Unfortunately, I receive a lot more email than I can process in a reasonable amount of time. This means that: (1) my email response time is a lot slower than I would like; and (2) your email might have gotten lost.
Students applying for a PhD. I try my best to reply to emails from prospective graduate students but this is very difficult and often I just cannot keep up. In our department, PhD applicants are reviewed and accepted by a committee so sending me an email will not impact your chances of acceptance. I also cannot give you an estimate of your chances of being accepted. Of course, if you are accepted, I will be happy to meet and discuss possible research projects.
Students interested in internships. My lab does not have any opportunities for non-Brown summer interns; even if you have your own funding.
Brown undergrads interested in research. My lab works with several Brown undergraduates every year but getting on a project can be challenging. The main reason is that cryptography has a high learning curve and it takes a while to acquire the pre-requisites needed to do cryptography research. For this reason most of the undergraduate students we work with are seniors and occasionally juniors. The best way to prepare for doing research with us is to either take CS151 or take my CS2950-v seminar. Many of the research projects we do with undergraduates started out as CS2950-v projects.
Meetings. I spend a huge amount of time in meetings. This means that scheduling a meeting with me can take longer than what you might expect. If you are a Brown student, the quickest way to meet with me is to come to my office hours which are Mondays 3-5 in CIT 507.