diff --git a/client/coniksclient/internal/cmd/register.go b/client/coniksclient/internal/cmd/register.go
index 762d3bc..067a0fa 100644
--- a/client/coniksclient/internal/cmd/register.go
+++ b/client/coniksclient/internal/cmd/register.go
@@ -75,14 +75,14 @@ Example call:
 		case p.CheckBindingsDiffer:
 			switch response.Error {
 			case p.ReqNameExisted:
-				fmt.Println(`Are you trying to update your binding? Unfortunately, KeyChange hasn't been supported yet.`)
+				fmt.Println(`Are you trying to update your binding? Unfortunately, KeyChange isn't supported yet.`)
 			case p.ReqSuccess:
-				fmt.Println("Oops! Probably the server is trying to sneak in some other key.")
+				fmt.Println("Oops! The server snuck in some other key.")
 				recvKey, err := response.GetKey()
 				if err != nil {
 					fmt.Println("Cannot get the key from the response, error: " + err.Error())
 				}
-				fmt.Println("You got [" + string(recvKey) + "] instead of [" + string(key) + "]")
+				fmt.Println("[" + string(recvKey) + "] was registered instead of [" + string(key) + "]")
 			}
 		default:
 			fmt.Println("Error: " + err.Error())
diff --git a/merkletree/proof.go b/merkletree/proof.go
index 9471f03..49e2564 100644
--- a/merkletree/proof.go
+++ b/merkletree/proof.go
@@ -80,21 +80,25 @@ func (ap *AuthenticationPath) authPathHash() []byte {
 	return hash
 }
 
-// VerifyBinding verifies both the value and the commitment
-// of the proof node of the authentication path.
-//
-// This should be called only when ap is a proof of inclusion.
+// VerifyBinding verifies the value of the proof node
+// of the authentication path. It also verifies the commitment
+// of the proof node if ap is a proof of inclusion.
 func (ap *AuthenticationPath) VerifyBinding(key, value []byte) bool {
-	return bytes.Equal(ap.Leaf.Value, value) &&
-		ap.Leaf.Commitment.Verify(key, value)
+	return (ap.ProofType() == ProofOfAbsence && ap.Leaf.Value == nil) ||
+		(bytes.Equal(ap.Leaf.Value, value) && ap.Leaf.Commitment.Verify(key, value))
 }
 
-// VerifyIndex checks if the private index of the proof node and
-// the lookup index match in the first l bits with l is the Level
-// of the proof node.
+// VerifyIndex verifies the private index of the proof node.
+//
+// If the proof is a proof of absence, it checks if the index
+// of the proof node and the lookup index match in the first
+// l bits with l is the Level of the proof node.
 //
-// This should be called only when ap is a proof of absence.
+// If the proof is a proof of inclusion, it returns true immediately.
 func (ap *AuthenticationPath) VerifyIndex() bool {
+	if ap.ProofType() == ProofOfInclusion {
+		return true
+	}
 	// Check if i and j match in the first l bits
 	indexBits := utils.ToBits(ap.Leaf.Index)
 	lookupIndexBits := utils.ToBits(ap.LookupIndex)
@@ -114,19 +118,6 @@ func (ap *AuthenticationPath) VerifySTR(treeHash []byte) bool {
 	return bytes.Equal(treeHash, ap.authPathHash())
 }
 
-// Verify combines VerifyBinding(), VerifyIndex(), and VerifySTR(),
-// and abstracts away the detail of the failure.
-// This should be called after the VRF index is verified successfully.
-func (ap *AuthenticationPath) Verify(key, value, treeHash []byte) bool {
-	switch {
-	case ap.ProofType() == ProofOfAbsence && ap.VerifyIndex(),
-		ap.ProofType() == ProofOfInclusion && ap.VerifyBinding(key, value):
-		return ap.VerifySTR(treeHash)
-	default:
-		return false
-	}
-}
-
 func (ap *AuthenticationPath) ProofType() ProofType {
 	if ap.proofType == undeterminedProof {
 		if bytes.Equal(ap.LookupIndex, ap.Leaf.Index) {
diff --git a/merkletree/proof_test.go b/merkletree/proof_test.go
index b71aa9e..8908478 100644
--- a/merkletree/proof_test.go
+++ b/merkletree/proof_test.go
@@ -7,6 +7,16 @@ import (
 	"github.com/coniks-sys/coniks-go/utils"
 )
 
+func verifyAuthPath(ap *AuthenticationPath, key, value []byte, treehash []byte) bool {
+	if !ap.VerifyIndex() {
+		return false
+	}
+	if !ap.VerifyBinding(key, value) {
+		return false
+	}
+	return ap.VerifySTR(treehash)
+}
+
 func TestVerifyProof(t *testing.T) {
 	m, err := NewMerkleTree()
 	if err != nil {
@@ -63,7 +73,7 @@ func TestVerifyProof(t *testing.T) {
 		t.Fatal("Expect a proof of inclusion")
 	}
 	// verify auth path
-	if !proof.Verify([]byte(key3), val3, m.hash) {
+	if !verifyAuthPath(proof, []byte(key3), val3, m.hash) {
 		t.Error("Proof of inclusion verification failed.")
 	}
 
@@ -78,7 +88,7 @@ func TestVerifyProof(t *testing.T) {
 		!bytes.Equal(vrfPrivKey1.Compute([]byte("123")), proof.LookupIndex) {
 		t.Fatal("Expect a proof of absence")
 	}
-	if !proof.Verify([]byte("123"), nil, m.hash) {
+	if !verifyAuthPath(proof, []byte("123"), nil, m.hash) {
 		t.Error("Proof of absence verification failed.")
 	}
 }
@@ -111,7 +121,7 @@ func TestVerifyProofSamePrefix(t *testing.T) {
 		utils.ToBytes(utils.ToBits(absentIndex)[:proof.Leaf.Level])) {
 		t.Fatal("Expect these indices share the same prefix in the first bit")
 	}
-	if !proof.Verify([]byte("a"), nil, m.hash) {
+	if !verifyAuthPath(proof, []byte("a"), nil, m.hash) {
 		t.Error("Proof of absence verification failed.")
 	}
 
@@ -128,7 +138,7 @@ func TestVerifyProofSamePrefix(t *testing.T) {
 		t.Fatal("Expect a proof of inclusion")
 	}
 	// step 2. verify auth path
-	if !proof.Verify([]byte(key1), val1, m.hash) {
+	if !verifyAuthPath(proof, []byte(key1), val1, m.hash) {
 		t.Error("Proof of inclusion verification failed.")
 	}
 }
diff --git a/protocol/consistencychecks.go b/protocol/consistencychecks.go
index 3265235..25a56d3 100644
--- a/protocol/consistencychecks.go
+++ b/protocol/consistencychecks.go
@@ -218,25 +218,16 @@ func verifyAuthPath(uname string, key []byte,
 		return CheckBadVRFProof
 	}
 
-	if key == nil {
-		// key is nil when the user does lookup for the first time.
-		// Accept the received key as TOFU
-		key = ap.Leaf.Value
+	if !ap.VerifyIndex() {
+		return CheckBadLookupIndex
 	}
-
-	if ap.ProofType() == m.ProofOfAbsence {
-		if !ap.VerifyIndex() {
-			return CheckBadLookupIndex
-		}
-	} else {
-		if !ap.VerifyBinding([]byte(uname), key) {
-			return CheckBindingsDiffer
-		}
+	if key != nil && !ap.VerifyBinding([]byte(uname), key) {
+		return CheckBindingsDiffer
 	}
-	if ap.VerifySTR(str.TreeHash) {
-		return nil
+	if !ap.VerifySTR(str.TreeHash) {
+		return CheckBadAuthPath
 	}
-	return CheckBadAuthPath
+	return nil
 }
 
 func (cc *ConsistencyChecks) updateTBs(requestType int, msg *Response,