diff --git a/ecdsa.go b/ecdsa.go
index 42c5cf1..2a5279e 100644
--- a/ecdsa.go
+++ b/ecdsa.go
@@ -63,7 +63,7 @@ func (pr EcdsaPrivateKey) Sign(message []byte, hash crypto.Hash) ([]byte, error)
 }
 
 // get the private key
-func (pr EcdsaPrivateKey) privateKey() crypto.PrivateKey {
+func (pr EcdsaPrivateKey) PrivateKey() crypto.PrivateKey {
   return pr.private_key
 }
 
diff --git a/rsa.go b/rsa.go
index 410b9f7..ac649b7 100644
--- a/rsa.go
+++ b/rsa.go
@@ -46,7 +46,7 @@ func (pr RsaPrivateKey) Sign(message []byte, hash crypto.Hash) ([]byte, error) {
 }
 
 // get the private key
-func (pr RsaPrivateKey) privateKey() crypto.PrivateKey {
+func (pr RsaPrivateKey) PrivateKey() crypto.PrivateKey {
   return pr.private_key
 }
 
diff --git a/types.go b/types.go
index 22c35d4..c2a4599 100644
--- a/types.go
+++ b/types.go
@@ -20,7 +20,7 @@ type (
     Sign(message []byte, hash crypto.Hash) ([]byte, error)
 
     // return the private key structure
-    privateKey() crypto.PrivateKey
+    PrivateKey() crypto.PrivateKey
   }
 
   // interface for any public key