Encrypt all keys in backup with the same pass phrase #4060
Description
PR #3973 implemented backing up several keys to file or inbox.
The checks included: whether all the keys are encrypted and passphrase strength (for inbox).
If keys are encrypted by different pass phrases, this error is shown:
Your keys are protected with different pass phrases.
Backing them up together isn't supported yet.
So we need to re-encrypt (some) keys to honor the requirement of a single passphrase for all keys as specified in #2482 and remove this error.
Need to design a proper UI for that?
Also note that current message to enter a passphrase Enter your pass phrase to back up may be misleading, as it actually collects passphrases to decrypt keys, rather than re-encrypt them.
UPDATE Also consider limitations imposed by unsolved #956