It's my understanding that LUKS encrypts data by using a randomly-generated master-key, which is then itself stored encrypted by my passphrase. When I want to access the data, I use my passphrase to decrypt the master-key, which is then used to decrypt the data.
Question: Is it possible to have LUKS just encrypt the data by using the randomly-generated master-key (can I specify the size?), but then instead of encrypting this with my passphrase and storing it, just tell me the master-key (which I will memorize or write on a piece of paper). When I'll want to access the data, I will use the masterkey to decrypt it.
As a side note, let me explain why I think that this would be more secure than the usual procedure: when cryptographically sanitizing a USB or non self-encrypting SSD drive (or changing the LUKS password), it's my understanding that the master-key encrypted by the old password will always be physically present on the drive, because digital sanitization is hard to achieve for USB and SSD. The randomly-generated master-key would then be recoverable by either guessing the old password, or by brute-forcing it.