What to answer an author asking me if I reviewed his/her paper? Suppose I review someone's paper anonymously, the paper gets accepted, and a year or two later we meet e.g. in a social event and he/she asks me "did you review my paper?". What should I answer? There are several sub-questions here:


Suppose the review was a good one, and the paper eventualy got accepted, so I do not mind telling that I was the reviewer. Is there any rule/norm prohibiting me from telling the truth?
Suppose the review was not so good, so I do not want to reveal. What can I answer? If I just say "I am not allowed to tell you", this immediately reveals me... On the other hand, I do not want to lie. What options do I have?
You could say something like


  "I am not in the habit of telling people whether I did or did not review their papers, sorry"


or


  "I don't feel comfortable answering this question."


Or you could defuse the question with a humorous answer, e.g.


  "I would tell you but then I'd have to kill you"


or


  "I don't remember, I always take an amnesia pill immediately after reviewing a paper"


or some similar kind of obviously nonserious smart-assery. None of these answers provide any useful information to the asker, and all of them convey some level of disapproval on your part at being asked, making it unlikely that the asker would press the case any further.