diff --git a/service/signature/data.go b/service/signature/data.go
index f42b06f..00d591e 100644
--- a/service/signature/data.go
+++ b/service/signature/data.go
@@ -8,7 +8,7 @@ import (
 
 type DataSource interface {
 	ReadSignedData([]byte) ([]byte, error)
-	SignedDataLength() int
+	SignedDataSize() int
 }
 
 type DataWithSignature interface {
diff --git a/service/signature/request.go b/service/signature/request.go
index 9dd34a9..fc72be7 100644
--- a/service/signature/request.go
+++ b/service/signature/request.go
@@ -7,8 +7,8 @@ import (
 )
 
 type SignedRequest interface {
-	Body() DataSource
-	MetaHeader() DataSource
+	RequestBody() DataSource
+	RequestMetaHeader() DataSource
 	OriginVerificationHeader() DataSource
 
 	SetBodySignatureWithKey(key, sig []byte)
@@ -27,12 +27,12 @@ func SignRequest(key *ecdsa.PrivateKey, src SignedRequest) error {
 	}
 
 	// sign body
-	if err := SignDataWithHandler(key, src.Body(), src.SetBodySignatureWithKey); err != nil {
+	if err := SignDataWithHandler(key, src.RequestBody(), src.SetBodySignatureWithKey); err != nil {
 		return errors.Wrap(err, "could not sign body")
 	}
 
 	// sign meta
-	if err := SignDataWithHandler(key, src.Body(), src.SetMetaSignatureWithKey); err != nil {
+	if err := SignDataWithHandler(key, src.RequestMetaHeader(), src.SetMetaSignatureWithKey); err != nil {
 		return errors.Wrap(err, "could not sign meta header")
 	}
 
@@ -46,12 +46,12 @@ func SignRequest(key *ecdsa.PrivateKey, src SignedRequest) error {
 
 func VerifyRequest(src SignedRequest) error {
 	// verify body signature
-	if err := VerifyDataWithSource(src.Body(), src.BodySignatureWithKey); err != nil {
+	if err := VerifyDataWithSource(src.RequestBody(), src.BodySignatureWithKey); err != nil {
 		return errors.Wrap(err, "could not verify body")
 	}
 
 	// verify meta header
-	if err := VerifyDataWithSource(src.MetaHeader(), src.MetaSignatureWithKey); err != nil {
+	if err := VerifyDataWithSource(src.RequestMetaHeader(), src.MetaSignatureWithKey); err != nil {
 		return errors.Wrap(err, "could not verify meta header")
 	}
 
diff --git a/service/signature/util.go b/service/signature/util.go
index c86fd00..9033eab 100644
--- a/service/signature/util.go
+++ b/service/signature/util.go
@@ -19,7 +19,7 @@ func dataForSignature(src DataSource) ([]byte, error) {
 
 	buf := bytesPool.Get().([]byte)
 
-	if size := src.SignedDataLength(); size < 0 {
+	if size := src.SignedDataSize(); size < 0 {
 		return nil, errors.New("negative length")
 	} else if size <= cap(buf) {
 		buf = buf[:size]