OK. Your keyring(s) are stored in $HOME/.gnome2/keyrings.
So, the obvious way to sync your keyrings across machines is... just mark that folder as a synced folder with U1. No APIs required!
That will, of course, sync all your keyrings, though, which I believe you don't want to do. So, the next step is this:
- create your keyring, which will be in its own file,
- Create a folder somewhere for your app --
- place a symlink in
~/.gnome2/keyrings/ pointing to
~/.local/share/yourapp/keyrings as a synced folder with Ubuntu One.
That should do what you want! As noted by RAOF, the keyring file is encrypted, so syncing it to U1 is no security risk. No APIs needed.
If you want to do this programmatically -- that is, your app has a "Sync my app's keyring" checkbox which turns this feature on and off -- then you will, of course, need to detect U1, and lead the user through signing up if they want to sync but don't yet have a U1 account. For this, use, from Python, ubuntuone.platform.tools.SyncDaemonTool which gives you full control over the Ubuntu One syncdaemon.