Add encoding and decoding for Sapling extended full viewing keys

src/chainparams.cpp

@@ -171,6 +171,7 @@ public:
         bech32HRPs[SAPLING_FULL_VIEWING_KEY]     = "zviews";
         bech32HRPs[SAPLING_INCOMING_VIEWING_KEY] = "zivks";
         bech32HRPs[SAPLING_EXTENDED_SPEND_KEY]   = "secret-extended-key-main";
+        bech32HRPs[SAPLING_EXTENDED_FVK]         = "zxviews";
 
         vFixedSeeds = std::vector<SeedSpec6>(pnSeed6_main, pnSeed6_main + ARRAYLEN(pnSeed6_main));
 
@@ -384,6 +385,7 @@ public:
         bech32HRPs[SAPLING_FULL_VIEWING_KEY]     = "zviewtestsapling";
         bech32HRPs[SAPLING_INCOMING_VIEWING_KEY] = "zivktestsapling";
         bech32HRPs[SAPLING_EXTENDED_SPEND_KEY]   = "secret-extended-key-test";
+        bech32HRPs[SAPLING_EXTENDED_FVK]         = "zxviewtestsapling";
 
         vFixedSeeds = std::vector<SeedSpec6>(pnSeed6_test, pnSeed6_test + ARRAYLEN(pnSeed6_test));
 
@@ -529,6 +531,7 @@ public:
         bech32HRPs[SAPLING_FULL_VIEWING_KEY]     = "zviewregtestsapling";
         bech32HRPs[SAPLING_INCOMING_VIEWING_KEY] = "zivkregtestsapling";
         bech32HRPs[SAPLING_EXTENDED_SPEND_KEY]   = "secret-extended-key-regtest";
+        bech32HRPs[SAPLING_EXTENDED_FVK]         = "zxviewregtestsapling";
 
         // Founders reward script expects a vector of 2-of-3 multisig addresses
         vFoundersRewardAddress = { "t2FwcEhFdNXuFMv1tcYwaBJtYVtMj8b1uTg" };

src/chainparams.h

@@ -61,6 +61,7 @@ public:
         SAPLING_FULL_VIEWING_KEY,
         SAPLING_INCOMING_VIEWING_KEY,
         SAPLING_EXTENDED_SPEND_KEY,
+        SAPLING_EXTENDED_FVK,
 
         MAX_BECH32_TYPES
     };

src/gtest/test_keys.cpp

@@ -27,6 +27,20 @@ TEST(Keys, EncodeAndDecodeSapling)
             auto sk2 = boost::get<libzcash::SaplingExtendedSpendingKey>(spendingkey2);
             EXPECT_EQ(sk, sk2);
         }
+        {
+            auto extfvk = sk.ToXFVK();
+            std::string vk_string = EncodeViewingKey(extfvk);
+            EXPECT_EQ(
+                vk_string.substr(0, 7),
+                Params().Bech32HRP(CChainParams::SAPLING_EXTENDED_FVK));
+
+            auto viewingkey2 = DecodeViewingKey(vk_string);
+            EXPECT_TRUE(IsValidViewingKey(viewingkey2));
+
+            ASSERT_TRUE(boost::get<libzcash::SaplingExtendedFullViewingKey>(&viewingkey2) != nullptr);
+            auto extfvk2 = boost::get<libzcash::SaplingExtendedFullViewingKey>(viewingkey2);
+            EXPECT_EQ(extfvk, extfvk2);
+        }
         {
             auto addr = sk.DefaultAddress();
 

src/key_io.cpp

@@ -120,6 +120,22 @@ public:
         return ret;
     }
 
+    std::string operator()(const libzcash::SaplingExtendedFullViewingKey& extfvk) const
+    {
+        CDataStream ss(SER_NETWORK, PROTOCOL_VERSION);
+        ss << extfvk;
+        // ConvertBits requires unsigned char, but CDataStream uses char
+        std::vector<unsigned char> serkey(ss.begin(), ss.end());
+        std::vector<unsigned char> data;
+        // See calculation comment below
+        data.reserve((serkey.size() * 8 + 4) / 5);
+        ConvertBits<8, 5, true>([&](unsigned char c) { data.push_back(c); }, serkey.begin(), serkey.end());
+        std::string ret = bech32::Encode(m_params.Bech32HRP(CChainParams::SAPLING_EXTENDED_FVK), data);
+        memory_cleanse(serkey.data(), serkey.size());
+        memory_cleanse(data.data(), data.size());
+        return ret;
+    }
+
     std::string operator()(const libzcash::InvalidEncoding& no) const { return {}; }
 };
 
@@ -161,11 +177,12 @@ public:
     std::string operator()(const libzcash::InvalidEncoding& no) const { return {}; }
 };
 
-// Sizes of SaplingPaymentAddress and SaplingSpendingKey after
-// ConvertBits<8, 5, true>(). The calculations below take the
-// regular serialized size in bytes, convert to bits, and then
+// Sizes of SaplingPaymentAddress, SaplingExtendedFullViewingKey, and
+// SaplingExtendedSpendingKey after ConvertBits<8, 5, true>(). The calculations
+// below take the regular serialized size in bytes, convert to bits, and then
 // perform ceiling division to get the number of 5-bit clusters.
 const size_t ConvertedSaplingPaymentAddressSize = ((32 + 11) * 8 + 4) / 5;
+const size_t ConvertedSaplingExtendedFullViewingKeySize = (ZIP32_XFVK_SIZE * 8 + 4) / 5;
 const size_t ConvertedSaplingExtendedSpendingKeySize = (ZIP32_XSK_SIZE * 8 + 4) / 5;
 } // namespace
 
@@ -270,11 +287,11 @@ std::string EncodePaymentAddress(const libzcash::PaymentAddress& zaddr)
     return boost::apply_visitor(PaymentAddressEncoder(Params()), zaddr);
 }
 
-template<typename T1, typename T2, typename T3 = T2>
+template<typename T1, typename T2, typename T3>
 T1 DecodeAny(
     const std::string& str,
     std::pair<CChainParams::Base58Type, size_t> sprout,
-    boost::optional<std::pair<CChainParams::Bech32Type, size_t>> sapling)
+    std::pair<CChainParams::Bech32Type, size_t> sapling)
 {
     std::vector<unsigned char> data;
     if (DecodeBase58Check(str, data)) {
@@ -291,20 +308,18 @@ T1 DecodeAny(
         }
     }
 
-    if (sapling) {
-        data.clear();
-        auto bech = bech32::Decode(str);
-        if (bech.first == Params().Bech32HRP(sapling.get().first) &&
-            bech.second.size() == sapling.get().second) {
-            // Bech32 decoding
-            data.reserve((bech.second.size() * 5) / 8);
-            if (ConvertBits<5, 8, false>([&](unsigned char c) { data.push_back(c); }, bech.second.begin(), bech.second.end())) {
-                CDataStream ss(data, SER_NETWORK, PROTOCOL_VERSION);
-                T3 ret;
-                ss >> ret;
-                memory_cleanse(data.data(), data.size());
-                return ret;
-            }
+    data.clear();
+    auto bech = bech32::Decode(str);
+    if (bech.first == Params().Bech32HRP(sapling.first) &&
+        bech.second.size() == sapling.second) {
+        // Bech32 decoding
+        data.reserve((bech.second.size() * 5) / 8);
+        if (ConvertBits<5, 8, false>([&](unsigned char c) { data.push_back(c); }, bech.second.begin(), bech.second.end())) {
+            CDataStream ss(data, SER_NETWORK, PROTOCOL_VERSION);
+            T3 ret;
+            ss >> ret;
+            memory_cleanse(data.data(), data.size());
+            return ret;
         }
     }
 
@@ -335,10 +350,11 @@ std::string EncodeViewingKey(const libzcash::ViewingKey& vk)
 libzcash::ViewingKey DecodeViewingKey(const std::string& str)
 {
     return DecodeAny<libzcash::ViewingKey,
-        libzcash::SproutViewingKey>(
+        libzcash::SproutViewingKey,
+        libzcash::SaplingExtendedFullViewingKey>(
             str,
             std::make_pair(CChainParams::ZCVIEWING_KEY, libzcash::SerializedSproutViewingKeySize),
-            boost::none
+            std::make_pair(CChainParams::SAPLING_EXTENDED_FVK, ConvertedSaplingExtendedFullViewingKeySize)
         );
 }
 

src/zcash/Address.hpp

@@ -15,7 +15,7 @@ public:
 };
 
 typedef boost::variant<InvalidEncoding, SproutPaymentAddress, SaplingPaymentAddress> PaymentAddress;
-typedef boost::variant<InvalidEncoding, SproutViewingKey> ViewingKey;
+typedef boost::variant<InvalidEncoding, SproutViewingKey, SaplingExtendedFullViewingKey> ViewingKey;
 typedef boost::variant<InvalidEncoding, SproutSpendingKey, SaplingExtendedSpendingKey> SpendingKey;
 
 class AddressInfoFromSpendingKey : public boost::static_visitor<std::pair<std::string, PaymentAddress>> {