Add an option to in-place decrypt with `ChaCha20Poly1305`

In the next commit we'll use this to avoid an allocation when
deserializing messages from the wire.

diff --git a/lightning/src/util/chacha20poly1305rfc.rs b/lightning/src/util/chacha20poly1305rfc.rs
index a5bec2c82b8cf00da2a597d3c68026aa7e87152f..d5792e0ac2b35f28bc8a90d43217d1874cd0e3ce 100644 (file)
--- a/lightning/src/util/chacha20poly1305rfc.rs
+++ b/lightning/src/util/chacha20poly1305rfc.rs
@@ -122,10 +122,15 @@ mod real_chachapoly {
                        }
                }
 
-               // Decrypt in place, without checking the tag. Use `finish_and_check_tag` to check it
-               // later when decryption finishes.
-               //
-               // Should never be `pub` because the public API should always enforce tag checking.
+               pub fn check_decrypt_in_place(&mut self, input_output: &mut [u8], tag: &[u8]) -> Result<(), ()> {
+                       self.decrypt_in_place(input_output);
+                       if self.finish_and_check_tag(tag) { Ok(()) } else { Err(()) }
+               }
+
+               /// Decrypt in place, without checking the tag. Use `finish_and_check_tag` to check it
+               /// later when decryption finishes.
+               ///
+               /// Should never be `pub` because the public API should always enforce tag checking.
                pub(super) fn decrypt_in_place(&mut self, input_output: &mut [u8]) {
                        debug_assert!(self.finished == false);
                        self.mac.input(input_output);
@@ -133,8 +138,8 @@ mod real_chachapoly {
                        self.cipher.process_in_place(input_output);
                }
 
-               // If we were previously decrypting with `decrypt_in_place`, this method must be used to finish
-               // decrypting and check the tag. Returns whether or not the tag is valid.
+               /// If we were previously decrypting with `just_decrypt_in_place`, this method must be used
+               /// to check the tag. Returns whether or not the tag is valid.
                pub(super) fn finish_and_check_tag(&mut self, tag: &[u8]) -> bool {
                        debug_assert!(self.finished == false);
                        self.finished = true;
@@ -313,6 +318,11 @@ mod fuzzy_chachapoly {
                        true
                }
 
+               pub fn check_decrypt_in_place(&mut self, input_output: &mut [u8], tag: &[u8]) -> Result<(), ()> {
+                       self.decrypt_in_place(input_output);
+                       if self.finish_and_check_tag(tag) { Ok(()) } else { Err(()) }
+               }
+
                pub(super) fn decrypt_in_place(&mut self, _input: &mut [u8]) {
                        assert!(self.finished == false);
                }