Encrpytion between iPhone and a php page with Key exchange

I need to send data to and from a php-page from my iPhone application and now I have a couple of questions to get it right the first time, and the best result:)

Lets start with the transfer of data. Which is the best way to get the data from a php-page?

Option 1: Use NSString in a background thread

[[NSString allo开发者_运维问答c] initWithContentsOfURL:url];

Or Option 2: Use NSURLConnection with delegates?

Then we have the encryption part. I have google a little bit but haven't found so much. I need to be able to encrypt and decrypt on both sides (both in the iPhone app and on the php-page). What encryption is best for this? Are there any implementations of any good encryption?

And last, for key-exchange. I thinking of using diffie-hellman, which "require" large prime-numbers. Are there any easy way to generate such thing (on both the iPhone and the php-page)?

Have you considered using HTTPS? SSL/TLS seems to match what you're looking for in terms of encryption, key exchange, etc. HTTP on top of this will get you to transfer data to the PHP page.