From 9ab4cafabda227ccee5b241d7690fc67f9a27221 Mon Sep 17 00:00:00 2001
From: Jeremy Rubin <j@rubin.io>
Date: Wed, 5 Feb 2020 12:31:20 -0800
Subject: [PATCH] Refactor Get{Prevout,Sequence,Outputs}Hash to
 Get{Prevouts,Sequences,Outputs}SHA256.

Several proposals (Taproot, MuHash, CTV) require access to the single
hash.
---
 src/script/interpreter.cpp | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/src/script/interpreter.cpp b/src/script/interpreter.cpp
index 39feb4ccc92..7b2457a5e39 100644
--- a/src/script/interpreter.cpp
+++ b/src/script/interpreter.cpp
@@ -1258,34 +1258,37 @@ public:
     }
 };
 
+/** Compute the (single) SHA256 of the concatenation of all prevouts of a tx. */
 template <class T>
-uint256 GetPrevoutHash(const T& txTo)
+uint256 GetPrevoutsSHA256(const T& txTo)
 {
     CHashWriter ss(SER_GETHASH, 0);
     for (const auto& txin : txTo.vin) {
         ss << txin.prevout;
     }
-    return ss.GetHash();
+    return ss.GetSHA256();
 }
 
+/** Compute the (single) SHA256 of the concatenation of all nSequences of a tx. */
 template <class T>
-uint256 GetSequenceHash(const T& txTo)
+uint256 GetSequencesSHA256(const T& txTo)
 {
     CHashWriter ss(SER_GETHASH, 0);
     for (const auto& txin : txTo.vin) {
         ss << txin.nSequence;
     }
-    return ss.GetHash();
+    return ss.GetSHA256();
 }
 
+/** Compute the (single) SHA256 of the concatenation of all txouts of a tx. */
 template <class T>
-uint256 GetOutputsHash(const T& txTo)
+uint256 GetOutputsSHA256(const T& txTo)
 {
     CHashWriter ss(SER_GETHASH, 0);
     for (const auto& txout : txTo.vout) {
         ss << txout;
     }
-    return ss.GetHash();
+    return ss.GetSHA256();
 }
 
 } // namespace
@@ -1297,9 +1300,9 @@ void PrecomputedTransactionData::Init(const T& txTo)
 
     // Cache is calculated only for transactions with witness
     if (txTo.HasWitness()) {
-        hashPrevouts = GetPrevoutHash(txTo);
-        hashSequence = GetSequenceHash(txTo);
-        hashOutputs = GetOutputsHash(txTo);
+        hashPrevouts = SHA256Uint256(GetPrevoutsSHA256(txTo));
+        hashSequence = SHA256Uint256(GetSequencesSHA256(txTo));
+        hashOutputs = SHA256Uint256(GetOutputsSHA256(txTo));
     }
 
     m_ready = true;
@@ -1329,16 +1332,16 @@ uint256 SignatureHash(const CScript& scriptCode, const T& txTo, unsigned int nIn
         const bool cacheready = cache && cache->m_ready;
 
         if (!(nHashType & SIGHASH_ANYONECANPAY)) {
-            hashPrevouts = cacheready ? cache->hashPrevouts : GetPrevoutHash(txTo);
+            hashPrevouts = cacheready ? cache->hashPrevouts : SHA256Uint256(GetPrevoutsSHA256(txTo));
         }
 
         if (!(nHashType & SIGHASH_ANYONECANPAY) && (nHashType & 0x1f) != SIGHASH_SINGLE && (nHashType & 0x1f) != SIGHASH_NONE) {
-            hashSequence = cacheready ? cache->hashSequence : GetSequenceHash(txTo);
+            hashSequence = cacheready ? cache->hashSequence : SHA256Uint256(GetSequencesSHA256(txTo));
         }
 
 
         if ((nHashType & 0x1f) != SIGHASH_SINGLE && (nHashType & 0x1f) != SIGHASH_NONE) {
-            hashOutputs = cacheready ? cache->hashOutputs : GetOutputsHash(txTo);
+            hashOutputs = cacheready ? cache->hashOutputs : SHA256Uint256(GetOutputsSHA256(txTo));
         } else if ((nHashType & 0x1f) == SIGHASH_SINGLE && nIn < txTo.vout.size()) {
             CHashWriter ss(SER_GETHASH, 0);
             ss << txTo.vout[nIn];