I set up tarsnap to backup one of my small small cloud servers.   Some notes on the hick-ups:

1. Tarsnap’s install involves compiling it – that tells you about the overall tone :).  The compile requires this include file: “ext2fs/ext2_fs.h”.  My little server lacked that.  It took a while to find how to get it.  In this case the answer was: yum install e2fsprogs-devel
2. There are two keys.  One is used to access your account on his server.  The second is used to encrypt etc. your backups.  I was puzzled about this file since I’d assumed it would encrypt the backups with one key (which would be installed on the machine(s) you backing up), and then a second key (the private key) would be used to decrypt them later.  Turns out the behavior is – sort of – optional.  The 2nd key you get fills both roles, and you need to use the key management tool if you want to make this distinction.