Verify inclusion proofs with multiple leaves (#58)

* support multiple leaves while proving

* add test and debug

* format appends

* add comment to VerifyInclusion

* add more docs

Co-authored-by: John Adler <adlerjohn@users.noreply.github.com>

Co-authored-by: John Adler <adlerjohn@users.noreply.github.com>

fuzz_test.go

@@ -8,7 +8,7 @@ import (
 
 	"github.com/celestiaorg/nmt"
 	"github.com/celestiaorg/nmt/namespace"
-	"github.com/google/gofuzz"
+	fuzz "github.com/google/gofuzz"
 )
 
 func TestFuzzProveVerifyNameSpace(t *testing.T) {
@@ -72,7 +72,7 @@ func TestFuzzProveVerifyNameSpace(t *testing.T) {
 				if err != nil {
 					t.Fatalf("error on Prove(%v): %v", i, err)
 				}
-				if ok := singleItemProof.VerifyInclusion(hash, data[i][:size], data[i][size:], treeRoot); !ok {
+				if ok := singleItemProof.VerifyInclusion(hash, data[i][:size], [][]byte{data[i][size:]}, treeRoot); !ok {
 					t.Fatalf("expected VerifyInclusion() == true; data = %#v; proof = %#v", data[i], singleItemProof)
 				}
 				leafIdx++

nmt_test.go

@@ -277,7 +277,7 @@ func TestNamespacedMerkleTree_ProveNamespace_Ranges_And_Verify(t *testing.T) {
 					if err != nil {
 						t.Fatalf("unexpected error on Prove(): %v", err)
 					}
-					gotChecksOut := gotSingleProof.VerifyInclusion(sha256.New(), data.ID, data.Data, n.Root())
+					gotChecksOut := gotSingleProof.VerifyInclusion(sha256.New(), data.ID, [][]byte{data.Data}, n.Root())
 					if !gotChecksOut {
 						t.Errorf("Proof.VerifyInclusion() gotChecksOut: %v, want: true", gotChecksOut)
 					}
@@ -467,7 +467,7 @@ func TestIgnoreMaxNamespace(t *testing.T) {
 				if err != nil {
 					t.Fatalf("ProveNamespace() unexpected error: %v", err)
 				}
-				if !singleProof.VerifyInclusion(hash, d.NamespaceID(), d.Data(), tree.Root()) {
+				if !singleProof.VerifyInclusion(hash, d.NamespaceID(), [][]byte{d.Data()}, tree.Root()) {
 					t.Errorf("VerifyInclusion() failed on data: %#v with index: %v", d, idx)
 				}
 				if gotIgnored := singleProof.IsMaxNamespaceIDIgnored(); gotIgnored != tc.ignoreMaxNamespace {

proof.go

@@ -206,10 +206,19 @@ func (proof Proof) verifyLeafHashes(nth *Hasher, verifyCompleteness bool, nID na
 	return bytes.Equal(tree.Root(), root)
 }
 
-func (proof Proof) VerifyInclusion(h hash.Hash, nid namespace.ID, data []byte, root []byte) bool {
+// VerifyInclusion checks that the inclusion proof is valid by using leaf data
+// and the provided proof to regenerate and compare the root. Note that the leaf
+// data should not contain the prefixed namespace, unlike the tree.Push method,
+// which takes prefixed data. All leaves implicitly have the same namespace ID: `nid`.
+func (proof Proof) VerifyInclusion(h hash.Hash, nid namespace.ID, leaves [][]byte, root []byte) bool {
 	nth := NewNmtHasher(h, nid.Size(), proof.isMaxNamespaceIDIgnored)
-	leafData := append(nid, data...)
-	return proof.verifyLeafHashes(nth, false, nid, [][]byte{nth.HashLeaf(leafData)}, root)
+	hashes := make([][]byte, len(leaves))
+	for i, d := range leaves {
+		leafData := append(append(make([]byte, 0, len(d)+len(nid)), nid...), d...)
+		hashes[i] = nth.HashLeaf(leafData)
+	}
+
+	return proof.verifyLeafHashes(nth, false, nid, hashes, root)
 }
 
 // nextSubtreeSize returns the size of the subtree adjacent to start that does

proof_test.go

@@ -1,6 +1,7 @@
 package nmt
 
 import (
+	"bytes"
 	"crypto/sha256"
 	"testing"
 
@@ -90,3 +91,67 @@ func rangeProof(t *testing.T, n *NamespacedMerkleTree, start, end int) [][]byte
 	}
 	return incompleteRange
 }
+
+func TestProof_MultipleLeaves(t *testing.T) {
+	n := New(sha256.New())
+	ns := []byte{1, 2, 3, 4, 5, 6, 7, 8}
+	rawData := [][]byte{
+		bytes.Repeat([]byte{1}, 100),
+		bytes.Repeat([]byte{2}, 100),
+		bytes.Repeat([]byte{3}, 100),
+		bytes.Repeat([]byte{4}, 100),
+		bytes.Repeat([]byte{5}, 100),
+		bytes.Repeat([]byte{6}, 100),
+		bytes.Repeat([]byte{7}, 100),
+		bytes.Repeat([]byte{8}, 100),
+	}
+
+	for _, d := range rawData {
+		err := n.Push(safeAppend(ns, d))
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	type args struct {
+		start, end int
+		root       []byte
+	}
+	tests := []struct {
+		name string
+		args args
+		want bool
+	}{
+		{
+			"3rd through 5th leaf", args{2, 4, n.Root()}, true,
+		},
+		{
+			"single leaf", args{2, 3, n.Root()}, true,
+		},
+		{
+			"first leaf", args{0, 1, n.Root()}, true,
+		},
+		{
+			"most leaves", args{0, 7, n.Root()}, true,
+		},
+		{
+			"most leaves", args{0, 7, bytes.Repeat([]byte{1}, 48)}, false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			proof, err := n.ProveRange(tt.args.start, tt.args.end)
+			if err != nil {
+				t.Fatal(err)
+			}
+			got := proof.VerifyInclusion(sha256.New(), ns, rawData[tt.args.start:tt.args.end], tt.args.root)
+			if got != tt.want {
+				t.Errorf("VerifyInclusion() got = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func safeAppend(id, data []byte) []byte {
+	return append(append(make([]byte, 0, len(id)+len(data)), id...), data...)
+}