From 7f0aa74666acf962bc37dca21339bb438a2195b1 Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@z.cash>
Date: Tue, 18 Oct 2016 00:22:58 -0500
Subject: [PATCH] Implement static method for creating a randomized
 JSDescription

---
 src/primitives/transaction.cpp | 24 ++++++++++++++++++++++++
 src/primitives/transaction.h   | 13 +++++++++++++
 src/test/transaction_tests.cpp | 26 ++++++++++++++++++++++++++
 3 files changed, 63 insertions(+)

diff --git a/src/primitives/transaction.cpp b/src/primitives/transaction.cpp
index 1cedd6f27..704b10a5c 100644
--- a/src/primitives/transaction.cpp
+++ b/src/primitives/transaction.cpp
@@ -6,6 +6,7 @@
 #include "primitives/transaction.h"
 
 #include "hash.h"
+#include "random.h"
 #include "tinyformat.h"
 #include "utilstrencodings.h"
 
@@ -41,6 +42,29 @@ JSDescription::JSDescription(ZCJoinSplit& params,
     );
 }
 
+JSDescription JSDescription::Randomized(
+            ZCJoinSplit& params,
+            const uint256& pubKeyHash,
+            const uint256& anchor,
+            boost::array<libzcash::JSInput, ZC_NUM_JS_INPUTS>& inputs,
+            boost::array<libzcash::JSOutput, ZC_NUM_JS_OUTPUTS>& outputs,
+            boost::array<size_t, ZC_NUM_JS_INPUTS>& inputMap,
+            boost::array<size_t, ZC_NUM_JS_OUTPUTS>& outputMap,
+            CAmount vpub_old,
+            CAmount vpub_new,
+            bool computeProof)
+{
+    // Randomize the order of the inputs and outputs
+    inputMap = {0, 1};
+    outputMap = {0, 1};
+    MappedShuffle(inputs.begin(), inputMap.begin(), ZC_NUM_JS_INPUTS, GetRandInt);
+    MappedShuffle(outputs.begin(), outputMap.begin(), ZC_NUM_JS_OUTPUTS, GetRandInt);
+
+    return JSDescription(
+        params, pubKeyHash, anchor, inputs, outputs,
+        vpub_old, vpub_new, computeProof);
+}
+
 bool JSDescription::Verify(
     ZCJoinSplit& params,
     const uint256& pubKeyHash
diff --git a/src/primitives/transaction.h b/src/primitives/transaction.h
index 2e83773c4..b665033d8 100644
--- a/src/primitives/transaction.h
+++ b/src/primitives/transaction.h
@@ -78,6 +78,19 @@ public:
             bool computeProof = true // Set to false in some tests
     );
 
+    static JSDescription Randomized(
+            ZCJoinSplit& params,
+            const uint256& pubKeyHash,
+            const uint256& rt,
+            boost::array<libzcash::JSInput, ZC_NUM_JS_INPUTS>& inputs,
+            boost::array<libzcash::JSOutput, ZC_NUM_JS_OUTPUTS>& outputs,
+            boost::array<size_t, ZC_NUM_JS_INPUTS>& inputMap,
+            boost::array<size_t, ZC_NUM_JS_OUTPUTS>& outputMap,
+            CAmount vpub_old,
+            CAmount vpub_new,
+            bool computeProof = true // Set to false in some tests
+    );
+
     // Verifies that the JoinSplit proof is correct.
     bool Verify(ZCJoinSplit& params, const uint256& pubKeyHash) const;
 
diff --git a/src/test/transaction_tests.cpp b/src/test/transaction_tests.cpp
index c2b0a7017..e7a932a4f 100644
--- a/src/test/transaction_tests.cpp
+++ b/src/test/transaction_tests.cpp
@@ -368,6 +368,32 @@ BOOST_AUTO_TEST_CASE(test_basic_joinsplit_verification)
         BOOST_CHECK(!test.Verify(*p, pubKeyHash));
     }
 
+    {
+        boost::array<size_t, ZC_NUM_JS_INPUTS> inputMap;
+        boost::array<size_t, ZC_NUM_JS_OUTPUTS> outputMap;
+        auto jsdesc = JSDescription::Randomized(
+            *p, pubKeyHash, rt,
+            inputs, outputs,
+            inputMap, outputMap,
+            0, 0);
+        BOOST_CHECK(jsdesc.Verify(*p, pubKeyHash));
+
+        std::set<size_t> inputSet;
+        for (size_t i = 0; i < ZC_NUM_JS_INPUTS; i++) {
+            inputSet.insert(inputMap[i]);
+        }
+        std::set<size_t> expectedInputSet {0, 1};
+        BOOST_CHECK(expectedInputSet == inputSet);
+
+        std::set<size_t> outputSet;
+        for (size_t i = 0; i < ZC_NUM_JS_OUTPUTS; i++) {
+            outputSet.insert(outputMap[i]);
+        }
+        std::set<size_t> expectedOutputSet {0, 1};
+        BOOST_CHECK(expectedOutputSet == outputSet);
+    }
+
+
     delete p;
 }