diff --git a/dkim.go b/dkim.go
index b0278f0..6c0f061 100644
--- a/dkim.go
+++ b/dkim.go
@@ -11,12 +11,10 @@ import (
 	"crypto/x509"
 	"encoding/base64"
 	"encoding/pem"
-	//"fmt"
 	"hash"
 	"io/ioutil"
 	"regexp"
 	"strings"
-	//"time"
 )
 
 const (
@@ -89,7 +87,6 @@ func NewSigOptions() sigOptions {
 // Sign signs an email
 func Sign(email *bytes.Reader, options sigOptions) (*bytes.Reader, error) {
 	var privateKey *rsa.PrivateKey
-	// check && sanitize config
 
 	// PrivateKey (required & TODO: valid)
 	if options.PrivateKey == "" {
@@ -99,7 +96,7 @@ func Sign(email *bytes.Reader, options sigOptions) (*bytes.Reader, error) {
 	d, _ := pem.Decode([]byte(options.PrivateKey))
 	key, err := x509.ParsePKCS1PrivateKey(d.Bytes)
 	if err != nil {
-		return nil, err
+		return nil, ErrCandNotParsePrivateKey
 	}
 	privateKey = key
 
@@ -237,8 +234,7 @@ func canonicalize(emailReader *bytes.Reader, options sigOptions) (headers, body
 		return
 	}
 
-	//fmt.Println(email)
-	// todo \n -> \r\n
+	// TODO: \n -> \r\n
 	parts := bytes.SplitN(email, []byte{13, 10, 13, 10}, 2)
 
 	if len(parts) != 2 {
diff --git a/dkimHeader.go b/dkimHeader.go
index 41613c7..bf50303 100644
--- a/dkimHeader.go
+++ b/dkimHeader.go
@@ -206,7 +206,7 @@ func NewDkimHeaderBySigOptions(options sigOptions) *DkimHeader {
 }
 
 // GetHeaderBase return base header for signers
-// Todo: some refactoring...
+// Todo: some refactoring needed...
 func (d *DkimHeader) GetHeaderBase(bodyHash string) string {
 	h := "DKIM-Signature: v=" + d.Version + "; a=" + d.Algorithm + "; q=" + strings.Join(d.QueryMethods, ":") + "; c=" + d.MessageCanonicalization + ";" + CRLF + TAB
 	subh := "s=" + d.Selector + ";"
@@ -298,5 +298,3 @@ func (d *DkimHeader) GetHeaderBase(bodyHash string) string {
 	h += subh + ";" + FWS + "b="
 	return h
 }
-
-//'test._domainkey.tmail.io:v=DKIM1;k=rsa;s=email;h=sha256;t=y;p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDNUXO+Qsl1tw+GjrqFajz0ERSEUs1FHSL/+udZRWn1Atw8gz0+tcGqhWChBDeU9gY5sKLEAZnX3FjC/T/IbqeiSM68kS5vLkzRI84eiJrm3+IieUqIIicsO+WYxQs+JgVx5XhpPjX4SQjHtwEC2xKkWnEv+VPgO1JWdooURcSC6QIDAQAB':300::
diff --git a/errors.go b/errors.go
index 0dd2129..5920a05 100644
--- a/errors.go
+++ b/errors.go
@@ -20,6 +20,9 @@ var (
 	// If bad Canonicalization parameter
 	ErrSignBadCanonicalization = errors.New("bad Canonicalization parameter")
 
+	// when unable to parse private key
+	ErrCandNotParsePrivateKey = errors.New("can not parse private key, check format (pem) and validity")
+
 	// Bad algorithm
 	ErrSignBadAlgo = errors.New("bad algorithm. Only rsa-sha1 or rsa-sha256 are permitted")