Why is all my data gone if I overwrite the LUKS header?
Overwriting the LUKS header in part or in full is the most common reason why access to LUKS containers is lost permanently. Overwriting can be done in a number of fashions, like creating a new filesystem on the raw LUKS partition, making the raw partition part of a raid array and just writing to the raw partition.
The LUKS header contains a 256 bit "salt" value and without that no decryption is possible. While the salt is not secret, it is key-grade material and cannot be reconstructed. This is a cryptographically strong "cannot". From observations on the cryptsetup mailing-list, people typically go though the usual stages of grief (Denial, Anger, Bargaining, Depression, Acceptance) when this happens to them. Observed times vary between 1 day and 2 weeks to complete the cycle. Seeking help on the mailing-list is fine. Even if we usually cannot help with getting back your data, most people found the feedback comforting.
If your header does not contain an intact salt, best go directly to the last one ("Acceptance") and think about what to do now. There is one exception that I know of: If your LUKS container is still open, then it may be possible to extract the master key from the running system. Ask on the mailing-list on how to do that and make sure nobody switches off the machine.
[...]
What happens if I overwrite the start of a LUKS partition or damage the LUKS header or key-slots?
There are two critical components for decryption: The salt values in the header itself and the key-slots. If the salt values are overwritten or changed, nothing (in the cryptographically strong sense) can be done to access the data, unless there is a backup of the LUKS header. If a key-slot is damaged, the data can still be read with a different key-slot, if there is a remaining undamaged and used key-slot. Note that in order to make a key-slot unrecoverable in a cryptographically strong sense, changing about 4-6 bits in random locations of its 128kiB size is quite enough.
