The `relay_digest_matches()` is used in `relay_crypt()` and it is called for a huge portion of cells that come through the relay. Roughly speaking, if a relay is at 10MB/s and with cells of size 514 bytes, we are talking about a bit less than 20k cells *per* second meaning more than a million `tor_malloc(20)` per minute. This is the place: ``` backup_digest = crypto_digest_dup(digest); ``` I think we should find a way to avoid this especially in the fast path of tor in order to avoid memory fragmentation as much as possible. We could either use the stack, a static value or `memarea` subsystem.