I am trying to encrypt a volume with LUKS2 AES-GCM-Random cipher and I am seeing an error saying “key size 256 bits” not available. I tried changing the key size but same error repeats for whatever the key size we give. 

Could you please help us solve this problem.

# cryptsetup --verbose luksFormat --type luks2 --cipher aes-gcm-random --integrity aead /dev/sdb2 

WARNING!

========

This will overwrite data on /dev/sdb2 irrevocably.

Are you sure? (Type 'yes' in capital letters): YES

Enter passphrase for /dev/sdb2: 

Verify passphrase: 

Cipher aes-gcm-random (key size 256 bits) is not available.

Vinay