Support different bigint implementations (#106)

* Sync

* Replace BigInt type alias with a structure

* Sync

* Add doc comments

* Add option to use num-bigint

* Move common macros to separate module

* Implement remaining traits

* Write more docs & examples

* Remove redundant tests

* Update remaining crate to support new BigInt

* Bump version, update README, write more docs, fix missing trait

* Add checking / searching primes capabilities

* Remove Sign from exporting / importing

* Implement a few more traits

* Remove ambiguous method is_even from NumberTests

* Implement more ops

* Impl Display trait

* Fix clippy warnings

* Delete commented out tests

* Return back old samplabe implementation

* Remove Sign enum

* Put warning in README

* Fix doctests

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "curv"
-version = "0.5.9"
+version = "0.6.0"
 edition = "2018"
 authors = ["Omer Shlomovits"]
 license = "MIT"
@@ -22,20 +22,21 @@ generic-array = "0.14"
 hex = "^0.3"
 hmac = "0.7.1"
 merkle-sha3 = "^0.1"
+lazy_static = "1.4.0"
 num-traits = "0.2"
+num-integer = "0.1"
 pairing-plus = "0.19"
 rand = "0.6"
 ring-algorithm = "0.2.3"
 rust-crypto = "^0.2"
-serde = "1.0"
+serde = { version = "1.0", features = ["derive"] }
 serde_derive = "1.0"
 sha2 = "0.8.0"
 sha3 = "0.8.2"
 zeroize = "0.10"
 
-[dependencies.rust-gmp-kzen]
-version = "0.5.0"
-features = ["serde_support"]
+rust-gmp-kzen = { version = "0.5", features = ["serde_support"], optional = true }
+num-bigint = { version = "0.3", features = ["serde"], optional = true }
 
 [dependencies.secp256k1]
 version = "0.15.3"
@@ -50,3 +51,7 @@ bincode = "1.1"
 serde_json = "1.0"
 paste = "1.0.2"
 proptest = "0.10"
+proptest-derive = "0.2"
+
+[features]
+default = ["rust-gmp-kzen"]

README.md

@@ -37,6 +37,22 @@ attacks as possible (see audit report).
 ### Build
 Use `cargo build` to build everything including curve implementations, cryptoprimitives, BigInt, etc.
 
+### Big integer implementation
+The library supports a couple of bigint implementations and can easily switch between them.
+You can choose any one which you prefer by specifying a feature:
+* **rust-gmp-kzen**, uses GMP bindings, requires GMP to be installed on a machine. Used by default.
+* **num-bigint**, Rust's pure implementation of big integer. In order to use it, put in Cargo.toml:
+  ```toml
+  [dependencies.curv]
+  git = "https://github.com/ZenGo-X/curv"
+  tag = "v0.6.0"
+  default-features = false
+  features = ["num-bigint"]
+  ```
+
+  **_Warning:_** `num-bigint` support is experimental and should not be used in production. For this
+  bigint implementation, we use prime numbers generator which is not considered secure.
+
 ### Examples
 The library includes some basic examples to get you going. To run them: 
 `cargo run --example EXAMPLE_NAME -- CURVE_NAME`

examples/pedersen_commitment.rs

@@ -1,5 +1,5 @@
+use curv::arithmetic::{traits::*, BigInt};
 use curv::elliptic::curves::traits::ECPoint;
-use curv::BigInt;
 
 use std::fmt::Debug;
 
@@ -18,7 +18,6 @@ pub fn ped_com<P>(message: &BigInt)
 where
     P: ECPoint + Debug,
 {
-    use curv::arithmetic::traits::Samplable;
     use curv::cryptographic_primitives::commitments::pedersen_commitment::PedersenCommitment;
     use curv::cryptographic_primitives::commitments::traits::Commitment;
 
@@ -38,7 +37,7 @@ where
 fn main() {
     let message = "commit me!";
     let message_bytes = message.as_bytes();
-    let _message_bn = BigInt::from(message_bytes);
+    let _message_bn = BigInt::from_bytes(message_bytes);
     let curve_name = std::env::args().nth(1);
     match curve_name.as_deref() {
         Some("secp256k1") => ped_com::<curv::elliptic::curves::secp256_k1::GE>(&_message_bn),