# BLS12-381 Aggregate Signatures in Rust using Apache Milagro

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**WARNING: This library is a work in progress and has not been audited. Do NOT consider the cryptography safe!**

Uses the [The Apache Milagro Cryptographic Library](https://github.com/apache/incubator-milagro-crypto-rust).

This crate is heavily based upon work by
[@lovesh](https://github.com/lovesh).

Presently this library only supports features required for Ethereum 2.0
signature validation. The aggregation methods here are vulnerable to the
rouge-key attack.

There has been no public audit or scrutiny placed upon this crate. If you're a
cryptographer I would love to have your input.

This library uses a Proof of Possession (PoP) variant as protection against rogue key attacks.
A public key can be PoP verified by signing a hash of the public key. This must be done
before a `PublicKey` may be used in any aggregate signatures.

Subgroup checks are performed for signatures during verification and public keys
during deserialisation.

## BLS Standard

Current implementation of the BLS Standard aligns with [bls-signatures-v04](https://tools.ietf.org/html/draft-irtf-cfrg-bls-signature-04)
and [hash-to-curve-v09](https://tools.ietf.org/html/draft-irtf-cfrg-hash-to-curve-09).

## Usage

### Single Signatures

Perform signing and verification of non-aggregate BLS signatures. Supports
serializing and de-serializing both public and secret keys.

```rust
let sk_bytes = vec![
	78, 252, 122, 126, 32, 0, 75, 89, 252, 31, 42, 130, 254, 88, 6, 90, 138, 202, 135, 194,
	233, 117, 181, 75, 96, 238, 79, 100, 237, 59, 140, 111,
];

// Load some keys from a serialized secret key.
let sk = SecretKey::from_bytes(&sk_bytes).unwrap();
let pk = PublicKey::from_secret_key(&sk);

// Sign a message
let message = "cats".as_bytes();
let signature = Signature::new(&message, &sk);
assert!(signature.verify(&message, &pk));

// Serialize then de-serialize, just 'cause we can.
let pk_bytes = pk.as_bytes();
let pk = PublicKey::from_bytes(&pk_bytes).unwrap();

// Verify the message
assert!(signature.verify(&message, &pk));
```

Generate new "random" secret keys (see `SecretKey` docs for information on
entropy sources).

```rust
// Generate a random key pair.
let sk = SecretKey::random(&mut rand::thread_rng());
let pk = PublicKey::from_secret_key(&sk);

// Sign and verify a message.
let message = "cats".as_bytes();
let signature = Signature::new(&message, &sk);
assert!(signature.verify(&message, &pk));
```

### Aggregate Signatures

Aggregate signatures and public keys. Supports serializing and de-serializing
both `AggregateSignatures` and `AggregatePublicKeys`.

```rust
let signing_secret_key_bytes = vec![
		vec![
				98, 161, 50, 32, 254, 87, 16, 25, 167, 79, 192, 116, 176, 74, 164, 217, 40, 57,
				179, 15, 19, 21, 240, 100, 70, 127, 111, 170, 129, 137, 42, 53,
		],
		vec![
				53, 72, 211, 104, 184, 68, 142, 208, 115, 22, 156, 97, 28, 216, 228, 102, 4, 218,
				116, 226, 166, 131, 67, 7, 40, 55, 157, 167, 157, 127, 143, 13,
		],
];

// Load the key pairs from our serialized secret keys,
let signing_keypairs: Vec<Keypair> = signing_secret_key_bytes
		.iter()
		.map(|bytes| {
				let sk = SecretKey::from_bytes(&bytes).unwrap();
				let pk = PublicKey::from_secret_key(&sk);
				Keypair { sk, pk }
		})
		.collect();

let message = "cats".as_bytes();

// Create an aggregate signature over some message, also generating an
// aggregate public key at the same time.
let mut agg_sig = AggregateSignature::new();
let mut public_keys = vec![];
for keypair in &signing_keypairs {
		let sig = Signature::new(&message, &keypair.sk);
		agg_sig.add(&sig);
		public_keys.push(keypair.pk.clone());
}
let agg_pub_key = AggregatePublicKey::into_aggregate(&public_keys).unwrap();

// Serialize and de-serialize the aggregates, just 'cause we can.
let agg_sig_bytes = agg_sig.as_bytes();
let agg_sig = AggregateSignature::from_bytes(&agg_sig_bytes).unwrap();

// Verify the AggregateSignature against the AggregatePublicKey
assert!(agg_sig.fast_aggregate_verify_pre_aggregated(&message, &agg_pub_key));
}
```

### How to Run Benchmarks

```
cargo bench --features "bench"
```