We referred this link to encrypt a file using AES algo: http://www.example-code.com/objc/crypt_aes_encrypt_file.asp
Here hardcoded keyHex and ivHex are used to encrypt a file.
Now I have couple of related questions
The GenRandomBytesENC method can be called to generate N random bytes and return them as an encoded string (using Base64, hex, etc.)
A typical way of having a shared secret (i.e. a shared symmetric key where only the two parties know the key) is via RSA. See this: http://www.example-code.com/objc/rsa_keyExchange.asp