There is a lot of research in this area. Here is a paper on how to search on encrypted data: http://www.cs.berkeley.edu/~dawnsong/papers/se.pdf http://www.cs.b

There is a lot of research in this area. Here is a paper on how to search on encrypted data: http://www.cs.berkeley.edu/~dawnsong/papers/se.pdf http://www.cs.berkeley.edu/~dawnsong/papers/se.pdf One thing you need to be wary of is plaintext attacks. Even if you use a salt and a difficult has but I send you an e-mail and know the contents and can obtain the ciphertext or its digests, you are vulnerable. There are ways past this, of course, but it is one example of a valid attack. The pdf I referenced has what seems to be a pretty workable approach to me and lets you do hidden searches, boolean searches, phrases, proximity queries, etc.