Pairings (closes #3)

src/bnwrap.cpp

@@ -17,12 +17,18 @@ using namespace libsnark;
 typedef Fr<alt_bn128_pp> FieldT;
 
 extern "C" void bnwrap_init() {
+    libsnark::inhibit_profiling_info = true;
+    libsnark::inhibit_profiling_counters = true;
     assert(sodium_init() != -1);
     init_alt_bn128_params();
 }
 
 // Fr
 
+extern "C" FieldT bnwrap_Fr_random() {
+    return FieldT::random_element();
+}
+
 extern "C" FieldT bnwrap_Fr_from(const char *a) {
     return FieldT(a);
 }
@@ -118,3 +124,13 @@ extern "C" alt_bn128_G2 bnwrap_G2_neg(alt_bn128_G2 *p) {
 extern "C" alt_bn128_G2 bnwrap_G2_scalarmul(alt_bn128_G2 *p, FieldT *q) {
     return (*q) * (*p);
 }
+
+// Pairing
+
+extern "C" alt_bn128_GT bnwrap_gt_exp(alt_bn128_GT *p, FieldT *s) {
+    return (*p) ^ (*s);
+}
+
+extern "C" alt_bn128_GT bnwrap_pairing(alt_bn128_G1 *p, alt_bn128_G2 *q) {
+    return alt_bn128_reduced_pairing(*p, *q);
+}

src/curve/fr.rs

@@ -8,6 +8,7 @@ use std::ffi::CString;
 pub struct Fr([u64; 4]);
 
 extern "C" {
+    fn bnwrap_Fr_random() -> Fr;
     fn bnwrap_Fr_from(s: *const c_char) -> Fr;
     fn bnwrap_Fr_add(a: *const Fr, b: *const Fr) -> Fr;
     fn bnwrap_Fr_mul(a: *const Fr, b: *const Fr) -> Fr;
@@ -16,6 +17,10 @@ extern "C" {
 }
 
 impl Fr {
+    pub fn random() -> Self {
+        unsafe { bnwrap_Fr_random() }
+    }
+
     pub fn from_str(s: &str) -> Self {
         for c in s.chars() {
             if c != '0' &&

src/curve/gt.rs

@@ -1,6 +1,21 @@
+use std::ops::Mul;
+use super::Fr;
+
 #[derive(Copy, Clone, Eq, PartialEq)]
 #[repr(C)]
 pub struct Gt {
     a: [u64; 4 * 6],
     b: [u64; 4 * 6]
 }
+
+extern "C" {
+    fn bnwrap_gt_exp(p: *const Gt, s: *const Fr) -> Gt;
+}
+
+impl Mul<Fr> for Gt {
+    type Output = Gt;
+
+    fn mul(self, other: Fr) -> Gt {
+        unsafe { bnwrap_gt_exp(&self, &other) }
+    }
+}

src/curve/mod.rs

@@ -13,6 +13,7 @@ pub use self::g2::G2;
 
 extern "C" {
     fn bnwrap_init();
+    fn bnwrap_pairing(p: *const G1, q: *const G2) -> Gt;
 }
 
 lazy_static! {
@@ -29,6 +30,10 @@ pub fn initialize() {
     }
 }
 
+pub fn pairing(p: &G1, q: &G2) -> Gt {
+    unsafe { bnwrap_pairing(p, q) }
+}
+
 pub trait GroupElement: Sized +
                         Copy +
                         Clone +
@@ -43,6 +48,27 @@ pub trait GroupElement: Sized +
     fn is_zero(&self) -> bool;
 }
 
+#[test]
+fn pairing_test() {
+    initialize();
+
+    for _ in 0..50 {
+        let p = G1::random();
+        let q = G2::random();
+        let s = Fr::random();
+
+        let sp = p * s;
+        let sq = q * s;
+
+        let a = pairing(&p, &q) * s;
+        let b = pairing(&sp, &q);
+        let c = pairing(&p, &sq);
+
+        assert!(a == b);
+        assert!(b == c);
+    }
+}
+
 mod test_groups {
     use super::{Fr, G1, G2, initialize, GroupElement};