Do not store Merkle branches in the wallet.

Assume that when a wallet transaction has a valid block hash and transaction position
in it, the transaction is actually there. We're already trusting wallet data in a
much more fundamental way anyway.

To prevent backward compatibility issues, a new record is used for storing the
block locator in the wallet. Old wallets will see a wallet file synchronized up
to the genesis block, and rescan automatically.

2 files changed, 4 insertions, 45 deletions

diff --git a/src/primitives/block.cpp b/src/primitives/block.cpp
index 5b9c13d870..7a58074d24 100644
--- a/src/primitives/block.cpp
+++ b/src/primitives/block.cpp
@@ -15,7 +15,7 @@ uint256 CBlockHeader::GetHash() const
     return SerializeHash(*this);
 }
 
-uint256 CBlock::BuildMerkleTree(bool* fMutated) const
+uint256 CBlock::ComputeMerkleRoot(bool* fMutated) const
 {
     /* WARNING! If you're reading this because you're learning about crypto
        and/or designing a new system that will use merkle trees, keep in mind
@@ -52,7 +52,7 @@ uint256 CBlock::BuildMerkleTree(bool* fMutated) const
        known ways of changing the transactions without affecting the merkle
        root.
     */
-    vMerkleTree.clear();
+    std::vector<uint256> vMerkleTree;
     vMerkleTree.reserve(vtx.size() * 2 + 16); // Safe upper bound for the number of total nodes.
     for (std::vector<CTransaction>::const_iterator it(vtx.begin()); it != vtx.end(); ++it)
         vMerkleTree.push_back(it->GetHash());
@@ -78,37 +78,6 @@ uint256 CBlock::BuildMerkleTree(bool* fMutated) const
     return (vMerkleTree.empty() ? uint256() : vMerkleTree.back());
 }
 
-std::vector<uint256> CBlock::GetMerkleBranch(int nIndex) const
-{
-    if (vMerkleTree.empty())
-        BuildMerkleTree();
-    std::vector<uint256> vMerkleBranch;
-    int j = 0;
-    for (int nSize = vtx.size(); nSize > 1; nSize = (nSize + 1) / 2)
-    {
-        int i = std::min(nIndex^1, nSize-1);
-        vMerkleBranch.push_back(vMerkleTree[j+i]);
-        nIndex >>= 1;
-        j += nSize;
-    }
-    return vMerkleBranch;
-}
-
-uint256 CBlock::CheckMerkleBranch(uint256 hash, const std::vector<uint256>& vMerkleBranch, int nIndex)
-{
-    if (nIndex == -1)
-        return uint256();
-    for (std::vector<uint256>::const_iterator it(vMerkleBranch.begin()); it != vMerkleBranch.end(); ++it)
-    {
-        if (nIndex & 1)
-            hash = Hash(BEGIN(*it), END(*it), BEGIN(hash), END(hash));
-        else
-            hash = Hash(BEGIN(hash), END(hash), BEGIN(*it), END(*it));
-        nIndex >>= 1;
-    }
-    return hash;
-}
-
 std::string CBlock::ToString() const
 {
     std::stringstream s;
@@ -123,9 +92,5 @@ std::string CBlock::ToString() const
     {
         s << "  " << vtx[i].ToString() << "\n";
     }
-    s << "  vMerkleTree: ";
-    for (unsigned int i = 0; i < vMerkleTree.size(); i++)
-        s << " " << vMerkleTree[i].ToString();
-    s << "\n";
     return s.str();
 }
diff --git a/src/primitives/block.h b/src/primitives/block.h
index 59f46deb1c..7fe8c84cb7 100644
--- a/src/primitives/block.h
+++ b/src/primitives/block.h
@@ -77,9 +77,6 @@ public:
     // network and disk
     std::vector<CTransaction> vtx;
 
-    // memory only
-    mutable std::vector<uint256> vMerkleTree;
-
     CBlock()
     {
         SetNull();
@@ -103,7 +100,6 @@ public:
     {
         CBlockHeader::SetNull();
         vtx.clear();
-        vMerkleTree.clear();
     }
 
     CBlockHeader GetBlockHeader() const
@@ -118,14 +114,12 @@ public:
         return block;
     }
 
-    // Build the in-memory merkle tree for this block and return the merkle root.
+    // Build the merkle tree for this block and return the merkle root.
     // If non-NULL, *mutated is set to whether mutation was detected in the merkle
     // tree (a duplication of transactions in the block leading to an identical
     // merkle root).
-    uint256 BuildMerkleTree(bool* mutated = NULL) const;
+    uint256 ComputeMerkleRoot(bool* mutated = NULL) const;
 
-    std::vector<uint256> GetMerkleBranch(int nIndex) const;
-    static uint256 CheckMerkleBranch(uint256 hash, const std::vector<uint256>& vMerkleBranch, int nIndex);
     std::string ToString() const;
 };