Auto merge of #1919 - ebfull:abstract-verification, r=str4d

Isolate verification to a ProofVerifier context object that allows verification behavior to be tuned by the caller.

This is an alternative foundation for #1892, i.e., #1892 will have to be changed if this PR is accepted.

I think this is a safer approach because it allows us to isolate verification behavior to a single object. This will come in handy when @arielgabizon finishes the batching code.

src/gtest/test_joinsplit.cpp

@@ -15,6 +15,9 @@ using namespace libzcash;
 
 void test_full_api(ZCJoinSplit* js)
 {
+    // Create verification context.
+    auto verifier = libzcash::ProofVerifier::Strict();
+
     // The recipient's information.
     SpendingKey recipient_key = SpendingKey::random();
     PaymentAddress recipient_addr = recipient_key.address();
@@ -69,6 +72,7 @@ void test_full_api(ZCJoinSplit* js)
     // Verify the transaction:
     ASSERT_TRUE(js->verify(
         proof,
+        verifier,
         pubKeyHash,
         randomSeed,
         macs,
@@ -143,6 +147,7 @@ void test_full_api(ZCJoinSplit* js)
     // Verify the transaction:
     ASSERT_TRUE(js->verify(
         proof,
+        verifier,
         pubKeyHash,
         randomSeed,
         macs,

src/gtest/test_proofs.cpp

@@ -336,6 +336,29 @@ TEST(proofs, zksnark_serializes_properly)
     auto example = libsnark::generate_r1cs_example_with_field_input<curve_Fr>(250, 4);
     example.constraint_system.swap_AB_if_beneficial();
     auto kp = libsnark::r1cs_ppzksnark_generator<curve_pp>(example.constraint_system);
+    auto vkprecomp = libsnark::r1cs_ppzksnark_verifier_process_vk(kp.vk);
+
+    for (size_t i = 0; i < 20; i++) {
+        auto badproof = ZCProof::random_invalid();
+        auto proof = badproof.to_libsnark_proof<libsnark::r1cs_ppzksnark_proof<curve_pp>>();
+        
+        auto verifierEnabled = ProofVerifier::Strict();
+        auto verifierDisabled = ProofVerifier::Disabled();
+        // This verifier should catch the bad proof
+        ASSERT_FALSE(verifierEnabled.check(
+            kp.vk,
+            vkprecomp,
+            example.primary_input,
+            proof
+        ));
+        // This verifier won't!
+        ASSERT_TRUE(verifierDisabled.check(
+            kp.vk,
+            vkprecomp,
+            example.primary_input,
+            proof
+        ));
+    }
 
     for (size_t i = 0; i < 20; i++) {
         auto proof = libsnark::r1cs_ppzksnark_prover<curve_pp>(
@@ -345,6 +368,23 @@ TEST(proofs, zksnark_serializes_properly)
             example.constraint_system
         );
 
+        {
+            auto verifierEnabled = ProofVerifier::Strict();
+            auto verifierDisabled = ProofVerifier::Disabled();
+            ASSERT_TRUE(verifierEnabled.check(
+                kp.vk,
+                vkprecomp,
+                example.primary_input,
+                proof
+            ));
+            ASSERT_TRUE(verifierDisabled.check(
+                kp.vk,
+                vkprecomp,
+                example.primary_input,
+                proof
+            ));
+        }
+
         ASSERT_TRUE(libsnark::r1cs_ppzksnark_verifier_strong_IC<curve_pp>(
             kp.vk,
             example.primary_input,