Merge pull request #6049

45fd72b Updated paper references (SarangNoether)
277003f Minor prover simplification (SarangNoether)

1 files changed, 27 insertions, 34 deletions

diff --git a/src/ringct/bulletproofs.cc b/src/ringct/bulletproofs.cc
index ff6fee95c..80ecc5593 100644
--- a/src/ringct/bulletproofs.cc
+++ b/src/ringct/bulletproofs.cc
@@ -27,6 +27,7 @@
 // THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 //
 // Adapted from Java code by Sarang Noether
+// Paper references are to https://eprint.iacr.org/2017/1066 (revision 1 July 2018)
 
 #include <stdlib.h>
 #include <boost/thread/mutex.hpp>
@@ -521,6 +522,7 @@ Bulletproof bulletproof_PROVE(const rct::keyV &sv, const rct::keyV &gamma)
   }
   PERF_TIMER_STOP_BP(PROVE_v);
 
+  // PAPER LINES 41-42
   PERF_TIMER_START_BP(PROVE_aLaR);
   for (size_t j = 0; j < M; ++j)
   {
@@ -566,14 +568,14 @@ try_again:
   rct::key hash_cache = rct::hash_to_scalar(V);
 
   PERF_TIMER_START_BP(PROVE_step1);
-  // PAPER LINES 38-39
+  // PAPER LINES 43-44
   rct::key alpha = rct::skGen();
   rct::key ve = vector_exponent(aL8, aR8);
   rct::key A;
   sc_mul(tmp.bytes, alpha.bytes, INV_EIGHT.bytes);
   rct::addKeys(A, ve, rct::scalarmultBase(tmp));
 
-  // PAPER LINES 40-42
+  // PAPER LINES 45-47
   rct::keyV sL = rct::skvGen(MN), sR = rct::skvGen(MN);
   rct::key rho = rct::skGen();
   ve = vector_exponent(sL, sR);
@@ -581,7 +583,7 @@ try_again:
   rct::addKeys(S, ve, rct::scalarmultBase(rho));
   S = rct::scalarmultKey(S, INV_EIGHT);
 
-  // PAPER LINES 43-45
+  // PAPER LINES 48-50
   rct::key y = hash_cache_mash(hash_cache, A, S);
   if (y == rct::zero())
   {
@@ -598,24 +600,20 @@ try_again:
   }
 
   // Polynomial construction by coefficients
+  // PAPER LINES 70-71
   rct::keyV l0 = vector_subtract(aL, z);
   const rct::keyV &l1 = sL;
 
-  // This computes the ugly sum/concatenation from PAPER LINE 65
   rct::keyV zero_twos(MN);
   const rct::keyV zpow = vector_powers(z, M+2);
-  for (size_t i = 0; i < MN; ++i)
+  for (size_t j = 0; j < M; ++j)
   {
-    zero_twos[i] = rct::zero();
-    for (size_t j = 1; j <= M; ++j)
-    {
-      if (i >= (j-1)*N && i < j*N)
+      for (size_t i = 0; i < N; ++i)
       {
-        CHECK_AND_ASSERT_THROW_MES(1+j < zpow.size(), "invalid zpow index");
-        CHECK_AND_ASSERT_THROW_MES(i-(j-1)*N < twoN.size(), "invalid twoN index");
-        sc_muladd(zero_twos[i].bytes, zpow[1+j].bytes, twoN[i-(j-1)*N].bytes, zero_twos[i].bytes);
+          CHECK_AND_ASSERT_THROW_MES(j+2 < zpow.size(), "invalid zpow index");
+          CHECK_AND_ASSERT_THROW_MES(i < twoN.size(), "invalid twoN index");
+          sc_mul(zero_twos[j*N+i].bytes,zpow[j+2].bytes,twoN[i].bytes);
       }
-    }
   }
 
   rct::keyV r0 = vector_add(aR, z);
@@ -624,7 +622,7 @@ try_again:
   r0 = vector_add(r0, zero_twos);
   rct::keyV r1 = hadamard(yMN, sR);
 
-  // Polynomial construction before PAPER LINE 46
+  // Polynomial construction before PAPER LINE 51
   rct::key t1_1 = inner_product(l0, r1);
   rct::key t1_2 = inner_product(l1, r0);
   rct::key t1;
@@ -634,7 +632,7 @@ try_again:
   PERF_TIMER_STOP_BP(PROVE_step1);
 
   PERF_TIMER_START_BP(PROVE_step2);
-  // PAPER LINES 47-48
+  // PAPER LINES 52-53
   rct::key tau1 = rct::skGen(), tau2 = rct::skGen();
 
   rct::key T1, T2;
@@ -648,7 +646,7 @@ try_again:
   ge_double_scalarmult_base_vartime_p3(&p3, tmp.bytes, &ge_p3_H, tmp2.bytes);
   ge_p3_tobytes(T2.bytes, &p3);
 
-  // PAPER LINES 49-51
+  // PAPER LINES 54-56
   rct::key x = hash_cache_mash(hash_cache, z, T1, T2);
   if (x == rct::zero())
   {
@@ -657,7 +655,7 @@ try_again:
     goto try_again;
   }
 
-  // PAPER LINES 52-53
+  // PAPER LINES 61-63
   rct::key taux;
   sc_mul(taux.bytes, tau1.bytes, x.bytes);
   rct::key xsq;
@@ -671,7 +669,7 @@ try_again:
   rct::key mu;
   sc_muladd(mu.bytes, x.bytes, rho.bytes, alpha.bytes);
 
-  // PAPER LINES 54-57
+  // PAPER LINES 58-60
   rct::keyV l = l0;
   l = vector_add(l, vector_scalar(l1, x));
   rct::keyV r = r0;
@@ -690,7 +688,7 @@ try_again:
   CHECK_AND_ASSERT_THROW_MES(test_t == t, "test_t check failed");
 #endif
 
-  // PAPER LINES 32-33
+  // PAPER LINE 6
   rct::key x_ip = hash_cache_mash(hash_cache, x, taux, mu, t);
   if (x_ip == rct::zero())
   {
@@ -725,20 +723,19 @@ try_again:
   PERF_TIMER_STOP_BP(PROVE_step3);
 
   PERF_TIMER_START_BP(PROVE_step4);
-  // PAPER LINE 13
   const rct::keyV *scale = &yinvpow;
   while (nprime > 1)
   {
-    // PAPER LINE 15
+    // PAPER LINE 20
     nprime /= 2;
 
-    // PAPER LINES 16-17
+    // PAPER LINES 21-22
     PERF_TIMER_START_BP(PROVE_inner_product);
     rct::key cL = inner_product(slice(aprime, 0, nprime), slice(bprime, nprime, bprime.size()));
     rct::key cR = inner_product(slice(aprime, nprime, aprime.size()), slice(bprime, 0, nprime));
     PERF_TIMER_STOP_BP(PROVE_inner_product);
 
-    // PAPER LINES 18-19
+    // PAPER LINES 23-24
     PERF_TIMER_START_BP(PROVE_LR);
     sc_mul(tmp.bytes, cL.bytes, x_ip.bytes);
     L[round] = cross_vector_exponent8(nprime, Gprime, nprime, Hprime, 0, aprime, 0, bprime, nprime, scale, &ge_p3_H, &tmp);
@@ -746,7 +743,7 @@ try_again:
     R[round] = cross_vector_exponent8(nprime, Gprime, 0, Hprime, nprime, aprime, nprime, bprime, 0, scale, &ge_p3_H, &tmp);
     PERF_TIMER_STOP_BP(PROVE_LR);
 
-    // PAPER LINES 21-22
+    // PAPER LINES 25-27
     w[round] = hash_cache_mash(hash_cache, L[round], R[round]);
     if (w[round] == rct::zero())
     {
@@ -755,7 +752,7 @@ try_again:
       goto try_again;
     }
 
-    // PAPER LINES 24-25
+    // PAPER LINES 29-30
     const rct::key winv = invert(w[round]);
     if (nprime > 1)
     {
@@ -765,7 +762,7 @@ try_again:
       PERF_TIMER_STOP_BP(PROVE_hadamard2);
     }
 
-    // PAPER LINES 28-29
+    // PAPER LINES 33-34
     PERF_TIMER_START_BP(PROVE_prime);
     aprime = vector_add(vector_scalar(slice(aprime, 0, nprime), w[round]), vector_scalar(slice(aprime, nprime, aprime.size()), winv));
     bprime = vector_add(vector_scalar(slice(bprime, 0, nprime), winv), vector_scalar(slice(bprime, nprime, bprime.size()), w[round]));
@@ -776,7 +773,6 @@ try_again:
   }
   PERF_TIMER_STOP_BP(PROVE_step4);
 
-  // PAPER LINE 58 (with inclusions from PAPER LINE 8 and PAPER LINE 20)
   return Bulletproof(std::move(V), A, S, T1, T2, taux, mu, std::move(L), std::move(R), aprime[0], bprime[0], t);
 }
 
@@ -810,7 +806,10 @@ struct proof_data_t
   size_t logM, inv_offset;
 };
 
-/* Given a range proof, determine if it is valid */
+/* Given a range proof, determine if it is valid
+ * This uses the method in PAPER LINES 95-105,
+ *   weighted across multiple proofs in a batch
+ */
 bool bulletproof_VERIFY(const std::vector<const Bulletproof*> &proofs)
 {
   init_exponents();
@@ -871,7 +870,6 @@ bool bulletproof_VERIFY(const std::vector<const Bulletproof*> &proofs)
     CHECK_AND_ASSERT_MES(rounds > 0, false, "Zero rounds");
 
     PERF_TIMER_START_BP(VERIFY_line_21_22);
-    // PAPER LINES 21-22
     // The inner product challenges are computed per round
     pd.w.resize(rounds);
     for (size_t i = 0; i < rounds; ++i)
@@ -929,7 +927,6 @@ bool bulletproof_VERIFY(const std::vector<const Bulletproof*> &proofs)
     rct::key proof8_A = rct::scalarmult8(proof.A);
 
     PERF_TIMER_START_BP(VERIFY_line_61);
-    // PAPER LINE 61
     sc_mulsub(m_y0.bytes, proof.taux.bytes, weight_y.bytes, m_y0.bytes);
 
     const rct::keyV zpow = vector_powers(pd.z, M+3);
@@ -962,7 +959,6 @@ bool bulletproof_VERIFY(const std::vector<const Bulletproof*> &proofs)
     PERF_TIMER_STOP_BP(VERIFY_line_61rl_new);
 
     PERF_TIMER_START_BP(VERIFY_line_62);
-    // PAPER LINE 62
     multiexp_data.emplace_back(weight_z, proof8_A);
     sc_mul(tmp.bytes, pd.x.bytes, weight_z.bytes);
     multiexp_data.emplace_back(tmp, proof8_S);
@@ -973,7 +969,6 @@ bool bulletproof_VERIFY(const std::vector<const Bulletproof*> &proofs)
     CHECK_AND_ASSERT_MES(rounds > 0, false, "Zero rounds");
 
     PERF_TIMER_START_BP(VERIFY_line_24_25);
-    // Basically PAPER LINES 24-25
     // Compute the curvepoints from G[i] and H[i]
     rct::key yinvpow = rct::identity();
     rct::key ypow = rct::identity();
@@ -1010,7 +1005,6 @@ bool bulletproof_VERIFY(const std::vector<const Bulletproof*> &proofs)
       sc_mul(g_scalar.bytes, g_scalar.bytes, w_cache[i].bytes);
       sc_mul(h_scalar.bytes, h_scalar.bytes, w_cache[(~i) & (MN-1)].bytes);
 
-      // Adjust the scalars using the exponents from PAPER LINE 62
       sc_add(g_scalar.bytes, g_scalar.bytes, pd.z.bytes);
       CHECK_AND_ASSERT_MES(2+i/N < zpow.size(), false, "invalid zpow index");
       CHECK_AND_ASSERT_MES(i%N < twoN.size(), false, "invalid twoN index");
@@ -1043,7 +1037,6 @@ bool bulletproof_VERIFY(const std::vector<const Bulletproof*> &proofs)
 
     PERF_TIMER_STOP_BP(VERIFY_line_24_25);
 
-    // PAPER LINE 26
     PERF_TIMER_START_BP(VERIFY_line_26_new);
     sc_muladd(z1.bytes, proof.mu.bytes, weight_z.bytes, z1.bytes);
     for (size_t i = 0; i < rounds; ++i)