Hello there, craigleech,
We're unable to share the encryption process of importing the bank transactions. It's a process between the bank and QuickBooks.
However, if you're looking into what file type you can use to import bank transactions manually, here they are:
For more details on the first three files, see upload more than 90 days of bank transactions through Web Connect. If you're going to use .CSV file, see import bank transactions from Excel CSV file to QuickBooks Online.
Leave a comment below if you need additional help.