KLS Backup can use Backblaze B2 Cloud Storage to store backup archives or as a backup source.

Application keys (app keys) control access to your Backblaze B2 Cloud Storage account. There are two type of keys you can create: Standard Application Keys and Master Application Keys.

Standard Application Keys

You can create standard app keys that have access to all buckets in an account or just a single bucket. Standard app keys have limited capabilities, can support a specific file prefix, and can expire.

Master Application Keys

The master app key is the first key that you have access to and provides complete access to your account. This key has all capabilities, access to all buckets, and has no file prefix restrictions or expiration. Your master app key is shown only when you generate it, and it is not shown again. You should save your master app key in a secure location if you plan to use it more than once. Your master app key becomes invalid if you generate a new one.

See the official Backblaze documentation: Application Keys.

KLS Backup supports both Standard and Master Application Keys. Use the Backblaze B2 Account dialog to set up the connection.

The App keyID field field should be filled when using a Standard Application Key. For a Master Application Key, this field should be left empty. The Application key field should contain either the Master or the Standard Application Key, depending on whether the App keyID is provided.