From cd4e553914222802b3b28e37e9f3df199efb3880 Mon Sep 17 00:00:00 2001
From: Gregory Sanders <gsanders87@gmail.com>
Date: Tue, 11 Dec 2018 11:24:36 -0500
Subject: [PATCH] CProof (re)setting and validation helper functions

---
 src/Makefile.am     |  2 ++
 src/block_proof.cpp | 62 +++++++++++++++++++++++++++++++++++++++++++++
 src/block_proof.h   | 26 +++++++++++++++++++
 3 files changed, 90 insertions(+)
 create mode 100644 src/block_proof.cpp
 create mode 100644 src/block_proof.h

diff --git a/src/Makefile.am b/src/Makefile.am
index 81700addf3..16d31b8efc 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -96,6 +96,7 @@ BITCOIN_CORE_H = \
   bech32.h \
   bloom.h \
   blockencodings.h \
+  block_proof.h \
   chain.h \
   chainparams.h \
   chainparamsbase.h \
@@ -221,6 +222,7 @@ libbitcoin_server_a_SOURCES = \
   addrman.cpp \
   bloom.cpp \
   blockencodings.cpp \
+  block_proof.cpp \
   chain.cpp \
   checkpoints.cpp \
   consensus/tx_verify.cpp \
diff --git a/src/block_proof.cpp b/src/block_proof.cpp
new file mode 100644
index 0000000000..8465a781e1
--- /dev/null
+++ b/src/block_proof.cpp
@@ -0,0 +1,62 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2018 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 <pow.h>
+
+#include <chain.h>
+#include <primitives/block.h>
+#include <script/interpreter.h>
+#include <script/generic.hpp>
+
+bool CheckChallenge(const CBlockHeader& block, const CBlockIndex& indexLast, const Consensus::Params& params)
+{
+    if (g_signed_blocks) {
+        return block.proof.challenge == indexLast.proof.challenge;
+    } else {
+        return block.nBits == GetNextWorkRequired(&indexLast, &block, params);
+    }
+}
+
+void ResetChallenge(CBlockHeader& block, const CBlockIndex& indexLast, const Consensus::Params& params)
+{
+    block.proof.challenge = indexLast.proof.challenge;
+}
+
+static bool CheckProofGeneric(const CBlockHeader& block, const Consensus::Params& params, const CScript& challenge)
+{
+    if (block.GetHash() == params.hashGenesisBlock)
+       return true;
+
+    if (block.proof.solution.size() > params.max_block_signature_size) {
+        return false;
+    }
+
+    // Some anti-DoS flags, though consensus.max_block_signature_size caps the possible
+    // danger in malleation of the block witness data.
+    unsigned int proof_flags = SCRIPT_VERIFY_P2SH // For cleanstack evalution under segwit flag
+        | SCRIPT_VERIFY_STRICTENC // Minimally-sized DER sigs
+        | SCRIPT_VERIFY_NULLDUMMY // No extra data stuffed into OP_CMS witness
+        | SCRIPT_VERIFY_CLEANSTACK // No extra pushes leftover in witness
+        | SCRIPT_VERIFY_MINIMALDATA // Pushes are minimally-sized
+        | SCRIPT_VERIFY_SIGPUSHONLY // Witness is push-only
+        | SCRIPT_VERIFY_LOW_S // Stop easiest signature fiddling
+        | SCRIPT_VERIFY_WITNESS // Required for cleanstack eval in VerifyScript
+        | SCRIPT_NO_SIGHASH_BYTE; // non-Check(Multi)Sig signatures will not have sighash byte
+    return GenericVerifyScript(block.proof.solution, challenge, proof_flags, block);
+}
+
+bool CheckProof(const CBlockHeader& block, const Consensus::Params& params)
+{
+    if (g_signed_blocks) {
+        return CheckProofGeneric(block, params, params.signblockscript);
+    } else {
+        return CheckProofOfWork(block.GetHash(), block.nBits, params);
+    }
+}
+
+void ResetProof(CBlockHeader& block)
+{
+    block.proof.solution.clear();
+}
diff --git a/src/block_proof.h b/src/block_proof.h
new file mode 100644
index 0000000000..f0dcd6a8e8
--- /dev/null
+++ b/src/block_proof.h
@@ -0,0 +1,26 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_BLOCK_PROOF_H
+#define BITCOIN_BLOCK_PROOF_H
+
+#include <consensus/params.h>
+
+#include <stdint.h>
+
+class CBlockHeader;
+class CBlockIndex;
+class CProof;
+class CScript;
+
+// Elements signed chain functionality
+
+/** Check on header proof, depending on chain type, PoW or signed **/
+bool CheckProof(const CBlockHeader& block, const Consensus::Params&);
+void ResetProof(CBlockHeader& block);
+bool CheckChallenge(const CBlockHeader& block, const CBlockIndex& indexLast, const Consensus::Params&);
+void ResetChallenge(CBlockHeader& block, const CBlockIndex& indexLast, const Consensus::Params&);
+
+#endif // BITCOIN_BLOCK_PROOF_H