feat: Add support for SMT ExclusionProofs

Makefile

@@ -1,5 +1,5 @@
 DOCKER := $(shell which docker)
-HTTPS_GIT := https://github.com/cosmos/cosmos-sdk.git
+HTTPS_GIT := https://github.com/cosmos/ics23.git
 
 ##### GO commands #####
 

go/compress.go

@@ -60,6 +60,14 @@ func compressEntry(entry *BatchEntry, lookup *[]*InnerOp, registry map[string]in
 		}
 	}
 
+	if exclusion := entry.GetExclusion(); exclusion != nil {
+		return &CompressedBatchEntry{
+			Proof: &CompressedBatchEntry_Exclusion{
+				Exclusion: compressExclusion(exclusion, lookup, registry),
+			},
+		}
+	}
+
 	non := entry.GetNonexist()
 	return &CompressedBatchEntry{
 		Proof: &CompressedBatchEntry_Nonexist{
@@ -88,6 +96,23 @@ func compressExist(exist *ExistenceProof, lookup *[]*InnerOp, registry map[strin
 	return res
 }
 
+func compressExclusion(exclusion *ExclusionProof, lookup *[]*InnerOp, registry map[string]int32) *CompressedExclusionProof {
+	if exclusion == nil {
+		return nil
+	}
+	res := &CompressedExclusionProof{
+		Key:             exclusion.Key,
+		ActualPath:      exclusion.ActualPath,
+		ActualValueHash: exclusion.ActualValueHash,
+		Leaf:            exclusion.Leaf,
+		Path:            make([]int32, len(exclusion.Path)),
+	}
+	for i, step := range exclusion.Path {
+		res.Path[i] = compressStep(step, lookup, registry)
+	}
+	return res
+}
+
 func compressStep(step *InnerOp, lookup *[]*InnerOp, registry map[string]int32) int32 {
 	bz, err := step.Marshal()
 	if err != nil {
@@ -131,6 +156,14 @@ func decompressEntry(entry *CompressedBatchEntry, lookup []*InnerOp) *BatchEntry
 		}
 	}
 
+	if exclusion := entry.GetExclusion(); exclusion != nil {
+		return &BatchEntry{
+			Proof: &BatchEntry_Exclusion{
+				Exclusion: decompressExclusion(exclusion, lookup),
+			},
+		}
+	}
+
 	non := entry.GetNonexist()
 	return &BatchEntry{
 		Proof: &BatchEntry_Nonexist{
@@ -158,3 +191,20 @@ func decompressExist(exist *CompressedExistenceProof, lookup []*InnerOp) *Existe
 	}
 	return res
 }
+
+func decompressExclusion(exclusion *CompressedExclusionProof, lookup []*InnerOp) *ExclusionProof {
+	if exclusion == nil {
+		return nil
+	}
+	res := &ExclusionProof{
+		Key:             exclusion.Key,
+		ActualPath:      exclusion.ActualPath,
+		ActualValueHash: exclusion.ActualValueHash,
+		Leaf:            exclusion.Leaf,
+		Path:            make([]*InnerOp, len(exclusion.Path)),
+	}
+	for i, step := range exclusion.Path {
+		res.Path[i] = lookup[step]
+	}
+	return res
+}

go/ics23.go

@@ -52,11 +52,35 @@ func VerifyMembership(spec *ProofSpec, root CommitmentRoot, proof *CommitmentPro
 func VerifyNonMembership(spec *ProofSpec, root CommitmentRoot, proof *CommitmentProof, key []byte) bool {
 	// decompress it before running code (no-op if not compressed)
 	proof = Decompress(proof)
-	np := getNonExistProofForKey(spec, proof, key)
-	if np == nil {
+	var err error
+	switch proof.Proof.(type) {
+	case *CommitmentProof_Nonexist:
+		np := getNonExistProofForKey(spec, proof, key)
+		if np == nil {
+			return false
+		}
+		err = np.Verify(spec, root, key)
+	case *CommitmentProof_Exclusion:
+		ex := getExclusionProofForKey(proof, key)
+		if ex == nil {
+			return false
+		}
+		err = ex.Verify(spec, root, key)
+	case *CommitmentProof_Batch:
+		np := getNonExistProofForKey(spec, proof, key)
+		ex := getExclusionProofForKey(proof, key)
+		if np == nil && ex == nil {
+			return false
+		}
+		if np != nil {
+			err = np.Verify(spec, root, key)
+		} else {
+			err = ex.Verify(spec, root, key)
+		}
+	default:
 		return false
 	}
-	err := np.Verify(spec, root, key)
+
 	return err == nil
 }
 
@@ -103,6 +127,13 @@ func CombineProofs(proofs []*CommitmentProof) (*CommitmentProof, error) {
 				},
 			}
 			entries = append(entries, entry)
+		} else if excl := proof.GetExclusion(); excl != nil {
+			entry := &BatchEntry{
+				Proof: &BatchEntry_Exclusion{
+					Exclusion: excl,
+				},
+			}
+			entries = append(entries, entry)
 		} else if non := proof.GetNonexist(); non != nil {
 			entry := &BatchEntry{
 				Proof: &BatchEntry_Nonexist{
@@ -148,6 +179,23 @@ func getExistProofForKey(proof *CommitmentProof, key []byte) *ExistenceProof {
 	return nil
 }
 
+func getExclusionProofForKey(proof *CommitmentProof, key []byte) *ExclusionProof {
+	switch p := proof.Proof.(type) {
+	case *CommitmentProof_Exclusion:
+		ep := p.Exclusion
+		if bytes.Equal(ep.Key, key) {
+			return ep
+		}
+	case *CommitmentProof_Batch:
+		for _, sub := range p.Batch.Entries {
+			if ep := sub.GetExclusion(); ep != nil && bytes.Equal(ep.Key, key) {
+				return ep
+			}
+		}
+	}
+	return nil
+}
+
 func getNonExistProofForKey(spec *ProofSpec, proof *CommitmentProof, key []byte) *NonExistenceProof {
 	switch p := proof.Proof.(type) {
 	case *CommitmentProof_Nonexist:

go/proof.go

@@ -43,7 +43,7 @@ var TendermintSpec = &ProofSpec{
 	},
 }
 
-// SmtSpec constrains the format for SMT proofs (as implemented by github.com/celestiaorg/smt)
+// SmtSpec constrains the format for SMT proofs (as implemented by github.com/pokt-network/smt)
 var SmtSpec = &ProofSpec{
 	LeafSpec: &LeafOp{
 		Hash:         HashOp_SHA256,
@@ -86,13 +86,18 @@ func (p *CommitmentProof) Calculate() (CommitmentRoot, error) {
 		return v.Exist.Calculate()
 	case *CommitmentProof_Nonexist:
 		return v.Nonexist.Calculate()
+	case *CommitmentProof_Exclusion:
+		return v.Exclusion.Calculate()
 	case *CommitmentProof_Batch:
 		if len(v.Batch.GetEntries()) == 0 || v.Batch.GetEntries()[0] == nil {
 			return nil, errors.New("batch proof has empty entry")
 		}
 		if e := v.Batch.GetEntries()[0].GetExist(); e != nil {
 			return e.Calculate()
 		}
+		if x := v.Batch.GetEntries()[0].GetExclusion(); x != nil {
+			return x.Calculate()
+		}
 		if n := v.Batch.GetEntries()[0].GetNonexist(); n != nil {
 			return n.Calculate()
 		}
@@ -163,6 +168,106 @@ func (p *ExistenceProof) calculate(spec *ProofSpec) (CommitmentRoot, error) {
 	return res, nil
 }
 
+func (p *ExclusionProof) Calculate() (CommitmentRoot, error) {
+	if p.GetLeaf() == nil {
+		return nil, errors.New("exclusion proof needs defined LeafOp")
+	}
+
+	// As the actual_path and actual_value_hash are already hashed both the
+	// prehash_key and prehash_value fields should be set to HashOp_NO_HASH
+	// this is because they have been populated from the unrelated leaf found
+	// in place of the key we were looking for, hashing them again would
+	// result in an incorrect leaf node hash and invalidate the proof.
+	if p.Leaf.PrehashKey != HashOp_NO_HASH {
+		return nil, errors.New("exclusion proof must have leaf with PrehashKey == NO_HASH")
+	}
+	if p.Leaf.PrehashValue != HashOp_NO_HASH {
+		return nil, errors.New("exclusion proof must have leaf with PrehashValue == NO_HASH")
+	}
+
+	// leaf step takes the key and value as input
+	res, err := p.Leaf.Apply(p.ActualPath, p.ActualValueHash)
+	if err != nil {
+		return nil, fmt.Errorf("leaf, %w", err)
+	}
+	// check if the actual value was a placeholder and replace with empty hash
+	// assumes the placeholder value is [32]byte
+	if bytes.Equal(p.ActualValueHash, SmtSpec.InnerSpec.EmptyChild) {
+		res = SmtSpec.InnerSpec.EmptyChild
+	}
+
+	// the rest just take the output of the last step (reducing it)
+	for _, step := range p.Path {
+		res, err = step.Apply(res)
+		if err != nil {
+			return nil, fmt.Errorf("inner, %w", err)
+		}
+	}
+	return res, nil
+}
+
+// Verify the ExclusionProof by checking the existence of either:
+//  1. An unrelated leaf where the leaf we are looking for should be
+//  2. A placeholder leaf where the leaf we are looking for is
+//
+// Ref: https://github.com/pokt-network/pocket/blob/main/ibc/docs/ics23.md#proof-verification
+func (p *ExclusionProof) Verify(spec *ProofSpec, root CommitmentRoot, key []byte) error {
+	if err := p.CheckAgainstSpec(spec); err != nil {
+		return err
+	}
+	if !bytes.Equal(keyForComparison(spec, key), keyForComparison(spec, p.Key)) {
+		return errors.New("provided key doesn't match proof key")
+	}
+	calc, err := p.Calculate()
+	if err != nil {
+		return fmt.Errorf("error calculating root, %w", err)
+	}
+	if !bytes.Equal(root, calc) {
+		return errors.New("calculcated root doesn't match provided root")
+	}
+	return nil
+}
+
+// CheckAgainstSpec will verify the leaf and all path steps are in the format defined in spec
+func (p *ExclusionProof) CheckAgainstSpec(spec *ProofSpec) error {
+	if p.GetLeaf() == nil {
+		return errors.New("exclusion Proof needs defined LeafOp")
+	}
+
+	// Custom leaf spec validation
+	if p.Leaf.Hash != spec.LeafSpec.Hash {
+		return fmt.Errorf("unexpected HashOp: %d", p.Leaf.Hash)
+	}
+	if p.Leaf.PrehashKey != HashOp_NO_HASH {
+		return errors.New("exclusion proof must have leaf with PrehashKey == NO_HASH")
+	}
+	if p.Leaf.PrehashValue != HashOp_NO_HASH {
+		return errors.New("exclusion proof must have leaf with PrehashValue == NO_HASH")
+	}
+	if p.Leaf.Length != spec.LeafSpec.Length {
+		return fmt.Errorf("unexpected LengthOp: %d", p.Leaf.Length)
+	}
+	if !bytes.HasPrefix(p.Leaf.Prefix, spec.LeafSpec.Prefix) {
+		return fmt.Errorf("leaf Prefix doesn't start with %X", spec.LeafSpec.Prefix)
+	}
+	if spec.MinDepth > 0 && len(p.Path) < int(spec.MinDepth) {
+		return fmt.Errorf("innerOps depth too short: %d", len(p.Path))
+	}
+	if spec.MaxDepth > 0 && len(p.Path) > int(spec.MaxDepth) {
+		return fmt.Errorf("innerOps depth too long: %d", len(p.Path))
+	}
+
+	layerNum := 1
+
+	for _, inner := range p.Path {
+		if err := inner.CheckAgainstSpec(spec, layerNum); err != nil {
+			return fmt.Errorf("inner, %w", err)
+		}
+		layerNum += 1
+	}
+	return nil
+}
+
 // Calculate determines the root hash that matches the given nonexistence rpoog.
 // You must validate the result is what you have in a header.
 // Returns error if the calculations cannot be performed.