dbcheck should notice that the RSA key stored for new BackupKey encryptions is not 2048 bits, and remove (possibly re-generate) that key.
This would avoid bugs like 11538, where the upgraded domain still didn't work.
To be clear, the steps required are here:
The hard part will be parsing the key from the python code in dbcheck, we will probably need a re-factor
(In reply to Andrew Bartlett from comment #2)
Andrew, are you sure we'll never need the private key again?
I'd avoid to automatically delete private keys.
My sloppy language disguised the fact that I don't want to remove the key, but the CN=BCKUPKEY_PREFERRED Secret pointer to the key. The key remains (and is indeed still required do decrypt an old backup) but should not be used again for new encryptions.
*** This bug has been marked as a duplicate of bug 11285 ***