Expand and test malleability functions.

Makefile.am

@@ -215,6 +215,7 @@ test_libbitcoin_system_test_SOURCES = \
     test/typelets.cpp \
     test/types.cpp \
     test/chain/block.cpp \
+    test/chain/block_malleable.cpp \
     test/chain/chain_state.cpp \
     test/chain/checkpoint.cpp \
     test/chain/compact.cpp \

builds/cmake/CMakeLists.txt

@@ -698,6 +698,7 @@ if (with-tests)
         "../../test/typelets.cpp"
         "../../test/types.cpp"
         "../../test/chain/block.cpp"
+        "../../test/chain/block_malleable.cpp"
         "../../test/chain/chain_state.cpp"
         "../../test/chain/checkpoint.cpp"
         "../../test/chain/compact.cpp"

builds/msvc/vs2022/libbitcoin-system-test/libbitcoin-system-test.vcxproj

@@ -73,6 +73,7 @@
     <ClCompile Include="..\..\..\..\test\chain\block.cpp">
       <ObjectFileName>$(IntDir)test_chain_block.obj</ObjectFileName>
     </ClCompile>
+    <ClCompile Include="..\..\..\..\test\chain\block_malleable.cpp" />
     <ClCompile Include="..\..\..\..\test\chain\chain_state.cpp" />
     <ClCompile Include="..\..\..\..\test\chain\checkpoint.cpp" />
     <ClCompile Include="..\..\..\..\test\chain\compact.cpp" />

builds/msvc/vs2022/libbitcoin-system-test/libbitcoin-system-test.vcxproj.filters

@@ -105,6 +105,9 @@
     <ClCompile Include="..\..\..\..\test\chain\block.cpp">
       <Filter>src\chain</Filter>
     </ClCompile>
+    <ClCompile Include="..\..\..\..\test\chain\block_malleable.cpp">
+      <Filter>src\chain</Filter>
+    </ClCompile>
     <ClCompile Include="..\..\..\..\test\chain\chain_state.cpp">
       <Filter>src\chain</Filter>
     </ClCompile>

include/bitcoin/system/chain/block.hpp

@@ -41,6 +41,7 @@ class BC_API block
 public:
     DEFAULT_COPY_MOVE_DESTRUCT(block);
 
+    typedef std_vector<size_t> sizes;
     typedef std::shared_ptr<const block> cptr;
 
     /// Constructors.
@@ -90,13 +91,16 @@ class BC_API block
     uint64_t fees() const NOEXCEPT;
     uint64_t claim() const NOEXCEPT;
     hash_digest hash() const NOEXCEPT;
-    bool is_malleable() const NOEXCEPT;
-    bool is_malleable_duplicate() const NOEXCEPT;
-    bool is_malleable_coincident() const NOEXCEPT;
     bool is_segregated() const NOEXCEPT;
     size_t serialized_size(bool witness) const NOEXCEPT;
     size_t signature_operations(bool bip16, bool bip141) const NOEXCEPT;
 
+    /// Computed malleation properties.
+    bool is_malleable() const NOEXCEPT;
+    bool is_malleable64() const NOEXCEPT;
+    bool is_malleable32() const NOEXCEPT;
+    bool is_malleated32() const NOEXCEPT;
+
     /// Validation.
     /// -----------------------------------------------------------------------
 
@@ -115,6 +119,19 @@ class BC_API block
     block(const chain::header::cptr& header,
         const chain::transactions_cptr& txs, bool valid) NOEXCEPT;
 
+    size_t malleated32_size() const NOEXCEPT;
+    bool is_malleated32(size_t width) const NOEXCEPT;
+    static constexpr bool is_malleable32_size(size_t set, size_t width) NOEXCEPT
+    {
+        // Malleable when set is odd at width depth and not before and not one.
+        // This is the only case in which Merkle clones the last item in a set.
+        for (auto depth = one; depth <= width; depth *= two, set = to_half(set))
+            if (is_odd(set))
+                return depth == width && !is_one(set);
+
+        return false;
+    }
+
     /// Check (context free).
     /// -----------------------------------------------------------------------
 

src/chain/block.cpp

@@ -438,40 +438,66 @@ bool block::is_hash_limit_exceeded() const NOEXCEPT
     return hashes.size() > hash_limit;
 }
 
-// This is not part of validation. Should be called after *invalidation* to
-// determine if the invalidity is universal (otherwise do not cache invalid),
-// and as an abbreviated validation when under checkpoint/milestone.
-// lists.linuxfoundation.org/pipermail/bitcoin-dev/2019-February/016697.html
 bool block::is_malleable() const NOEXCEPT
 {
-    return is_malleable_coincident() || is_malleable_duplicate();
+    return is_malleable64() || is_malleable32();
 }
 
-// Repeated tx hashes is a subset of is_internal_double_spend.
-// This form of malleability also implies current block instance is invalid.
-bool block::is_malleable_duplicate() const NOEXCEPT
+bool block::is_malleable32() const NOEXCEPT
 {
-    // A set is used to collapse duplicates.
-    std::set<hash_digest> hashes;
+    const auto unmalleated = txs_->size();
+    for (auto mally = one; mally <= unmalleated; mally *= two)
+        if (is_malleable32_size(unmalleated, mally))
+            return true;
 
-    BC_PUSH_WARNING(NO_THROW_IN_NOEXCEPT)
-    for (const auto& tx: *txs_)
-        hashes.insert(tx->hash(false));
-    BC_POP_WARNING()
-
-    return hashes.size() == txs_->size();
+    return false;
+}
+
+bool block::is_malleated32() const NOEXCEPT
+{
+    return !is_zero(malleated32_size());
+}
+
+// protected
+// The size of an actual malleation of this block, or zero.
+size_t block::malleated32_size() const NOEXCEPT
+{
+    const auto malleated = txs_->size();
+    for (auto mally = one; mally <= to_half(malleated); mally *= two)
+        if (is_malleable32_size(malleated - mally, mally) &&
+            is_malleated32(mally))
+            return mally;
+
+    return zero;
+}
+
+// protected
+// True if the last width set of tx hashes repeats.
+bool block::is_malleated32(size_t width) const NOEXCEPT
+{
+    const auto malleated = txs_->size();
+    if (is_zero(width) || width > to_half(malleated))
+        return false;
+
+    auto mally = txs_->rbegin();
+    auto legit = std::next(mally, width);
+    while (!is_zero(width--))
+        if ((*mally++)->hash(false) != (*legit++)->hash(false))
+            return false;
+
+    return true;
 }
 
 // If all non-witness tx serializations are 64 bytes the id is malleable.
 // This form of malleability does not imply current block instance is invalid.
-bool block::is_malleable_coincident() const NOEXCEPT
+bool block::is_malleable64() const NOEXCEPT
 {
-    const auto two_leaf_size = [](const transaction::cptr& tx) NOEXCEPT
+    const auto two_leaves = [](const transaction::cptr& tx) NOEXCEPT
     {
         return tx->serialized_size(false) == two * hash_size;
     };
 
-    return std::all_of(txs_->begin(), txs_->end(), two_leaf_size);
+    return !is_empty() && std::all_of(txs_->begin(), txs_->end(), two_leaves);
 }
 
 bool block::is_segregated() const NOEXCEPT