Merge #19601: Refactoring CHashWriter & Get{Prevouts,Sequence,Outputs}Hash to SHA256 (Alternative to #18071)

9ab4cafabda227ccee5b241d7690fc67f9a27221 Refactor Get{Prevout,Sequence,Outputs}Hash to Get{Prevouts,Sequences,Outputs}SHA256. (Jeremy Rubin)
6510d0ff4173a7b01d6728051303c7c38eb34533 Add SHA256Uint256 helper functions (Jeremy Rubin)
b475d7d0fa000d5802caf3065b8b2abcea60719b Add single sha256 call to CHashWriter (Jeremy Rubin)

Pull request description:

  Opened as an alternative to #18071 to be more similar to #17977.

  I'm fine with either, deferring to others.

  cc jnewbery Sjors

ACKs for top commit:
  jnewbery:
    Code review ACK 9ab4cafabda227ccee5b241d7690fc67f9a27221
  jonatack:
    Tested ACK 9ab4caf
  fjahr:
    tested ACK 9ab4cafabda227ccee5b241d7690fc67f9a27221
  instagibbs:
    reACK https://github.com/bitcoin/bitcoin/pull/19601/commits/9ab4cafabda227ccee5b241d7690fc67f9a27221

Tree-SHA512: 93a7a47697f1657f027b18407bdcce16963f6b23d12372e7ac8fd4ee96769b3e2639369f9956fee669cc881b6338641cddfeeef1516c7104cb50ef4b880bb0a7

3 files changed, 46 insertions, 19 deletions

diff --git a/src/hash.cpp b/src/hash.cpp
index 4c09f5f646..83b90ae063 100644
--- a/src/hash.cpp
+++ b/src/hash.cpp
@@ -77,3 +77,10 @@ void BIP32Hash(const ChainCode &chainCode, unsigned int nChild, unsigned char he
     num[3] = (nChild >>  0) & 0xFF;
     CHMAC_SHA512(chainCode.begin(), chainCode.size()).Write(&header, 1).Write(data, 32).Write(num, 4).Finalize(output);
 }
+
+uint256 SHA256Uint256(const uint256& input)
+{
+    uint256 result;
+    CSHA256().Write(input.begin(), 32).Finalize(result.begin());
+    return result;
+}
diff --git a/src/hash.h b/src/hash.h
index 71806483ff..c16bbb48ce 100644
--- a/src/hash.h
+++ b/src/hash.h
@@ -6,6 +6,7 @@
 #ifndef BITCOIN_HASH_H
 #define BITCOIN_HASH_H
 
+#include <attributes.h>
 #include <crypto/common.h>
 #include <crypto/ripemd160.h>
 #include <crypto/sha256.h>
@@ -98,7 +99,7 @@ inline uint160 Hash160(const T1& in1)
 class CHashWriter
 {
 private:
-    CHash256 ctx;
+    CSHA256 ctx;
 
     const int nType;
     const int nVersion;
@@ -110,13 +111,27 @@ public:
     int GetVersion() const { return nVersion; }
 
     void write(const char *pch, size_t size) {
-        ctx.Write({(const unsigned char*)pch, size});
+        ctx.Write((const unsigned char*)pch, size);
     }
 
-    // invalidates the object
+    /** Compute the double-SHA256 hash of all data written to this object.
+     *
+     * Invalidates this object.
+     */
     uint256 GetHash() {
         uint256 result;
-        ctx.Finalize(result);
+        ctx.Finalize(result.begin());
+        ctx.Reset().Write(result.begin(), CSHA256::OUTPUT_SIZE).Finalize(result.begin());
+        return result;
+    }
+
+    /** Compute the SHA256 hash of all data written to this object.
+     *
+     * Invalidates this object.
+     */
+    uint256 GetSHA256() {
+        uint256 result;
+        ctx.Finalize(result.begin());
         return result;
     }
 
@@ -124,9 +139,8 @@ public:
      * Returns the first 64 bits from the resulting hash.
      */
     inline uint64_t GetCheapHash() {
-        unsigned char result[CHash256::OUTPUT_SIZE];
-        ctx.Finalize(result);
-        return ReadLE64(result);
+        uint256 result = GetHash();
+        return ReadLE64(result.begin());
     }
 
     template<typename T>
@@ -181,6 +195,9 @@ uint256 SerializeHash(const T& obj, int nType=SER_GETHASH, int nVersion=PROTOCOL
     return ss.GetHash();
 }
 
+/** Single-SHA256 a 32-byte input (represented as uint256). */
+NODISCARD uint256 SHA256Uint256(const uint256& input);
+
 unsigned int MurmurHash3(unsigned int nHashSeed, Span<const unsigned char> vDataToHash);
 
 void BIP32Hash(const ChainCode &chainCode, unsigned int nChild, unsigned char header, const unsigned char data[32], unsigned char output[64]);
diff --git a/src/script/interpreter.cpp b/src/script/interpreter.cpp
index 39feb4ccc9..7b2457a5e3 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];