diff --git a/les/odr_requests.go b/les/odr_requests.go
index c7f06df94d..075fcd92ca 100644
--- a/les/odr_requests.go
+++ b/les/odr_requests.go
@@ -230,7 +230,7 @@ func (r *TrieRequest) Validate(db ethdb.Database, msg *Msg) error {
 		}
 		nodeSet := proofs[0].NodeSet()
 		// Verify the proof and store if checks out
-		if _, err, _ := trie.VerifyProof(r.Id.Root, r.Key, nodeSet); err != nil {
+		if _, _, err := trie.VerifyProof(r.Id.Root, r.Key, nodeSet); err != nil {
 			return fmt.Errorf("merkle proof verification failed: %v", err)
 		}
 		r.Proof = nodeSet
@@ -241,7 +241,7 @@ func (r *TrieRequest) Validate(db ethdb.Database, msg *Msg) error {
 		// Verify the proof and store if checks out
 		nodeSet := proofs.NodeSet()
 		reads := &readTraceDB{db: nodeSet}
-		if _, err, _ := trie.VerifyProof(r.Id.Root, r.Key, reads); err != nil {
+		if _, _, err := trie.VerifyProof(r.Id.Root, r.Key, reads); err != nil {
 			return fmt.Errorf("merkle proof verification failed: %v", err)
 		}
 		// check if all nodes have been read by VerifyProof
@@ -400,7 +400,7 @@ func (r *ChtRequest) Validate(db ethdb.Database, msg *Msg) error {
 		var encNumber [8]byte
 		binary.BigEndian.PutUint64(encNumber[:], r.BlockNum)
 
-		value, err, _ := trie.VerifyProof(r.ChtRoot, encNumber[:], light.NodeList(proof.Proof).NodeSet())
+		value, _, err := trie.VerifyProof(r.ChtRoot, encNumber[:], light.NodeList(proof.Proof).NodeSet())
 		if err != nil {
 			return err
 		}
@@ -435,7 +435,7 @@ func (r *ChtRequest) Validate(db ethdb.Database, msg *Msg) error {
 		binary.BigEndian.PutUint64(encNumber[:], r.BlockNum)
 
 		reads := &readTraceDB{db: nodeSet}
-		value, err, _ := trie.VerifyProof(r.ChtRoot, encNumber[:], reads)
+		value, _, err := trie.VerifyProof(r.ChtRoot, encNumber[:], reads)
 		if err != nil {
 			return fmt.Errorf("merkle proof verification failed: %v", err)
 		}
@@ -529,7 +529,7 @@ func (r *BloomRequest) Validate(db ethdb.Database, msg *Msg) error {
 
 	for i, idx := range r.SectionIdxList {
 		binary.BigEndian.PutUint64(encNumber[2:], idx)
-		value, err, _ := trie.VerifyProof(r.BloomTrieRoot, encNumber[:], reads)
+		value, _, err := trie.VerifyProof(r.BloomTrieRoot, encNumber[:], reads)
 		if err != nil {
 			return err
 		}
diff --git a/trie/iterator.go b/trie/iterator.go
index 3bae8e186b..64110c6d96 100644
--- a/trie/iterator.go
+++ b/trie/iterator.go
@@ -99,8 +99,8 @@ type nodeIterator struct {
 	err   error                // Failure set in case of an internal error in the iterator
 }
 
-// iteratorEnd is stored in nodeIterator.err when iteration is done.
-var iteratorEnd = errors.New("end of iteration")
+// errIteratorEnd is stored in nodeIterator.err when iteration is done.
+var errIteratorEnd = errors.New("end of iteration")
 
 // seekError is stored in nodeIterator.err if the initial seek has failed.
 type seekError struct {
@@ -162,7 +162,7 @@ func (it *nodeIterator) Path() []byte {
 }
 
 func (it *nodeIterator) Error() error {
-	if it.err == iteratorEnd {
+	if it.err == errIteratorEnd {
 		return nil
 	}
 	if seek, ok := it.err.(seekError); ok {
@@ -176,7 +176,7 @@ func (it *nodeIterator) Error() error {
 // sets the Error field to the encountered failure. If `descend` is false,
 // skips iterating over any subnodes of the current node.
 func (it *nodeIterator) Next(descend bool) bool {
-	if it.err == iteratorEnd {
+	if it.err == errIteratorEnd {
 		return false
 	}
 	if seek, ok := it.err.(seekError); ok {
@@ -201,8 +201,8 @@ func (it *nodeIterator) seek(prefix []byte) error {
 	// Move forward until we're just before the closest match to key.
 	for {
 		state, parentIndex, path, err := it.peek(bytes.HasPrefix(key, it.path))
-		if err == iteratorEnd {
-			return iteratorEnd
+		if err == errIteratorEnd {
+			return errIteratorEnd
 		} else if err != nil {
 			return seekError{prefix, err}
 		} else if bytes.Compare(path, key) >= 0 {
@@ -246,7 +246,7 @@ func (it *nodeIterator) peek(descend bool) (*nodeIteratorState, *int, []byte, er
 		// No more child nodes, move back up.
 		it.pop()
 	}
-	return nil, nil, nil, iteratorEnd
+	return nil, nil, nil, errIteratorEnd
 }
 
 func (st *nodeIteratorState) resolve(tr *Trie, path []byte) error {
diff --git a/trie/proof.go b/trie/proof.go
index 508e4a6cf4..6cb8f4d5f7 100644
--- a/trie/proof.go
+++ b/trie/proof.go
@@ -102,28 +102,28 @@ func (t *SecureTrie) Prove(key []byte, fromLevel uint, proofDb ethdb.Putter) err
 // VerifyProof checks merkle proofs. The given proof must contain the value for
 // key in a trie with the given root hash. VerifyProof returns an error if the
 // proof contains invalid trie nodes or the wrong value.
-func VerifyProof(rootHash common.Hash, key []byte, proofDb DatabaseReader) (value []byte, err error, nodes int) {
+func VerifyProof(rootHash common.Hash, key []byte, proofDb DatabaseReader) (value []byte, nodes int, err error) {
 	key = keybytesToHex(key)
 	wantHash := rootHash
 	for i := 0; ; i++ {
 		buf, _ := proofDb.Get(wantHash[:])
 		if buf == nil {
-			return nil, fmt.Errorf("proof node %d (hash %064x) missing", i, wantHash), i
+			return nil, i, fmt.Errorf("proof node %d (hash %064x) missing", i, wantHash)
 		}
 		n, err := decodeNode(wantHash[:], buf, 0)
 		if err != nil {
-			return nil, fmt.Errorf("bad proof node %d: %v", i, err), i
+			return nil, i, fmt.Errorf("bad proof node %d: %v", i, err)
 		}
 		keyrest, cld := get(n, key)
 		switch cld := cld.(type) {
 		case nil:
 			// The trie doesn't contain the key.
-			return nil, nil, i
+			return nil, i, nil
 		case hashNode:
 			key = keyrest
 			copy(wantHash[:], cld)
 		case valueNode:
-			return cld, nil, i + 1
+			return cld, i + 1, nil
 		}
 	}
 }
diff --git a/trie/proof_test.go b/trie/proof_test.go
index a3537787cc..dee6f7d859 100644
--- a/trie/proof_test.go
+++ b/trie/proof_test.go
@@ -40,7 +40,7 @@ func TestProof(t *testing.T) {
 		if trie.Prove(kv.k, 0, proofs) != nil {
 			t.Fatalf("missing key %x while constructing proof", kv.k)
 		}
-		val, err, _ := VerifyProof(root, kv.k, proofs)
+		val, _, err := VerifyProof(root, kv.k, proofs)
 		if err != nil {
 			t.Fatalf("VerifyProof error for key %x: %v\nraw proof: %v", kv.k, err, proofs)
 		}
@@ -58,7 +58,7 @@ func TestOneElementProof(t *testing.T) {
 	if len(proofs.Keys()) != 1 {
 		t.Error("proof should have one element")
 	}
-	val, err, _ := VerifyProof(trie.Hash(), []byte("k"), proofs)
+	val, _, err := VerifyProof(trie.Hash(), []byte("k"), proofs)
 	if err != nil {
 		t.Fatalf("VerifyProof error: %v\nproof hashes: %v", err, proofs.Keys())
 	}
@@ -82,7 +82,7 @@ func TestVerifyBadProof(t *testing.T) {
 		proofs.Delete(key)
 		mutateByte(node)
 		proofs.Put(crypto.Keccak256(node), node)
-		if _, err, _ := VerifyProof(root, kv.k, proofs); err == nil {
+		if _, _, err := VerifyProof(root, kv.k, proofs); err == nil {
 			t.Fatalf("expected proof to fail for key %x", kv.k)
 		}
 	}
@@ -131,7 +131,7 @@ func BenchmarkVerifyProof(b *testing.B) {
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		im := i % len(keys)
-		if _, err, _ := VerifyProof(root, []byte(keys[im]), proofs[im]); err != nil {
+		if _, _, err := VerifyProof(root, []byte(keys[im]), proofs[im]); err != nil {
 			b.Fatalf("key %x: %v", keys[im], err)
 		}
 	}
diff --git a/trie/secure_trie.go b/trie/secure_trie.go
index 3881ee18a0..6a50cfd5a6 100644
--- a/trie/secure_trie.go
+++ b/trie/secure_trie.go
@@ -155,14 +155,19 @@ func (t *SecureTrie) Commit(onleaf LeafCallback) (root common.Hash, err error) {
 	return t.trie.Commit(onleaf)
 }
 
+// Hash returns the root hash of SecureTrie. It does not write to the
+// database and can be used even if the trie doesn't have one.
 func (t *SecureTrie) Hash() common.Hash {
 	return t.trie.Hash()
 }
 
+// Root returns the root hash of SecureTrie.
+// Deprecated: use Hash instead.
 func (t *SecureTrie) Root() []byte {
 	return t.trie.Root()
 }
 
+// Copy returns a copy of SecureTrie.
 func (t *SecureTrie) Copy() *SecureTrie {
 	cpy := *t
 	return &cpy