add support for signing for rsa

This adds finally support to sign and verify messages using an RSA
private and public key.
The method used is PKCS1v15, as it was the easiest to implement first.
There is also PSS available in go, so that could be implemented later.

1 files changed, 12 insertions, 2 deletions

diff --git a/rsa.go b/rsa.go
index 6622887..76296ed 100644
--- a/rsa.go
+++ b/rsa.go
@@ -47,7 +47,12 @@ func (pr *RsaPrivateKey) Public() PublicKey {
 }
 
 func (pr RsaPrivateKey) Sign(message []byte, hash crypto.Hash) ([]byte, error) {
-	return make([]byte, 0), errors.New("not implemented yet!")
+	if !hash.Available() {
+		return make([]byte, 0), errors.New("Hash method is not available!")
+	}
+	hashed_message := hash.New()
+	hashed_message.Write(message)
+	return rsa.SignPKCS1v15(rand.Reader, pr.private_key, hash, hashed_message.Sum(nil))
 }
 
 // get the private key
@@ -84,5 +89,10 @@ func (pu *RsaPublicKey) MarshalPem() (io.WriterTo, error) {
 
 // verify a message with a signature using the public key
 func (pu *RsaPublicKey) Verify(message []byte, signature []byte, hash crypto.Hash) (bool, error) {
-	return false, errors.New("not implemented yet!")
+	hashed_message := hash.New()
+	hashed_message.Write(message)
+	if err := rsa.VerifyPKCS1v15(pu.public_key, hash, hashed_message.Sum(nil), signature); err != nil {
+		return false, err
+	}
+	return true, nil
 }