Add optional bool to disable computation of proof in JSDescription constructor

src/primitives/transaction.cpp

@@ -15,11 +15,14 @@ JSDescription::JSDescription(ZCJoinSplit& params,
             const boost::array<libzcash::JSInput, ZC_NUM_JS_INPUTS>& inputs,
             const boost::array<libzcash::JSOutput, ZC_NUM_JS_OUTPUTS>& outputs,
             CAmount vpub_old,
-            CAmount vpub_new) : vpub_old(vpub_old), vpub_new(vpub_new), anchor(anchor)
+            CAmount vpub_new,
+            bool computeProof) : vpub_old(vpub_old), vpub_new(vpub_new), anchor(anchor)
 {
     boost::array<libzcash::Note, ZC_NUM_JS_OUTPUTS> notes;
 
-    params.loadProvingKey();
+    if (computeProof) {
+        params.loadProvingKey();
+    }
     proof = params.prove(
         inputs,
         outputs,
@@ -33,7 +36,8 @@ JSDescription::JSDescription(ZCJoinSplit& params,
         commitments,
         vpub_old,
         vpub_new,
-        anchor
+        anchor,
+        computeProof
     );
 }
 

src/primitives/transaction.h

@@ -74,7 +74,8 @@ public:
             const boost::array<libzcash::JSInput, ZC_NUM_JS_INPUTS>& inputs,
             const boost::array<libzcash::JSOutput, ZC_NUM_JS_OUTPUTS>& outputs,
             CAmount vpub_old,
-            CAmount vpub_new
+            CAmount vpub_new,
+            bool computeProof = true // Set to false in some tests
     );
 
     // Verifies that the JoinSplit proof is correct.

src/zcash/JoinSplit.cpp

@@ -173,9 +173,10 @@ public:
         boost::array<uint256, NumOutputs>& out_commitments,
         uint64_t vpub_old,
         uint64_t vpub_new,
-        const uint256& rt
+        const uint256& rt,
+        bool computeProof
     ) {
-        if (!pk) {
+        if (computeProof && !pk) {
             throw std::runtime_error("JoinSplit proving key not loaded");
         }
 
@@ -231,6 +232,10 @@ public:
             out_macs[i] = PRF_pk(inputs[i].key, i, h_sig);
         }
 
+        if (!computeProof) {
+            return ZCProof();
+        }
+
         protoboard<FieldT> pb;
         {
             joinsplit_gadget<FieldT, NumInputs, NumOutputs> g(pb);

src/zcash/JoinSplit.hpp

@@ -73,7 +73,8 @@ public:
         boost::array<uint256, NumOutputs>& out_commitments,
         uint64_t vpub_old,
         uint64_t vpub_new,
-        const uint256& rt
+        const uint256& rt,
+        bool computeProof = true
     ) = 0;
 
     virtual bool verify(