I have to implement something similar to PayPal IPN / Return URL. In my scenario , PayPal Gateway => My Server && Online Store => My Customer
I have to push a very small piece of information through the Return URL in an encrypted format. I would like to generate something like Public Key and Private Key for each customer, and give the Private Key to them. The info will be encrypted using the Public Key at my server and sent via URL.
The developer managing the customer's site would have to use his Private key to decode the information and do some stuff based on that.
Which is the best encryption available on popular languages by default so that the life of the developers at my customer's end is made simpler.