diff --git a/cipher.go b/cipher.go
index 2e2c3e9..9a3e946 100644
--- a/cipher.go
+++ b/cipher.go
@@ -35,17 +35,23 @@ const (
 
 // Cipher cipher
 type Cipher struct {
-	cipher C.gnutls_cipher_hd_t
-	t      int
+	cipher    C.gnutls_cipher_hd_t
+	t         int
+	blockSize int
 }
 
 // NewCipher create cipher
 func NewCipher(t int, key []byte, iv []byte) (*Cipher, error) {
-	ivSize := C.cipher_get_block_size(C.int(t))
-	blockSize := C.cipher_get_iv_size(C.int(t))
-	if len(key) != int(blockSize) || len(iv) != int(ivSize) {
+	keysize := GetCipherKeySize(t)
+	ivSize := GetCipherIVSize(t)
+	blocksize := GetCipherBlockSize(t)
+	//log.Printf("block size: %d, iv size: %d", int(ivSize), int(blockSize))
+	if len(key) != int(keysize) {
+		return nil, fmt.Errorf("wrong key size")
+	}
 
-		return nil, fmt.Errorf("wrong block/iv size")
+	if len(iv) != int(ivSize) {
+		return nil, fmt.Errorf("wrong iv size")
 	}
 
 	ckey := C.CBytes(key)
@@ -59,13 +65,12 @@ func NewCipher(t int, key []byte, iv []byte) (*Cipher, error) {
 		log.Println("new cipher return nil")
 		return nil, nil
 	}
-	return &Cipher{c, t}, nil
+	return &Cipher{c, t, blocksize}, nil
 }
 
 // Encrypt encrypt
 func (c *Cipher) Encrypt(buf []byte) ([]byte, error) {
-	blockSize := C.cipher_get_iv_size(C.int(c.t))
-	if len(buf)%int(blockSize) != 0 {
+	if len(buf)%c.blockSize != 0 {
 		return nil, fmt.Errorf("wrong block size")
 	}
 
@@ -86,8 +91,7 @@ func (c *Cipher) Encrypt(buf []byte) ([]byte, error) {
 
 // Decrypt decrypt
 func (c *Cipher) Decrypt(buf []byte) ([]byte, error) {
-	blockSize := C.cipher_get_iv_size(C.int(c.t))
-	if len(buf)%int(blockSize) != 0 {
+	if len(buf)%c.blockSize != 0 {
 		return nil, fmt.Errorf("wrong block size")
 	}
 
@@ -111,3 +115,18 @@ func (c *Cipher) Close() error {
 	C.gnutls_cipher_deinit(c.cipher)
 	return nil
 }
+
+// GetCipherKeySize get the cipher algorithm key length
+func GetCipherKeySize(t int) int {
+	return int(C.gnutls_cipher_get_key_size(C.gnutls_cipher_algorithm_t(t)))
+}
+
+// GetCipherIVSize get the cipher algorithm iv length
+func GetCipherIVSize(t int) int {
+	return int(C.gnutls_cipher_get_iv_size(C.gnutls_cipher_algorithm_t(t)))
+}
+
+// GetCipherBlockSize get the cipher algorithm block size
+func GetCipherBlockSize(t int) int {
+	return int(C.gnutls_cipher_get_block_size(C.gnutls_cipher_algorithm_t(t)))
+}