. It is **orthogonal** to the
`SecurityLevel` (Cat-1/3/5) you already know, so you really have two independent
knobs:
```
posture (Suite) × parameter set (SecurityLevel)
┌──────────────────────────────┐ ┌───────────────────────┐
│ Hybrid (default) │ │ Cat-1 / Cat-3 / Cat-5 │
│ HybridMatched (opt-in) │ └───────────────────────┘
│ PureCnsa2 (opt-in) │
└──────────────────────────────┘
```
| Suite | What it is | Classical partner | Status |
|-------|------------|-------------------|--------|
| `Hybrid` | Existing strict-AND classical+PQ. **Byte-for-byte unchanged.** | X25519 / Ed25519 (every tier) | **Default, recommended** |
| `HybridMatched` | Classical partner matched to the PQ category so it is never the weak link | KEM: Cat-3→X448, Cat-5→P-521 ECDH · Sign: Cat-3→Ed448, Cat-5→ECDSA-P-521 | Opt-in |
| `PureCnsa2` | Pure post-quantum, no classical half (the CNSA-2.0 box) | none | Opt-in, **Cat-5 only** |
`HybridMatched` at the lowest rung (KEM Cat-1 / sign Cat-2) is identical to
`Hybrid` — no new format is produced there, so nothing breaks.
### New wire formats (new suites only)
The `Hybrid` suite (and `HybridMatched` at the lowest rung) keep their existing
`0x01/0x02/0x03` ciphertext tags and byte layout untouched. The matched / pure
suites use new tags and a CNSA-correct seal envelope:
| Suite + level | KEM | Tag |
|---------------|-----|-----|
| `PureCnsa2` Cat-5 | ML-KEM-1024 + AES-256-GCM | `0x10` |
| `HybridMatched` Cat-3 | ML-KEM-768 + X448 + AES-256-GCM | `0x13` |
| `HybridMatched` Cat-5 | ML-KEM-1024 + P-521 ECDH + AES-256-GCM | `0x14` |
```text
ikm = ss_mlkem (PureCnsa2) | ss_mlkem || ss_ecc (HybridMatched)
key = HKDF-SHA512(ikm, info = suite_tag || context_label) -> 32-byte AES-256 key
out = AES-256-GCM(key, 96-bit random nonce, AAD = suite_tag || context_label)
wire = tag(1) || kem_ct || [ecc_eph_pk] || nonce(12) || ct || gcm_tag(16)
```
Each encapsulation yields a fresh KEM secret, so the derived AES-256 key is
single-use and the random 96-bit nonce can never repeat — SIV-grade misuse
resistance without leaving the CNSA-approved set (no AES-GCM-SIV). Note the
deliberate hash split: **HKDF-SHA512** for *key derivation* here; **SHA3-512**
stays the choice for *leaf/transcript* hashing (`sha3_512_with_context`).
### Context labels
The new suites bind a versioned context label into both the HKDF `info` and the
GCM AAD (and, for signatures, the I2OSP-framed message). Grammar:
`"<namespace>/<purpose>/v<major>"`. The **namespace** is the one per-tenant knob;
the protocol shape stays fixed. Library defaults are `SEAL_CONTEXT_V1`
(`"metamorphic/seal/v1"`) and `SIGN_CONTEXT_V1` (`"metamorphic/sign/v1"`); pass
your own (e.g. `"mosslet/seal/v1"`) to namespace your deployment.
### Usage (Rust)
```rust
use metamorphic_crypto::{
Suite, SecurityLevel, SignatureLevel, SEAL_CONTEXT_V1, SIGN_CONTEXT_V1,
generate_hybrid_keypair_suite, hybrid_seal_suite, hybrid_open_with_context,
generate_signing_keypair_suite, sign, verify,
};
// --- KEM / seal: the pure CNSA-2.0 box (ML-KEM-1024 + AES-256-GCM) ---
let kp = generate_hybrid_keypair_suite(Suite::PureCnsa2, SecurityLevel::Cat5).unwrap();
let sealed = hybrid_seal_suite(b"context_key_bytes", &kp.public_key,
Suite::PureCnsa2, SecurityLevel::Cat5).unwrap();
// `hybrid_open` auto-detects the tag using the DEFAULT context label; if you
// sealed with a custom label, open with it explicitly:
let opened = hybrid_open_with_context(&sealed, &kp.secret_key, SEAL_CONTEXT_V1).unwrap();
// --- Signatures: ML-DSA-87 only (Cat-5 pure) ---
let sk = generate_signing_keypair_suite(Suite::PureCnsa2, SignatureLevel::Cat5).unwrap();
let sig = sign(b"checkpoint", SIGN_CONTEXT_V1, &sk.secret_key).unwrap();
assert!(verify(b"checkpoint", SIGN_CONTEXT_V1, &sig, &sk.public_key).unwrap());
// `sign` / `verify` / `derive_public_key` auto-detect the suite from the version
// tag — no suite argument is needed once the key exists.
```
`seal_for_user_with_suite` is the user-facing seal that falls back to legacy
X25519 when no PQ key is present, mirroring `seal_for_user_with_level`.
### Honest claims
Claim: **"CNSA 2.0 algorithm suite, NCC-audited components, pure-Rust,
memory-safe (`forbid-unsafe`)."** **Not** "FIPS 140-3 validated." `PureCnsa2` is
more standards-compliant but leans entirely on the (not-yet-independently-audited
at our layer) lattice implementation, which is exactly why the strict-AND
`Hybrid` default stays recommended: it keeps the classical backstop until the PQ
implementations are audited / validated.
## WASM (browser)
```bash
wasm-pack build --target web --release
```
```js
import init, { deriveSessionKey, encryptSecretboxString } from './pkg/metamorphic_crypto.js';
await init('/path/to/metamorphic_crypto_bg.wasm');
const key = deriveSessionKey(password, saltBase64);
const ciphertext = encryptSecretboxString("hello", key);
```
### Hashing (WASM)
Digest exports take base64-encoded input and return the digest as base64. Decode
or re-encode to hex on the JS side if a hex fingerprint is required.
```js
import init, { sha3_512, sha3_512WithContext } from './pkg/metamorphic_crypto.js';
await init();
const dataB64 = btoa("public key bytes");
const digestB64 = sha3_512(dataB64); // also: sha3_256, sha256, sha512
// Domain-separated (recommended for fingerprints / transparency logs):
const fp = sha3_512WithContext("mosslet/key-fingerprint/v1", dataB64);
```
### Signatures (WASM)
Keys and signatures are base64; the message is base64 and `context` is a UTF-8
string. `verify` returns `true` only if both component signatures are valid.
```js
import init, { generateSigningKeyPair, sign, verify } from './pkg/metamorphic_crypto.js';
await init();
const kp = generateSigningKeyPair("cat3"); // { publicKey, secretKey }
const msg = btoa("transparency log entry");
const sig = sign(msg, "metamorphic/sign/v1", kp.secretKey);
const ok = verify(msg, "metamorphic/sign/v1", sig, kp.publicKey); // true
```
### CNSA 2.0 suites (WASM)
The `Suite` axis is exposed as a string argument (`"hybrid"` (default),
`"hybridMatched"`, or `"pureCnsa2"`) alongside the usual `"cat1"`/`"cat3"`/`"cat5"`
level. Decryption / verification auto-detect the suite from the version tag.
```js
import init, {
generateHybridKeyPairSuite, hybridSealSuite, hybridOpenWithContext,
generateSigningKeyPairSuite, sign, verify,
} from './pkg/metamorphic_crypto.js';
await init();
// Pure CNSA-2.0 KEM box (ML-KEM-1024 + AES-256-GCM)
const kp = generateHybridKeyPairSuite("pureCnsa2", "cat5"); // { publicKey, secretKey }
const sealed = hybridSealSuite(btoa("key material"), kp.publicKey, "pureCnsa2", "cat5");
// Open with the context label used at seal time (default "metamorphic/seal/v1"):
const opened = hybridOpenWithContext(sealed, kp.secretKey, "metamorphic/seal/v1"); // base64
// Pure ML-DSA-87 signatures
const sk = generateSigningKeyPairSuite("pureCnsa2", "cat5");
const sig = sign(btoa("checkpoint"), "metamorphic/sign/v1", sk.secretKey);
const ok = verify(btoa("checkpoint"), "metamorphic/sign/v1", sig, sk.publicKey); // true
```
For a custom per-tenant namespace, use `hybridSealSuiteWithContext(...,
"mosslet/seal/v1")` and open with the same label. `sealForUserWithSuite` mirrors
`sealForUser` with the suite/level appended.
## Tests
```bash
cargo test # unit + integration + cross-level compatibility
cargo clippy # zero warnings
cargo fmt --check # formatted
```
## License
Dual-licensed under [MIT](LICENSE-MIT) or [Apache-2.0](LICENSE-APACHE) at your option.