How to encrypt private messages so that they cannot be read by the system administrator

Question

I'm not sure if this is the right place, but let's see.

I am developing a system for sending private messages from one user to another user. PHP 5.2.x is running under the hood.

Now I’m looking for a way to encrypt private messages so that I can’t access them . At the moment, I have no idea how to implement such a system where I do not know the encryption key.

My first idea was to combine it with something like OAuth.

A few more requirements to find out the problem:

• Public web page
• good usability

Answer 1

, . javascript.

javascript:

• http://www.ohdave.com/rsa/
• http://www.movable-type.co.uk/scripts/aes.html

, :

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Answer 2

RSA ? http://en.wikipedia.org/wiki/Public-key_cryptography

Answer 3

Diffie-Hellman , .

, , . , , . PHP-, , .

Answer 4

, ?