Secretstore DKG protocol draft + distributed encryption/decryption tests (#4725)

* ECDKG protocol prototype

* added test for enc/dec math

* get rid of decryption_session

* added licenses

* fix after merge

* get rid of unused serde dependency

* doc

* decryption session [without commutative enc]

* failed_dec_session

* fixed tests

* added commen

* added more decryption session tests

* helper to localize an issue

* more computations to localize error

* decryption_session::SessionParams

* added tests for EC math to localize problem

ethkey/src/error.rs

@@ -51,6 +51,12 @@ impl fmt::Display for Error {
 	}
 }
 
+impl Into<String> for Error {
+	fn into(self) -> String {
+		format!("{}", self)
+	}
+}
+
 impl From<::secp256k1::Error> for Error {
 	fn from(e: ::secp256k1::Error) -> Error {
 		match e {

ethkey/src/math.rs

@@ -36,6 +36,17 @@ pub fn public_add(public: &mut Public, other: &Public) -> Result<(), Error> {
 	Ok(())
 }
 
+/// Inplace sub one public key from another (EC point - EC point)
+pub fn public_sub(public: &mut Public, other: &Public) -> Result<(), Error> {
+	let mut key_neg_other = to_secp256k1_public(other)?;
+	key_neg_other.mul_assign(&SECP256K1, &key::MINUS_ONE_KEY)?;
+
+	let mut key_public = to_secp256k1_public(public)?;
+	key_public.add_assign(&SECP256K1, &key_neg_other)?;
+	set_public(public, &key_public);
+	Ok(())
+}
+
 /// Return base point of secp256k1
 pub fn generation_point() -> Public {
 	let mut public_sec_raw = [0u8; 65];
@@ -64,3 +75,35 @@ fn set_public(public: &mut Public, key_public: &key::PublicKey) {
 	let key_public_serialized = key_public.serialize_vec(&SECP256K1, false);
 	public.copy_from_slice(&key_public_serialized[1..65]);
 }
+
+#[cfg(test)]
+mod tests {
+	use super::super::{Random, Generator};
+	use super::{public_add, public_sub};
+
+	#[test]
+	fn public_addition_is_commutative() {
+		let public1 = Random.generate().unwrap().public().clone();
+		let public2 = Random.generate().unwrap().public().clone();
+
+		let mut left = public1.clone();
+		public_add(&mut left, &public2).unwrap();
+
+		let mut right = public2.clone();
+		public_add(&mut right, &public1).unwrap();
+
+		assert_eq!(left, right);
+	}
+
+	#[test]
+	fn public_addition_is_reversible_with_subtraction() {
+		let public1 = Random.generate().unwrap().public().clone();
+		let public2 = Random.generate().unwrap().public().clone();
+
+		let mut sum = public1.clone();
+		public_add(&mut sum, &public2).unwrap();
+		public_sub(&mut sum, &public2).unwrap();
+
+		assert_eq!(sum, public1);
+	}
+}

ethkey/src/secret.rs

@@ -130,3 +130,54 @@ impl Deref for Secret {
 		&self.inner
 	}
 }
+
+#[cfg(test)]
+mod tests {
+	use std::str::FromStr;
+	use super::super::{Random, Generator};
+	use super::Secret;
+
+	#[test]
+	fn multiplicating_secret_inversion_with_secret_gives_one() {
+		let secret = Random.generate().unwrap().secret().clone();
+		let mut inversion = secret.clone();
+		inversion.inv().unwrap();
+		inversion.mul(&secret).unwrap();
+		assert_eq!(inversion, Secret::from_str("0000000000000000000000000000000000000000000000000000000000000001").unwrap());
+	}
+
+	#[test]
+	fn secret_inversion_is_reversible_with_inversion() {
+		let secret = Random.generate().unwrap().secret().clone();
+		let mut inversion = secret.clone();
+		inversion.inv().unwrap();
+		inversion.inv().unwrap();
+		assert_eq!(inversion, secret);
+	}
+
+	#[test]
+	fn secret_pow() {
+		let secret = Random.generate().unwrap().secret().clone();
+
+		let mut pow0 = secret.clone();
+		pow0.pow(0).unwrap();
+		assert_eq!(pow0, Secret::from_str("0000000000000000000000000000000000000000000000000000000000000001").unwrap());
+
+		let mut pow1 = secret.clone();
+		pow1.pow(1).unwrap();
+		assert_eq!(pow1, secret);
+
+		let mut pow2 = secret.clone();
+		pow2.pow(2).unwrap();
+		let mut pow2_expected = secret.clone();
+		pow2_expected.mul(&secret).unwrap();
+		assert_eq!(pow2, pow2_expected);
+
+		let mut pow3 = secret.clone();
+		pow3.pow(3).unwrap();
+		let mut pow3_expected = secret.clone();
+		pow3_expected.mul(&secret).unwrap();
+		pow3_expected.mul(&secret).unwrap();
+		assert_eq!(pow3, pow3_expected);
+	}
+}