WebAssembly compatibility

phase2/Cargo.toml

@@ -8,13 +8,13 @@ homepage = "https://github.com/ebfull/phase2"
 license = "MIT/Apache-2.0"
 repository = "https://github.com/ebfull/phase2"
 
+[lib]
+crate-type = ["cdylib", "lib"]
+
 [dependencies]
 rand = "0.4"
-bellman_ce = { path = "../bellman" }
 byteorder = "1"
 exitcode = "1.1.2"
-num_cpus = "1"
-crossbeam = "0.3"
 blake2-rfc = "0.2"
 blake2 = "0.6.1"
 serde = { version = "1.0", features = ["derive"] }
@@ -22,5 +22,20 @@ serde_json = "1.0"
 num-bigint = "0.2.3"
 num-traits = "0.2.8"
 itertools = "0.8.1"
-rust-crypto = "0.2"
 hex = "0.4.0"
+cfg-if = "0.1.10"
+bellman_ce = { path = "../bellman", default-features = false } # active features depend on build type
+
+# needed for native only but don't break wasm if present
+num_cpus = "1"
+crossbeam = "0.3"
+
+# needed for wasm only
+wasm-bindgen = { version = "0.2.58", optional = true }
+js-sys = { version = "0.3.35", optional = true }
+web-sys = { version = "0.3.35", features = ["console"], optional = true }
+console_error_panic_hook = { version = "0.1.6", optional = true }
+
+[features]
+default = ["bellman_ce/multicore"]
+wasm = ["wasm-bindgen", "js-sys", "web-sys", "console_error_panic_hook", "bellman_ce/wasm"]

phase2/README.md

@@ -2,6 +2,28 @@
 
 This library is still under development.
 
+## WebAssembly how-to
+
+Build wasm package using `wasm-pack build --release -- --no-default-features --features wasm`
+
+this will generate `./pkg` directory with wasm file and js bindings. After that you 
+can use this package in your browser application like so:
+
+```js
+async function main() {
+    const phase2 = await import("./pkg/phase2.js")
+    let data = await fetch('params')
+    data = await data.arrayBuffer()
+    data = new Uint8Array(data)
+    console.log('Source params', data)
+    const result = phase2.contribute(data)
+    console.log('Updated params', result)
+    // upload updated params
+}
+
+main().catch(console.error)
+``` 
+
 ## [Documentation](https://docs.rs/phase2/)
 
 ## Security Warnings

phase2/src/lib.rs

@@ -1,15 +1,15 @@
 #![allow(unused_imports)]
 
+#[macro_use]
+extern crate serde;
 extern crate bellman_ce;
 extern crate rand;
 extern crate byteorder;
 extern crate blake2_rfc;
 extern crate num_cpus;
 extern crate crossbeam;
-
-#[macro_use]
-extern crate serde;
-extern crate serde_json;
+extern crate cfg_if;
+use cfg_if::cfg_if;
 
 pub mod keypair;
 pub mod keypair_assembly;
@@ -17,3 +17,45 @@ pub mod hash_writer;
 pub mod parameters;
 pub mod utils;
 pub mod circom_circuit;
+
+cfg_if! {
+    if #[cfg(feature = "wasm")] {
+        extern crate serde_json;
+        extern crate js_sys;
+        extern crate web_sys;
+        extern crate wasm_bindgen;
+        extern crate console_error_panic_hook;
+        extern crate itertools;
+
+        use wasm_bindgen::prelude::*;
+        use itertools::Itertools;
+        use parameters::MPCParameters;
+        use std::io::{
+            Read,
+            Write,
+        };
+
+        macro_rules! log {
+            ($($t:tt)*) => (web_sys::console::log_1(&format_args!($($t)*).to_string().into()))
+        }
+
+        #[wasm_bindgen]
+        pub fn contribute(params: Vec<u8>) -> Result<Vec<u8>, JsValue> {
+            console_error_panic_hook::set_once();
+            let disallow_points_at_infinity = false;
+
+            log!("Initializing phase2");
+            let mut rng = &mut rand::XorShiftRng::new_unseeded(); // TODO: change this unsafe unseeded random (!)
+            let mut params = MPCParameters::read(&*params, disallow_points_at_infinity, true).expect("unable to read params");
+
+            log!("Contributing...");
+            let hash = params.contribute(&mut rng);
+            log!("Contribution hash: 0x{:02x}", hash.iter().format(""));
+
+            let mut output: Vec<u8> = vec![];
+            params.write(&mut output).expect("failed to write updated parameters");
+            log!("Returning parameters");
+            Ok(output)
+        }
+    }
+}

phase2/src/parameters.rs

@@ -4,6 +4,11 @@ extern crate byteorder;
 extern crate num_cpus;
 extern crate crossbeam;
 
+#[cfg(feature = "wasm")]
+use bellman_ce::singlecore::Worker;
+#[cfg(not(feature = "wasm"))]
+use bellman_ce::multicore::Worker;
+
 use byteorder::{
     BigEndian,
     ReadBytesExt,
@@ -46,8 +51,6 @@ use bellman_ce::pairing::{
     }
 };
 
-pub use bellman_ce::multicore::*;
-
 use bellman_ce::{
     Circuit,
     SynthesisError,
@@ -415,6 +418,7 @@ impl MPCParameters {
         // Generate a keypair
         let (pubkey, privkey) = keypair(rng, self);
 
+        #[cfg(not(feature = "wasm"))]
         fn batch_exp<C: CurveAffine>(bases: &mut [C], coeff: C::Scalar) {
             let coeff = coeff.into_repr();
 
@@ -459,6 +463,27 @@ impl MPCParameters {
             }
         }
 
+        #[cfg(feature = "wasm")]
+        fn batch_exp<C: CurveAffine>(bases: &mut [C], coeff: C::Scalar) {
+            let coeff = coeff.into_repr();
+
+            let mut projective = vec![C::Projective::zero(); bases.len()];
+
+            // Perform wNAF, placing results into `projective`.
+            let mut wnaf = Wnaf::new();
+            for (base, projective) in bases.iter_mut().zip(projective.iter_mut()) {
+                *projective = wnaf.base(base.into_projective(), 1).scalar(coeff);
+            }
+
+            // Perform batch normalization
+            C::Projective::batch_normalization(&mut projective);
+
+            // Turn it all back into affine points
+            for (projective, affine) in projective.iter().zip(bases.iter_mut()) {
+                *affine = projective.into_affine();
+            }
+        }
+
         let delta_inv = privkey.delta.inverse().expect("nonzero");
         let mut l = (&self.params.l[..]).to_vec();
         let mut h = (&self.params.h[..]).to_vec();