Yes but this is nothing to do with cryptography per se. Most servers can be taken down by a client that finds some expensive operation it can get executed, then

Yes but this is nothing to do with cryptography per se. Most servers can be taken down by a client that finds some expensive operation it can get executed, then sends a bunch of same. The solution implies a generic per-client or per-request resource limit mechanism (which in my experience some systems have, but most do not). This is probably the only good thing about "serverless"/lambda type solutions.