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feat: add support for subtree root verification #260

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Jul 16, 2024
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56 changes: 41 additions & 15 deletions nmt.go
Original file line number Diff line number Diff line change
Expand Up @@ -107,9 +107,9 @@

// namespaceRanges can be used to efficiently look up the range for an
// existing namespace without iterating through the leaves. The map key is
// the string representation of a namespace.ID and the leafRange indicates
// the string representation of a namespace.ID and the LeafRange indicates
// the range of the leaves matching that namespace ID in the tree
namespaceRanges map[string]leafRange
namespaceRanges map[string]LeafRange
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This exports the LeafRange to be used downstream

// minNID is the minimum namespace ID of the leaves
minNID namespace.ID
// maxNID is the maximum namespace ID of the leaves
Expand Down Expand Up @@ -151,7 +151,7 @@
visit: opts.NodeVisitor,
leaves: make([][]byte, 0, opts.InitialCapacity),
leafHashes: make([][]byte, 0, opts.InitialCapacity),
namespaceRanges: make(map[string]leafRange),
namespaceRanges: make(map[string]LeafRange),
minNID: bytes.Repeat([]byte{0xFF}, int(opts.NamespaceIDSize)),
maxNID: bytes.Repeat([]byte{0x00}, int(opts.NamespaceIDSize)),
}
Expand Down Expand Up @@ -436,7 +436,7 @@
// This is a faster version of this code snippet:
// https://github.com/celestiaorg/celestiaorg-prototype/blob/2aeca6f55ad389b9d68034a0a7038f80a8d2982e/simpleblock.go#L106-L117
foundRng, found := n.namespaceRanges[string(nID)]
return found, foundRng.start, foundRng.end
return found, foundRng.Start, foundRng.End
}

// NamespaceSize returns the underlying namespace size. Note that all namespaced
Expand Down Expand Up @@ -590,14 +590,14 @@
lastNsStr := string(lastPushed[:n.treeHasher.NamespaceSize()])
lastRange, found := n.namespaceRanges[lastNsStr]
if !found {
n.namespaceRanges[lastNsStr] = leafRange{
start: lastIndex,
end: lastIndex + 1,
n.namespaceRanges[lastNsStr] = LeafRange{
Start: lastIndex,
End: lastIndex + 1,
}
} else {
n.namespaceRanges[lastNsStr] = leafRange{
start: lastRange.start,
end: lastRange.end + 1,
n.namespaceRanges[lastNsStr] = LeafRange{
Start: lastRange.Start,
End: lastRange.End + 1,
}
}
}
Expand Down Expand Up @@ -644,11 +644,37 @@
}
}

type leafRange struct {
// start and end denote the indices of a leaf in the tree. start ranges from
// 0 up to the total number of leaves minus 1 end ranges from 1 up to the
// total number of leaves end is non-inclusive
start, end int
// ComputeSubtreeRoot takes a leaf range and returns the corresponding subtree root.
// Also, it requires the start and end range to correctly reference an inner node.
func (n *NamespacedMerkleTree) ComputeSubtreeRoot(start, end int) ([]byte, error) {
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if start < 0 {
return nil, fmt.Errorf("start %d shouldn't be strictly negative", start)
}
if end <= start {
return nil, fmt.Errorf("end %d should be stricly bigger than start %d", end, start)
}
uStart, err := safeIntToUint(start)
if err != nil {
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return nil, err

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}
uEnd, err := safeIntToUint(end)
if err != nil {
return nil, err

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}
// check if the provided range correctly references an inner node.
// calculates the ideal tree from the provided range, and verifies if it is the same as the range
if idealTreeRange := nextSubtreeSize(uint64(uStart), uint64(uEnd)); end-start != idealTreeRange {
return nil, fmt.Errorf("the provided range [%d, %d) does not construct a valid subtree root range", start, end)
}
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return n.computeRoot(start, end)
}
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type LeafRange struct {
// Start and End denote the indices of a leaf in the tree.
// Start ranges from 0 up to the total number of leaves minus 1.
// End ranges from 1 up to the total number of leaves.
// End is non-inclusive
Start, End int
}

// MinNamespace extracts the minimum namespace ID from a given namespace hash,
Expand Down
145 changes: 145 additions & 0 deletions nmt_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -862,6 +862,20 @@ func exampleNMT(nidSize int, ignoreMaxNamespace bool, leavesNIDs ...byte) *Names
return tree
}

// exampleNMT2 Replica of exampleNMT except that it uses the namespace IDs in the
// leaves instead of the index.
func exampleNMT2(nidSize int, ignoreMaxNamespace bool, leavesNIDs ...byte) *NamespacedMerkleTree {
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tree := New(sha256.New(), NamespaceIDSize(nidSize), IgnoreMaxNamespace(ignoreMaxNamespace))
for _, nid := range leavesNIDs {
namespace := bytes.Repeat([]byte{nid}, nidSize)
d := append(namespace, []byte(fmt.Sprintf("leaf_%d", nid))...)
if err := tree.Push(d); err != nil {
panic(fmt.Sprintf("unexpected error: %v", err))
}
}
return tree
}
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func swap(slice [][]byte, i int, j int) {
temp := slice[i]
slice[i] = slice[j]
Expand Down Expand Up @@ -1175,3 +1189,134 @@ func TestForcedOutOfOrderNamespacedMerkleTree(t *testing.T) {
assert.NoError(t, err)
}
}

func TestComputeSubtreeRoot(t *testing.T) {
n := exampleNMT2(1, true, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
tests := []struct {
start, end int
tree *NamespacedMerkleTree
expectedRoot []byte
expectError bool
}{
{
start: 0,
end: 16,
tree: n,
expectedRoot: func() []byte {
root, err := n.Root()
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This updates the state of the original tree n, can we create another instance of the tree instead similar to other test cases i.e.,

exampleNMT2(1, true, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15).Root()

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what's the problem with updating the original tree with a root in a test? that would make the other tests not recalculate it which is good, no?

require.NoError(t, err)
return root
}(),
},
{
start: 0,
end: 8,
tree: n,
expectedRoot: func() []byte {
// because the root of the range [0,8) coincides with the root of this tree
root, err := exampleNMT2(1, true, 0, 1, 2, 3, 4, 5, 6, 7).Root()
require.NoError(t, err)
return root
}(),
},
{
start: 8,
end: 16,
tree: n,
expectedRoot: func() []byte {
// because the root of the range [8,16) coincides with the root of this tree
root, err := exampleNMT2(1, true, 8, 9, 10, 11, 12, 13, 14, 15).Root()
require.NoError(t, err)
return root
}(),
},
{
start: 8,
end: 12,
tree: n,
expectedRoot: func() []byte {
// because the root of the range [8,12) coincides with the root of this tree
root, err := exampleNMT2(1, true, 8, 9, 10, 11).Root()
require.NoError(t, err)
return root
}(),
},
{
start: 4,
end: 8,
tree: n,
expectedRoot: func() []byte {
// because the root of the range [4,8) coincides with the root of this tree
root, err := exampleNMT2(1, true, 4, 5, 6, 7).Root()
require.NoError(t, err)
return root
}(),
},
{
start: 4,
end: 6,
tree: n,
expectedRoot: func() []byte {
// because the root of the range [4,6) coincides with the root of this tree
root, err := exampleNMT2(1, true, 4, 5).Root()
require.NoError(t, err)
return root
}(),
},
{
start: 4,
end: 5,
tree: n,
expectedRoot: func() []byte {
// because the root of the range [4,5) coincides with the root of this tree
root, err := exampleNMT2(1, true, 4).Root()
require.NoError(t, err)
return root
}(),
},
{ // doesn't correctly reference an inner node
start: 2,
end: 6,
tree: n,
expectError: true,
},
{
start: -1, // invalid start
end: 4,
tree: n,
expectError: true,
},
{
start: 4,
end: 4, // start == end
tree: n,
expectError: true,
},
{
start: 5, // start >= end
end: 4,
tree: n,
expectError: true,
},
{
start: 0,
end: 16,
tree: func() *NamespacedMerkleTree {
return exampleNMT2(1, true, 0, 1, 2, 3, 4) // tree leaves are not a power of 2
}(),
expectError: true,
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The reason that this test case errors out is that the the range of the proof is larger than the size of the tree, hence, the comment tree leaves are not a power of 2 does not indicate why an error is expected, right?
To my understanding, the correct behaviour of this specific function i.e, ComputeSubtreeRoot does not require the tree to be power of two.

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depends on: #260 (comment)

},
}

for _, tt := range tests {
t.Run(fmt.Sprintf("treeSize=%d,start=%d,end=%d", tt.tree.Size(), tt.start, tt.end), func(t *testing.T) {
root, err := tt.tree.ComputeSubtreeRoot(tt.start, tt.end)
if tt.expectError {
assert.Error(t, err)
} else {
assert.NoError(t, err)
assert.Equal(t, tt.expectedRoot, root)
}
})
}
}
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