4 files changed, 71 insertions, 12 deletions
diff --git a/src/Makefile.bench.include b/src/Makefile.bench.include
index 766c0fca54..93b5156af3 100644
--- a/src/Makefile.bench.include
+++ b/src/Makefile.bench.include
@@ -29,6 +29,7 @@ bench_bench_bitcoin_SOURCES = \
   bench/crypto_hash.cpp \
   bench/ccoins_caching.cpp \
   bench/gcs_filter.cpp \
+  bench/hashpadding.cpp \
   bench/merkle_root.cpp \
   bench/mempool_eviction.cpp \
   bench/mempool_stress.cpp \
diff --git a/src/bench/hashpadding.cpp b/src/bench/hashpadding.cpp
new file mode 100644
index 0000000000..985be8bdba
--- /dev/null
+++ b/src/bench/hashpadding.cpp
@@ -0,0 +1,47 @@
+// Copyright (c) 2015-2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <bench/bench.h>
+#include <hash.h>
+#include <random.h>
+#include <uint256.h>
+
+
+static void PrePadded(benchmark::State& state)
+{
+
+    CSHA256 hasher;
+
+    // Setup the salted hasher
+    uint256 nonce = GetRandHash();
+    hasher.Write(nonce.begin(), 32);
+    hasher.Write(nonce.begin(), 32);
+    uint256 data = GetRandHash();
+    while (state.KeepRunning()) {
+        unsigned char out[32];
+        CSHA256 h = hasher;
+        h.Write(data.begin(), 32);
+        h.Finalize(out);
+    }
+}
+
+BENCHMARK(PrePadded, 10000);
+
+static void RegularPadded(benchmark::State& state)
+{
+    CSHA256 hasher;
+
+    // Setup the salted hasher
+    uint256 nonce = GetRandHash();
+    uint256 data = GetRandHash();
+    while (state.KeepRunning()) {
+        unsigned char out[32];
+        CSHA256 h = hasher;
+        h.Write(nonce.begin(), 32);
+        h.Write(data.begin(), 32);
+        h.Finalize(out);
+    }
+}
+
+BENCHMARK(RegularPadded, 10000);
diff --git a/src/script/sigcache.cpp b/src/script/sigcache.cpp
index e7b6df3ce8..3c54d5bee4 100644
--- a/src/script/sigcache.cpp
+++ b/src/script/sigcache.cpp
@@ -23,7 +23,7 @@ class CSignatureCache
 {
 private:
      //! Entries are SHA256(nonce || signature hash || public key || signature):
-    uint256 nonce;
+    CSHA256 m_salted_hasher;
     typedef CuckooCache::cache<uint256, SignatureCacheHasher> map_type;
     map_type setValid;
     boost::shared_mutex cs_sigcache;
@@ -31,13 +31,19 @@ private:
 public:
     CSignatureCache()
     {
-        GetRandBytes(nonce.begin(), 32);
+        uint256 nonce = GetRandHash();
+        // We want the nonce to be 64 bytes long to force the hasher to process
+        // this chunk, which makes later hash computations more efficient. We
+        // just write our 32-byte entropy twice to fill the 64 bytes.
+        m_salted_hasher.Write(nonce.begin(), 32);
+        m_salted_hasher.Write(nonce.begin(), 32);
     }
 
     void
     ComputeEntry(uint256& entry, const uint256 &hash, const std::vector<unsigned char>& vchSig, const CPubKey& pubkey)
     {
-        CSHA256().Write(nonce.begin(), 32).Write(hash.begin(), 32).Write(&pubkey[0], pubkey.size()).Write(&vchSig[0], vchSig.size()).Finalize(entry.begin());
+        CSHA256 hasher = m_salted_hasher;
+        hasher.Write(hash.begin(), 32).Write(&pubkey[0], pubkey.size()).Write(&vchSig[0], vchSig.size()).Finalize(entry.begin());
     }
 
     bool
diff --git a/src/validation.cpp b/src/validation.cpp
index 396fc0a1b5..0d57900670 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1481,14 +1481,21 @@ int GetSpendHeight(const CCoinsViewCache& inputs)
 }
 
 
-static CuckooCache::cache<uint256, SignatureCacheHasher> scriptExecutionCache;
-static uint256 scriptExecutionCacheNonce(GetRandHash());
+static CuckooCache::cache<uint256, SignatureCacheHasher> g_scriptExecutionCache;
+static CSHA256 g_scriptExecutionCacheHasher;
 
 void InitScriptExecutionCache() {
+    // Setup the salted hasher
+    uint256 nonce = GetRandHash();
+    // We want the nonce to be 64 bytes long to force the hasher to process
+    // this chunk, which makes later hash computations more efficient. We
+    // just write our 32-byte entropy twice to fill the 64 bytes.
+    g_scriptExecutionCacheHasher.Write(nonce.begin(), 32);
+    g_scriptExecutionCacheHasher.Write(nonce.begin(), 32);
     // nMaxCacheSize is unsigned. If -maxsigcachesize is set to zero,
     // setup_bytes creates the minimum possible cache (2 elements).
     size_t nMaxCacheSize = std::min(std::max((int64_t)0, gArgs.GetArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) / 2), MAX_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);
-    size_t nElems = scriptExecutionCache.setup_bytes(nMaxCacheSize);
+    size_t nElems = g_scriptExecutionCache.setup_bytes(nMaxCacheSize);
     LogPrintf("Using %zu MiB out of %zu/2 requested for script execution cache, able to store %zu elements\n",
             (nElems*sizeof(uint256)) >>20, (nMaxCacheSize*2)>>20, nElems);
 }
@@ -1526,12 +1533,10 @@ bool CheckInputScripts(const CTransaction& tx, TxValidationState &state, const C
     // properly commits to the scriptPubKey in the inputs view of that
     // transaction).
     uint256 hashCacheEntry;
-    // We only use the first 19 bytes of nonce to avoid a second SHA
-    // round - giving us 19 + 32 + 4 = 55 bytes (+ 8 + 1 = 64)
-    static_assert(55 - sizeof(flags) - 32 >= 128/8, "Want at least 128 bits of nonce for script execution cache");
-    CSHA256().Write(scriptExecutionCacheNonce.begin(), 55 - sizeof(flags) - 32).Write(tx.GetWitnessHash().begin(), 32).Write((unsigned char*)&flags, sizeof(flags)).Finalize(hashCacheEntry.begin());
+    CSHA256 hasher = g_scriptExecutionCacheHasher;
+    hasher.Write(tx.GetWitnessHash().begin(), 32).Write((unsigned char*)&flags, sizeof(flags)).Finalize(hashCacheEntry.begin());
     AssertLockHeld(cs_main); //TODO: Remove this requirement by making CuckooCache not require external locks
-    if (scriptExecutionCache.contains(hashCacheEntry, !cacheFullScriptStore)) {
+    if (g_scriptExecutionCache.contains(hashCacheEntry, !cacheFullScriptStore)) {
         return true;
     }
 
@@ -1586,7 +1591,7 @@ bool CheckInputScripts(const CTransaction& tx, TxValidationState &state, const C
     if (cacheFullScriptStore && !pvChecks) {
         // We executed all of the provided scripts, and were told to
         // cache the result. Do so now.
-        scriptExecutionCache.insert(hashCacheEntry);
+        g_scriptExecutionCache.insert(hashCacheEntry);
     }
 
     return true;