I am making a program like yelp. Some people have some accounts. So I got to send the password to the web.
Should I encrypt the password before sending it?
After that what would be the standard password policy others used?
Should the encrypted password be the one stored on the mySQL serve? In other word, there is absolutely no need for decryption?
Basically it’s like What encryption procedure I must use to send encrypted 'email' and 'password' values over the HTTP protocoll? but for objective-c
After the user logged in, my program need to tell the server that the user is authenticated already. Does my program need to keep sending password?
There are more than one architecture you can implement, and you have to choose considering many factors, like performance, how many users, server architecture…
Basically, you must use https and not http, store hashed password (MD5, SHA, ecc.) and always check if hashed password is equal to stored hashed password.
You can implement also a “session” using token (you have to create a kind of API server side and then use it on client side) or pass username and password in each call to web service (web service must verify credentials every time is called).
Another “fast” (it’s not so fast anyway) solution is to implement (both server-client) a standard protocol like (it’s my favorite) oAuth 2. It’s used by twitter and Facebook, you can learn more here: http://oauth.net/2/