Bulletproofs: verification speedup

src/ringct/bulletproofs.cc

@@ -905,7 +905,7 @@ bool bulletproof_VERIFY(const std::vector<const Bulletproof*> &proofs)
   rct::key m_y0 = rct::zero(), y1 = rct::zero();
   int proof_data_index = 0;
   rct::keyV w_cache;
-  rct::keyV proof8_V, proof8_L, proof8_R;
+  std::vector<ge_p3> proof8_V, proof8_L, proof8_R;
   for (const Bulletproof *p: proofs)
   {
     const Bulletproof &proof = *p;
@@ -918,13 +918,17 @@ bool bulletproof_VERIFY(const std::vector<const Bulletproof*> &proofs)
     const rct::key weight_z = rct::skGen();
 
     // pre-multiply some points by 8
-    proof8_V.resize(proof.V.size()); for (size_t i = 0; i < proof.V.size(); ++i) proof8_V[i] = rct::scalarmult8(proof.V[i]);
+    proof8_V.resize(proof.V.size()); for (size_t i = 0; i < proof.V.size(); ++i) rct::scalarmult8(proof8_V[i], proof.V[i]);
-    proof8_L.resize(proof.L.size()); for (size_t i = 0; i < proof.L.size(); ++i) proof8_L[i] = rct::scalarmult8(proof.L[i]);
+    proof8_L.resize(proof.L.size()); for (size_t i = 0; i < proof.L.size(); ++i) rct::scalarmult8(proof8_L[i], proof.L[i]);
-    proof8_R.resize(proof.R.size()); for (size_t i = 0; i < proof.R.size(); ++i) proof8_R[i] = rct::scalarmult8(proof.R[i]);
+    proof8_R.resize(proof.R.size()); for (size_t i = 0; i < proof.R.size(); ++i) rct::scalarmult8(proof8_R[i], proof.R[i]);
-    rct::key proof8_T1 = rct::scalarmult8(proof.T1);
+    ge_p3 proof8_T1;
-    rct::key proof8_T2 = rct::scalarmult8(proof.T2);
+    ge_p3 proof8_T2;
-    rct::key proof8_S = rct::scalarmult8(proof.S);
+    ge_p3 proof8_S;
-    rct::key proof8_A = rct::scalarmult8(proof.A);
+    ge_p3 proof8_A;
+    rct::scalarmult8(proof8_T1, proof.T1);
+    rct::scalarmult8(proof8_T2, proof.T2);
+    rct::scalarmult8(proof8_S, proof.S);
+    rct::scalarmult8(proof8_A, proof.A);
 
     PERF_TIMER_START_BP(VERIFY_line_61);
     sc_mulsub(m_y0.bytes, proof.taux.bytes, weight_y.bytes, m_y0.bytes);

src/ringct/rctOps.cpp

@@ -408,6 +408,18 @@ namespace rct {
         return res;
     }
 
+    //Computes 8P without byte conversion
+    void scalarmult8(ge_p3 &res, const key &P)
+    {
+        ge_p3 p3;
+        CHECK_AND_ASSERT_THROW_MES_L1(ge_frombytes_vartime(&p3, P.bytes) == 0, "ge_frombytes_vartime failed at "+boost::lexical_cast<std::string>(__LINE__));
+        ge_p2 p2;
+        ge_p3_to_p2(&p2, &p3);
+        ge_p1p1 p1;
+        ge_mul8(&p1, &p2);
+        ge_p1p1_to_p3(&res, &p1);
+    }
+
     //Computes lA where l is the curve order
     bool isInMainSubgroup(const key & A) {
         ge_p3 p3;

src/ringct/rctOps.h

@@ -124,6 +124,7 @@ namespace rct {
     key scalarmultH(const key & a);
     // multiplies a point by 8
     key scalarmult8(const key & P);
+    void scalarmult8(ge_p3 &res, const key & P);
     // checks a is in the main subgroup (ie, not a small one)
     bool isInMainSubgroup(const key & a);
 

tests/performance_tests/crypto_ops.h

@@ -48,6 +48,7 @@ enum test_op
   op_scalarmultKey,
   op_scalarmultH,
   op_scalarmult8,
+  op_scalarmult8_p3,
   op_ge_dsm_precomp,
   op_ge_double_scalarmult_base_vartime,
   op_ge_double_scalarmult_precomp_vartime,
@@ -105,6 +106,7 @@ public:
       case op_scalarmultKey: rct::scalarmultKey(point0, scalar0); break;
       case op_scalarmultH: rct::scalarmultH(scalar0); break;
       case op_scalarmult8: rct::scalarmult8(point0); break;
+      case op_scalarmult8_p3: rct::scalarmult8(p3_0,point0); break;
       case op_ge_dsm_precomp: ge_dsm_precomp(dsmp, &p3_0); break;
       case op_ge_double_scalarmult_base_vartime: ge_double_scalarmult_base_vartime(&tmp_p2, scalar0.bytes, &p3_0, scalar1.bytes); break;
       case op_ge_double_scalarmult_precomp_vartime: ge_double_scalarmult_precomp_vartime(&tmp_p2, scalar0.bytes, &p3_0, scalar1.bytes, precomp0); break;

tests/performance_tests/main.cpp

@@ -254,6 +254,7 @@ int main(int argc, char** argv)
   TEST_PERFORMANCE1(filter, p, test_crypto_ops, op_scalarmultKey);
   TEST_PERFORMANCE1(filter, p, test_crypto_ops, op_scalarmultH);
   TEST_PERFORMANCE1(filter, p, test_crypto_ops, op_scalarmult8);
+  TEST_PERFORMANCE1(filter, p, test_crypto_ops, op_scalarmult8_p3);
   TEST_PERFORMANCE1(filter, p, test_crypto_ops, op_ge_dsm_precomp);
   TEST_PERFORMANCE1(filter, p, test_crypto_ops, op_ge_double_scalarmult_base_vartime);
   TEST_PERFORMANCE1(filter, p, test_crypto_ops, op_ge_double_scalarmult_precomp_vartime);

tests/unit_tests/ringct.cpp

@@ -1077,8 +1077,16 @@ TEST(ringct, H)
 
 TEST(ringct, mul8)
 {
+  ge_p3 p3;
+  rct::key key;
   ASSERT_EQ(rct::scalarmult8(rct::identity()), rct::identity());
+  rct::scalarmult8(p3,rct::identity());
+  ge_p3_tobytes(key.bytes, &p3);
+  ASSERT_EQ(key, rct::identity());
   ASSERT_EQ(rct::scalarmult8(rct::H), rct::scalarmultKey(rct::H, rct::EIGHT));
+  rct::scalarmult8(p3,rct::H);
+  ge_p3_tobytes(key.bytes, &p3);
+  ASSERT_EQ(key, rct::scalarmultKey(rct::H, rct::EIGHT));
   ASSERT_EQ(rct::scalarmultKey(rct::scalarmultKey(rct::H, rct::INV_EIGHT), rct::EIGHT), rct::H);
 }