Encryption support for the statement store (#14440)

* Added ECIES encryption

* tweaks

* fmt

* Make clippy happy

* Use local keystore

* qed

substrate/primitives/statement-store/src/ecies.rs

@@ -0,0 +1,174 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// tag::description[]
+//! ECIES encryption scheme using x25519 key exchange and AEAD.
+// end::description[]
+
+use aes_gcm::{aead::Aead, AeadCore, KeyInit};
+use rand::rngs::OsRng;
+use sha2::Digest;
+use sp_core::crypto::Pair;
+
+/// x25519 secret key.
+pub type SecretKey = x25519_dalek::StaticSecret;
+/// x25519 public key.
+pub type PublicKey = x25519_dalek::PublicKey;
+
+/// Encryption or decryption error.
+#[derive(Debug, PartialEq, Eq, thiserror::Error)]
+pub enum Error {
+	/// Generic AES encryption error.
+	#[error("Encryption error")]
+	Encryption,
+	/// Generic AES decryption error.
+	#[error("Decryption error")]
+	Decryption,
+	/// Error reading key data. Not enough data in the buffer.
+	#[error("Bad cypher text")]
+	BadData,
+}
+
+const NONCE_LEN: usize = 12;
+const PK_LEN: usize = 32;
+const AES_KEY_LEN: usize = 32;
+
+fn aes_encrypt(key: &[u8; AES_KEY_LEN], nonce: &[u8], plaintext: &[u8]) -> Result<Vec<u8>, Error> {
+	let enc = aes_gcm::Aes256Gcm::new(key.into());
+
+	enc.encrypt(nonce.into(), aes_gcm::aead::Payload { msg: plaintext, aad: b"" })
+		.map_err(|_| Error::Encryption)
+}
+
+fn aes_decrypt(key: &[u8; AES_KEY_LEN], nonce: &[u8], ciphertext: &[u8]) -> Result<Vec<u8>, Error> {
+	let dec = aes_gcm::Aes256Gcm::new(key.into());
+	dec.decrypt(nonce.into(), aes_gcm::aead::Payload { msg: ciphertext, aad: b"" })
+		.map_err(|_| Error::Decryption)
+}
+
+fn kdf(shared_secret: &[u8]) -> [u8; AES_KEY_LEN] {
+	let hkdf = hkdf::Hkdf::<sha2::Sha256>::new(None, shared_secret);
+	let mut aes_key = [0u8; AES_KEY_LEN];
+	hkdf.expand(b"", &mut aes_key)
+		.expect("There's always enough data for derivation. qed.");
+	aes_key
+}
+
+/// Encrypt `plaintext` with the given public x25519 public key. Decryption can be performed with
+/// the matching secret key.
+pub fn encrypt_x25519(pk: &PublicKey, plaintext: &[u8]) -> Result<Vec<u8>, Error> {
+	let ephemeral_sk = x25519_dalek::StaticSecret::new(OsRng);
+	let ephemeral_pk = x25519_dalek::PublicKey::from(&ephemeral_sk);
+
+	let mut shared_secret = ephemeral_sk.diffie_hellman(pk).to_bytes().to_vec();
+	shared_secret.extend_from_slice(ephemeral_pk.as_bytes());
+
+	let aes_key = kdf(&shared_secret);
+
+	let nonce = aes_gcm::Aes256Gcm::generate_nonce(OsRng);
+	let ciphertext = aes_encrypt(&aes_key, &nonce, plaintext)?;
+
+	let mut out = Vec::with_capacity(ciphertext.len() + PK_LEN + NONCE_LEN);
+	out.extend_from_slice(ephemeral_pk.as_bytes());
+	out.extend_from_slice(nonce.as_slice());
+	out.extend_from_slice(ciphertext.as_slice());
+
+	Ok(out)
+}
+
+/// Encrypt `plaintext` with the given ed25519 public key. Decryption can be performed with the
+/// matching secret key.
+pub fn encrypt_ed25519(pk: &sp_core::ed25519::Public, plaintext: &[u8]) -> Result<Vec<u8>, Error> {
+	let ed25519 = curve25519_dalek::edwards::CompressedEdwardsY(pk.0);
+	let x25519 = ed25519.decompress().ok_or(Error::BadData)?.to_montgomery();
+	let montgomery = x25519_dalek::PublicKey::from(x25519.to_bytes());
+	encrypt_x25519(&montgomery, plaintext)
+}
+
+/// Decrypt with the given x25519 secret key.
+pub fn decrypt_x25519(sk: &SecretKey, encrypted: &[u8]) -> Result<Vec<u8>, Error> {
+	if encrypted.len() < PK_LEN + NONCE_LEN {
+		return Err(Error::BadData)
+	}
+	let mut ephemeral_pk: [u8; PK_LEN] = Default::default();
+	ephemeral_pk.copy_from_slice(&encrypted[0..PK_LEN]);
+	let ephemeral_pk = PublicKey::from(ephemeral_pk);
+
+	let mut shared_secret = sk.diffie_hellman(&ephemeral_pk).to_bytes().to_vec();
+	shared_secret.extend_from_slice(ephemeral_pk.as_bytes());
+
+	let aes_key = kdf(&shared_secret);
+
+	let nonce = &encrypted[PK_LEN..PK_LEN + NONCE_LEN];
+	aes_decrypt(&aes_key, &nonce, &encrypted[PK_LEN + NONCE_LEN..])
+}
+
+/// Decrypt with the given ed25519 key pair.
+pub fn decrypt_ed25519(pair: &sp_core::ed25519::Pair, encrypted: &[u8]) -> Result<Vec<u8>, Error> {
+	let raw = pair.to_raw_vec();
+	let hash: [u8; 32] = sha2::Sha512::digest(&raw).as_slice()[..32]
+		.try_into()
+		.map_err(|_| Error::Decryption)?;
+	let secret = x25519_dalek::StaticSecret::from(hash);
+	decrypt_x25519(&secret, encrypted)
+}
+
+#[cfg(test)]
+mod test {
+	use super::*;
+	use rand::rngs::OsRng;
+	use sp_core::crypto::Pair;
+
+	#[test]
+	fn basic_x25519_encryption() {
+		let sk = SecretKey::new(OsRng);
+		let pk = PublicKey::from(&sk);
+
+		let plain_message = b"An important secret message";
+		let encrypted = encrypt_x25519(&pk, plain_message).unwrap();
+
+		let decrypted = decrypt_x25519(&sk, &encrypted).unwrap();
+		assert_eq!(plain_message, decrypted.as_slice());
+	}
+
+	#[test]
+	fn basic_ed25519_encryption() {
+		let (pair, _) = sp_core::ed25519::Pair::generate();
+		let pk = pair.into();
+
+		let plain_message = b"An important secret message";
+		let encrypted = encrypt_ed25519(&pk, plain_message).unwrap();
+
+		let decrypted = decrypt_ed25519(&pair, &encrypted).unwrap();
+		assert_eq!(plain_message, decrypted.as_slice());
+	}
+
+	#[test]
+	fn fails_on_bad_data() {
+		let sk = SecretKey::new(OsRng);
+		let pk = PublicKey::from(&sk);
+
+		let plain_message = b"An important secret message";
+		let encrypted = encrypt_x25519(&pk, plain_message).unwrap();
+
+		assert_eq!(decrypt_x25519(&sk, &[]), Err(Error::BadData));
+		assert_eq!(
+			decrypt_x25519(&sk, &encrypted[0..super::PK_LEN + super::NONCE_LEN - 1]),
+			Err(Error::BadData)
+		);
+	}
+}

substrate/primitives/statement-store/src/lib.rs

@@ -49,6 +49,8 @@ pub use store_api::{
 	Error, NetworkPriority, Result, StatementSource, StatementStore, SubmitResult,
 };
 
+#[cfg(feature = "std")]
+mod ecies;
 pub mod runtime_api;
 #[cfg(feature = "std")]
 mod store_api;
@@ -61,12 +63,17 @@ mod sr25519 {
 	pub type Public = app_sr25519::Public;
 }
 
-mod ed25519 {
+/// Statement-store specific ed25519 crypto primitives.
+pub mod ed25519 {
 	mod app_ed25519 {
 		use sp_application_crypto::{app_crypto, ed25519, key_types::STATEMENT};
 		app_crypto!(ed25519, STATEMENT);
 	}
+	/// Statement-store specific ed25519 public key.
 	pub type Public = app_ed25519::Public;
+	/// Statement-store specific ed25519 key pair.
+	#[cfg(feature = "std")]
+	pub type Pair = app_ed25519::Pair;
 }
 
 mod ecdsa {
@@ -507,6 +514,28 @@ impl Statement {
 		}
 		output
 	}
+
+	/// Encrypt give data with given key and store both in the statements.
+	#[cfg(feature = "std")]
+	pub fn encrypt(
+		&mut self,
+		data: &[u8],
+		key: &sp_core::ed25519::Public,
+	) -> core::result::Result<(), ecies::Error> {
+		let encrypted = ecies::encrypt_ed25519(key, data)?;
+		self.data = Some(encrypted);
+		self.decryption_key = Some((*key).into());
+		Ok(())
+	}
+
+	/// Decrypt data (if any) with the given private key.
+	#[cfg(feature = "std")]
+	pub fn decrypt_private(
+		&self,
+		key: &sp_core::ed25519::Pair,
+	) -> core::result::Result<Option<Vec<u8>>, ecies::Error> {
+		self.data.as_ref().map(|d| ecies::decrypt_ed25519(key, d)).transpose()
+	}
 }
 
 #[cfg(test)]
@@ -615,4 +644,18 @@ mod test {
 		statement.remove_proof();
 		assert_eq!(statement.verify_signature(), SignatureVerificationResult::NoSignature);
 	}
+
+	#[test]
+	fn encrypt_decrypt() {
+		let mut statement = Statement::new();
+		let (pair, _) = sp_core::ed25519::Pair::generate();
+		let plain = b"test data".to_vec();
+
+		//let sr25519_kp = sp_core::sr25519::Pair::from_string("//Alice", None).unwrap();
+		statement.encrypt(&plain, &pair.public()).unwrap();
+		assert_ne!(plain.as_slice(), statement.data().unwrap().as_slice());
+
+		let decrypted = statement.decrypt_private(&pair).unwrap();
+		assert_eq!(decrypted, Some(plain));
+	}
 }