From 8159d743efb6b7ce6111da894917f767999d61a4 Mon Sep 17 00:00:00 2001
From: Arkadiy Paronyan <arkady.paronyan@gmail.com>
Date: Thu, 18 Aug 2016 18:08:02 +0200
Subject: [PATCH] ECIES without MAC (#1948)

* Use random IV for ECIES AES

* ECIES encrypt/decrypt for a single message

* Derive IV from shared secret
---
 util/src/crypto.rs | 72 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 71 insertions(+), 1 deletion(-)

diff --git a/util/src/crypto.rs b/util/src/crypto.rs
index f4bc4c62e..298bc205e 100644
--- a/util/src/crypto.rs
+++ b/util/src/crypto.rs
@@ -311,6 +311,7 @@ pub mod ecies {
 	use hash::*;
 	use bytes::*;
 	use crypto::*;
+	use sha3::Hashable;
 
 	/// Encrypt a message with a public key
 	pub fn encrypt(public: &Public, shared_mac: &[u8], plain: &[u8]) -> Result<Bytes, CryptoError> {
@@ -334,9 +335,11 @@ pub mod ecies {
 		{
 			let msgd = &mut msg[1..];
 			r.public().copy_to(&mut msgd[0..64]);
+			let iv = H128::random();
+			iv.copy_to(&mut msgd[64..(64+16)]);
 			{
 				let cipher = &mut msgd[(64 + 16)..(64 + 16 + plain.len())];
-				aes::encrypt(ekey, &H128::new(), plain, cipher);
+				aes::encrypt(ekey, &iv, plain, cipher);
 			}
 			let mut hmac = Hmac::new(Sha256::new(), &mkey);
 			{
@@ -349,6 +352,33 @@ pub mod ecies {
 		Ok(msg)
 	}
 
+	/// Encrypt a message with a public key
+	pub fn encrypt_single_message(public: &Public, plain: &[u8]) -> Result<Bytes, CryptoError> {
+		use ::rcrypto::digest::Digest;
+		use ::rcrypto::sha2::Sha256;
+		let r = try!(KeyPair::create());
+		let z = try!(ecdh::agree(r.secret(), public));
+		let mut key = [0u8; 32];
+		let mut mkey = [0u8; 32];
+		kdf(&z, &[0u8; 0], &mut key);
+		let mut hasher = Sha256::new();
+		let mkey_material = &key[16..32];
+		hasher.input(mkey_material);
+		hasher.result(&mut mkey);
+		let ekey = &key[0..16];
+
+		let mut msgd = vec![0u8; (64 + plain.len())];
+		{
+			r.public().copy_to(&mut msgd[0..64]);
+			let iv = H128::from_slice(&z.sha3()[0..16]);
+			{
+				let cipher = &mut msgd[64..(64 + plain.len())];
+				aes::encrypt(ekey, &iv, plain, cipher);
+			}
+		}
+		Ok(msgd)
+	}
+
 	/// Decrypt a message with a secret key
 	pub fn decrypt(secret: &Secret, shared_mac: &[u8], encrypted: &[u8]) -> Result<Bytes, CryptoError> {
 		use ::rcrypto::digest::Digest;
@@ -394,6 +424,36 @@ pub mod ecies {
 		Ok(msg)
 	}
 
+	/// Decrypt single message with a secret key
+	pub fn decrypt_single_message(secret: &Secret, encrypted: &[u8]) -> Result<Bytes, CryptoError> {
+		use ::rcrypto::digest::Digest;
+		use ::rcrypto::sha2::Sha256;
+
+		let meta_len = 64;
+		if encrypted.len() < meta_len {
+			return Err(CryptoError::InvalidMessage); //invalid message: publickey
+		}
+
+		let e = encrypted;
+		let p = Public::from_slice(&e[0..64]);
+		let z = try!(ecdh::agree(secret, &p));
+		let mut key = [0u8; 32];
+		kdf(&z, &[0u8; 0], &mut key);
+		let ekey = &key[0..16];
+		let mkey_material = &key[16..32];
+		let mut hasher = Sha256::new();
+		let mut mkey = [0u8; 32];
+		hasher.input(mkey_material);
+		hasher.result(&mut mkey);
+
+		let clen = encrypted.len() - meta_len;
+		let cipher = &e[64..(64+clen)];
+		let mut msg = vec![0u8; clen];
+		let iv = H128::from_slice(&z.sha3()[0..16]);
+		aes::decrypt(ekey, &iv, cipher, &mut msg[..]);
+		Ok(msg)
+	}
+
 	fn kdf(secret: &Secret, s1: &[u8], dest: &mut [u8]) {
 		use ::rcrypto::digest::Digest;
 		use ::rcrypto::sha2::Sha256;
@@ -487,4 +547,14 @@ mod tests {
 		let decrypted = ecies::decrypt(kp.secret(), shared, &encrypted).unwrap();
 		assert_eq!(decrypted[..message.len()], message[..]);
 	}
+
+	#[test]
+	fn ecies_shared_single() {
+		let kp = KeyPair::create().unwrap();
+		let message = b"So many books, so little time";
+		let encrypted = ecies::encrypt_single_message(kp.public(), message).unwrap();
+		assert!(encrypted[..] != message[..]);
+		let decrypted = ecies::decrypt_single_message(kp.secret(), &encrypted).unwrap();
+		assert_eq!(decrypted[..message.len()], message[..]);
+	}
 }