Securely send / retrieve data

I would like to be able to send and receive data in a semi-secure manner without using HTTPS or SSL.

I am currently sending data to the server using a salty MD5 hash digest (so as to prevent argument falsification):

http://www.myserver.com?name=John&digest=ed076287532e86365e841e92bfc50d8c

But I would also like to encrypt plain text data on the client, and then decrypt it on the server back into plain text, so that the data looks something like this:

http://www.myserver.com?name=sK5E4Ld4sw5ie&digest=ed076287532e86365e841e92bfc50d8c

What a good way to use for this?