I was referencing the below, but it looks like this is Symmetric encryption vs. assymetric
This may be fine as Kentico holds the "Key" for the symmetric encryption, so that doesn't get exposed, but it does mean that theoretically if someone gets the token and has a kentico installation they can decrypt it themselves.
You would have to implement your own Asymmetric encryption algorithm and class that you could create the public/private key. I don't see anything built into Kentico i'm afriad :(
Another option though, is if you are just looking to pass data between your two sites, if they use the same database you can store the information there and just pass a GUID to that record, OR if they are on different databases but you the databases can 'see' each other, you can create a sql database link and direct query the other database from the first.
Likewise, you can use the ConnectionHelper.GetConnection and pass the other database's connection information so you can query from the other database, and again just pass a GUID. This way only the row GUID is visible and means nothing to any spys.