Encryption and decryption for banking API request response.

Question

Hi 

i am creating a wcf service for banking application, which will consumed by many clients.

i want to know which is the best mechanism for security.

currently i and doing AES encryption and decryption for request and response with some key and my client will also have that key for encyptsion and decryption. is that enough? any other way? or something more need to do? 

anybody has any point on it. please let me know.

 

Thanks