Which security artifacts to use for this?

[Ajay Oruganti]

We have to send a string to another app in a confidential manner. The recipient also must know that it came from our app/server.
What is the bestway to do this? As an interim solution, we are doing Symmetric encryption of the string. We are exchanging Base64Encoded keys physically.
Can the security gurus here suggest the 'right way' to do this? What security artifacts would make the perfect solution for this problem?
Thanks,
Ajay

[Jon Eaves]

Generally the approach is encrypted (for the security) and signed (for the authenticity).
Use a public key algorithm and have the two machines authenticate. Of course the actual answer depends heavily on what you're trying to do.