Why do scientists/cryptographers have to judge ethics for themselves? Not sure what you're asking. Bertrand Russell judged the bomb to be a danger for humanity and chose to express his own views on it.
No one else understands the implications of an experiment or a new methodology. I was at a meeting recently discussing ethics committees for computer science. A medical expert gave his opinion and said (paraphrasing): I fail to see the problem with digitalisation, we have had medical records on paper for years, now they are on a computer, what is the difference?
I don't mean to say that every scientist should do this individually. They should discuss this with colleagues, and with an ethics committee, which should contain subject matter experts, but also ethicists.