pkg/cryptstate: add NULL crypto mode.

pkg/cryptstate/mode_null.go

@@ -0,0 +1,38 @@
+// Copyright (c) 2012 The Grumble Authors
+// The use of this source code is goverened by a BSD-style
+// license that can be found in the LICENSE-file.
+
+package cryptstate
+
+// nullMode implements the NULL CryptoMode
+type nullMode struct {}
+
+// NonceSize returns the nonce size to be used with NULL.
+func (n *nullMode) NonceSize() int {
+	return 1
+}
+
+// KeySize returns the key size to be used with NULL.
+func (n *nullMode) KeySize() int {
+	return 0
+}
+
+// Overhead returns the overhead that a ciphertext has over a plaintext.
+func (n *nullMode) Overhead() int {
+	return 0
+}
+
+// SetKey sets a new key. The key must have a length equal to KeySize().
+func (n *nullMode) SetKey(key []byte) {
+}
+
+// Encrypt encrypts a message using NULL and outputs it to dst.
+func (n *nullMode) Encrypt(dst []byte, src []byte, nonce []byte) {
+	copy(dst, src)
+}
+
+// Decrypt decrypts a message using NULL and outputs it to dst.
+func (n *nullMode) Decrypt(dst []byte, src []byte, nonce []byte) bool {
+	copy(dst, src)
+	return true
+}