optional dependency on secp256k1 for ethcrypto (#8109)

* optional dependency on secp256k1 for ethcrypto

* README

ethcrypto/Cargo.toml

@@ -6,7 +6,11 @@ authors = ["Parity Technologies <admin@parity.io>"]
 [dependencies]
 rust-crypto = "0.2.36"
 tiny-keccak = "1.3"
-eth-secp256k1 = { git = "https://github.com/paritytech/rust-secp256k1" }
-ethkey = { path = "../ethkey" }
+eth-secp256k1 = { git = "https://github.com/paritytech/rust-secp256k1", optional = true }
+ethkey = { path = "../ethkey", optional = true }
 ethereum-types = "0.2"
 subtle = "0.5"
+
+[features]
+default = ["secp256k1"]
+secp256k1 = ["eth-secp256k1", "ethkey"]

ethcrypto/README.md

@@ -0,0 +1,5 @@
+# Ethcrypto
+
+General cryptographic utilities for Ethereum.
+
+By default, this library is compiled with the `secp256k1` feature, which provides ECDH and ECIES capability on that curve. It can be compiled without to avoid a dependency on the `libsecp256k1` library.

ethcrypto/src/lib.rs

@@ -18,17 +18,22 @@
 
 extern crate crypto as rcrypto;
 extern crate ethereum_types;
-extern crate ethkey;
-extern crate secp256k1;
 extern crate subtle;
 extern crate tiny_keccak;
 
+#[cfg(feature = "secp256k1")]
+extern crate secp256k1;
+#[cfg(feature = "secp256k1")]
+extern crate ethkey;
+
 use std::fmt;
 use tiny_keccak::Keccak;
 use rcrypto::pbkdf2::pbkdf2;
 use rcrypto::scrypt::{scrypt, ScryptParams};
 use rcrypto::sha2::Sha256;
 use rcrypto::hmac::Hmac;
+
+#[cfg(feature = "secp256k1")]
 use secp256k1::Error as SecpError;
 
 pub const KEY_LENGTH: usize = 32;
@@ -59,6 +64,7 @@ impl fmt::Display for ScryptError {
 
 #[derive(PartialEq, Debug)]
 pub enum Error {
+	#[cfg(feature = "secp256k1")]
 	Secp(SecpError),
 	Scrypt(ScryptError),
 	InvalidMessage,
@@ -73,6 +79,7 @@ impl From<ScryptError> for Error {
 impl fmt::Display for Error {
 	fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
 		let s = match *self {
+			#[cfg(feature = "secp256k1")]
 			Error::Secp(ref err) => err.to_string(),
 			Error::Scrypt(ref err) => err.to_string(),
 			Error::InvalidMessage => "Invalid message".into(),
@@ -88,6 +95,7 @@ impl Into<String> for Error {
 	}
 }
 
+#[cfg(feature = "secp256k1")]
 impl From<SecpError> for Error {
 	fn from(e: SecpError) -> Self {
 		Error::Secp(e)
@@ -174,6 +182,7 @@ pub mod aes {
 }
 
 /// ECDH functions
+#[cfg(feature = "secp256k1")]
 pub mod ecdh {
 	use secp256k1::{ecdh, key, Error as SecpError};
 	use ethkey::{Secret, Public, SECP256K1};
@@ -198,6 +207,7 @@ pub mod ecdh {
 }
 
 /// ECIES function
+#[cfg(feature = "secp256k1")]
 pub mod ecies {
 	use rcrypto::digest::Digest;
 	use rcrypto::sha2::Sha256;

ethkey/src/extended.rs

@@ -207,7 +207,6 @@ impl ExtendedKeyPair {
 // Work is based on BIP0032
 // https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki
 mod derivation {
-
 	use rcrypto::hmac::Hmac;
 	use rcrypto::mac::Mac;
 	use rcrypto::sha2::Sha512;