Add errPrivateKeySizeZero for checking private key size

Author: xin-tsla

src/crypto/rsa/pkcs1v15.go

@@ -292,6 +292,9 @@ func SignPKCS1v15(random io.Reader, priv *PrivateKey, hash crypto.Hash, hashed [
 
 tLen := len(prefix) + hashLen
 k := priv.Size()
+if k == 0 {
+return nil, errPrivateKeySizeZero
+}
 if k < tLen+11 {
 return nil, ErrMessageTooLong
 }

src/crypto/rsa/rsa.go

@@ -90,6 +90,7 @@ var (
 errPublicExponentSmall = errors.New("crypto/rsa: public exponent too small")
 errPublicExponentLarge = errors.New("crypto/rsa: public exponent too large")
 errPublicKeySizeZero = errors.New("crypto/rsa: public key size zero")
+errPrivateKeySizeZero = errors.New("crypto/rsa: private key size zero")
 )
 
 // checkPub sanity checks the public key before we use it.