precalc the ge_p3 representation of H

5 files changed, 26 insertions, 14 deletions

diff --git a/src/crypto/crypto-ops-data.c b/src/crypto/crypto-ops-data.c
index 4ff4310de..1f77513ca 100644
--- a/src/crypto/crypto-ops-data.c
+++ b/src/crypto/crypto-ops-data.c
@@ -871,3 +871,9 @@ const fe fe_fffb2 = {8166131, -6741800, -17040804, 3154616, 21461005, 1466302, -
 const fe fe_fffb3 = {-13620103, 14639558, 4532995, 7679154, 16815101, -15883539, -22863840, -14813421, 13716513, -6477756}; /* sqrt(-sqrt(-1) * A * (A + 2)) */
 const fe fe_fffb4 = {-21786234, -12173074, 21573800, 4524538, -4645904, 16204591, 8012863, -8444712, 3212926, 6885324}; /* sqrt(sqrt(-1) * A * (A + 2)) */
 const ge_p3 ge_p3_identity = { {0}, {1, 0}, {1, 0}, {0} };
+const ge_p3 ge_p3_H = {
+  {7329926, -15101362, 31411471, 7614783, 27996851, -3197071, -11157635, -6878293, 466949, -7986503},
+  {5858699, 5096796, 21321203, -7536921, -5553480, -11439507, -5627669, 15045946, 19977121, 5275251},
+  {1, 0, 0, 0, 0, 0, 0, 0, 0, 0},
+  {23443568, -5110398, -8776029, -4345135, 6889568, -14710814, 7474843, 3279062, 14550766, -7453428}
+};
diff --git a/src/crypto/crypto-ops.h b/src/crypto/crypto-ops.h
index dc3c60794..52854889f 100644
--- a/src/crypto/crypto-ops.h
+++ b/src/crypto/crypto-ops.h
@@ -140,6 +140,7 @@ extern const fe fe_fffb2;
 extern const fe fe_fffb3;
 extern const fe fe_fffb4;
 extern const ge_p3 ge_p3_identity;
+extern const ge_p3 ge_p3_H;
 void ge_fromfe_frombytes_vartime(ge_p2 *, const unsigned char *);
 void sc_0(unsigned char *);
 void sc_reduce32(unsigned char *);
diff --git a/src/ringct/bulletproofs.cc b/src/ringct/bulletproofs.cc
index dc5918738..884c99537 100644
--- a/src/ringct/bulletproofs.cc
+++ b/src/ringct/bulletproofs.cc
@@ -521,8 +521,8 @@ Bulletproof bulletproof_PROVE(const rct::key &sv, const rct::key &gamma)
   // PAPER LINES 47-48
   rct::key tau1 = rct::skGen(), tau2 = rct::skGen();
 
-  rct::key T1 = rct::addKeys(rct::scalarmultKey(rct::H, t1), rct::scalarmultBase(tau1));
-  rct::key T2 = rct::addKeys(rct::scalarmultKey(rct::H, t2), rct::scalarmultBase(tau2));
+  rct::key T1 = rct::addKeys(rct::scalarmultH(t1), rct::scalarmultBase(tau1));
+  rct::key T2 = rct::addKeys(rct::scalarmultH(t2), rct::scalarmultBase(tau2));
 
   // PAPER LINES 49-51
   rct::key x = hash_cache_mash(hash_cache, z, T1, T2);
@@ -592,10 +592,10 @@ Bulletproof bulletproof_PROVE(const rct::key &sv, const rct::key &gamma)
     // PAPER LINES 18-19
     L[round] = vector_exponent_custom(slice(Gprime, nprime, Gprime.size()), slice(Hprime, 0, nprime), slice(aprime, 0, nprime), slice(bprime, nprime, bprime.size()));
     sc_mul(tmp.bytes, cL.bytes, x_ip.bytes);
-    rct::addKeys(L[round], L[round], rct::scalarmultKey(rct::H, tmp));
+    rct::addKeys(L[round], L[round], rct::scalarmultH(tmp));
     R[round] = vector_exponent_custom(slice(Gprime, 0, nprime), slice(Hprime, nprime, Hprime.size()), slice(aprime, nprime, aprime.size()), slice(bprime, 0, nprime));
     sc_mul(tmp.bytes, cR.bytes, x_ip.bytes);
-    rct::addKeys(R[round], R[round], rct::scalarmultKey(rct::H, tmp));
+    rct::addKeys(R[round], R[round], rct::scalarmultH(tmp));
 
     // PAPER LINES 21-22
     w[round] = hash_cache_mash(hash_cache, L[round], R[round]);
@@ -764,8 +764,8 @@ Bulletproof bulletproof_PROVE(const rct::keyV &sv, const rct::keyV &gamma)
   // PAPER LINES 47-48
   rct::key tau1 = rct::skGen(), tau2 = rct::skGen();
 
-  rct::key T1 = rct::addKeys(rct::scalarmultKey(rct::H, t1), rct::scalarmultBase(tau1));
-  rct::key T2 = rct::addKeys(rct::scalarmultKey(rct::H, t2), rct::scalarmultBase(tau2));
+  rct::key T1 = rct::addKeys(rct::scalarmultH(t1), rct::scalarmultBase(tau1));
+  rct::key T2 = rct::addKeys(rct::scalarmultH(t2), rct::scalarmultBase(tau2));
 
   // PAPER LINES 49-51
   rct::key x = hash_cache_mash(hash_cache, z, T1, T2);
@@ -842,10 +842,10 @@ Bulletproof bulletproof_PROVE(const rct::keyV &sv, const rct::keyV &gamma)
     // PAPER LINES 18-19
     L[round] = vector_exponent_custom(slice(Gprime, nprime, Gprime.size()), slice(Hprime, 0, nprime), slice(aprime, 0, nprime), slice(bprime, nprime, bprime.size()));
     sc_mul(tmp.bytes, cL.bytes, x_ip.bytes);
-    rct::addKeys(L[round], L[round], rct::scalarmultKey(rct::H, tmp));
+    rct::addKeys(L[round], L[round], rct::scalarmultH(tmp));
     R[round] = vector_exponent_custom(slice(Gprime, 0, nprime), slice(Hprime, nprime, Hprime.size()), slice(aprime, nprime, aprime.size()), slice(bprime, 0, nprime));
     sc_mul(tmp.bytes, cR.bytes, x_ip.bytes);
-    rct::addKeys(R[round], R[round], rct::scalarmultKey(rct::H, tmp));
+    rct::addKeys(R[round], R[round], rct::scalarmultH(tmp));
 
     // PAPER LINES 21-22
     w[round] = hash_cache_mash(hash_cache, L[round], R[round]);
@@ -964,7 +964,7 @@ bool bulletproof_VERIFY(const std::vector<const Bulletproof*> &proofs)
       sc_muladd(tmp.bytes, z.bytes, ip1y.bytes, k.bytes);
       std::vector<MultiexpData> multiexp_data;
       multiexp_data.reserve(3+proof.V.size());
-      multiexp_data.emplace_back(tmp, rct::H);
+      multiexp_data.emplace_back(tmp, ge_p3_H);
       for (size_t j = 0; j < proof.V.size(); j++)
       {
         multiexp_data.emplace_back(zpow[j+2], proof.V[j]);
@@ -980,7 +980,7 @@ bool bulletproof_VERIFY(const std::vector<const Bulletproof*> &proofs)
     {
       PERF_TIMER_START_BP(VERIFY_line_61rl_old);
       sc_muladd(tmp.bytes, z.bytes, ip1y.bytes, k.bytes);
-      L61Right = rct::scalarmultKey(rct::H, tmp);
+      L61Right = rct::scalarmultH(tmp);
       ge_p3 L61Right_p3;
       CHECK_AND_ASSERT_THROW_MES(ge_frombytes_vartime(&L61Right_p3, L61Right.bytes) == 0, "ge_frombytes_vartime failed");
       for (size_t j = 0; j+1 < proof.V.size(); j += 2)
@@ -1118,7 +1118,7 @@ bool bulletproof_VERIFY(const std::vector<const Bulletproof*> &proofs)
   sc_sub(tmp.bytes, rct::zero().bytes, z1.bytes);
   rct::addKeys(Y, Y, rct::scalarmultBase(tmp));
   rct::addKeys(Y, Y, Z2);
-  rct::addKeys(Y, Y, rct::scalarmultKey(rct::H, z3));
+  rct::addKeys(Y, Y, rct::scalarmultH(z3));
 
   std::vector<MultiexpData> multiexp_data;
   multiexp_data.reserve(2 * maxMN);
diff --git a/src/ringct/rctOps.cpp b/src/ringct/rctOps.cpp
index 50693bad7..fe0ad8747 100644
--- a/src/ringct/rctOps.cpp
+++ b/src/ringct/rctOps.cpp
@@ -193,10 +193,8 @@ namespace rct {
 
     //Computes aH where H= toPoint(cn_fast_hash(G)), G the basepoint
     key scalarmultH(const key & a) {
-        ge_p3 A;
         ge_p2 R;
-        CHECK_AND_ASSERT_THROW_MES_L1(ge_frombytes_vartime(&A, H.bytes) == 0, "ge_frombytes_vartime failed at "+boost::lexical_cast<std::string>(__LINE__));
-        ge_scalarmult(&R, a.bytes, &A);
+        ge_scalarmult(&R, a.bytes, &ge_p3_H);
         key aP;
         ge_tobytes(aP.bytes, &R);
         return aP;
diff --git a/tests/unit_tests/ringct.cpp b/tests/unit_tests/ringct.cpp
index d4e942176..360529b9e 100644
--- a/tests/unit_tests/ringct.cpp
+++ b/tests/unit_tests/ringct.cpp
@@ -1086,6 +1086,13 @@ TEST(ringct, zeroCommmit)
   ASSERT_EQ(z, manual);
 }
 
+TEST(ringct, H)
+{
+  ge_p3 p3;
+  ASSERT_EQ(ge_frombytes_vartime(&p3, rct::H.bytes), 0);
+  ASSERT_EQ(memcmp(&p3, &ge_p3_H, sizeof(ge_p3)), 0);
+}
+
 TEST(ringct, aggregated)
 {
   static const size_t N_PROOFS = 16;