Unknown argument --help
Usage: /usr/bin/dropbearkey -t <type> -f <filename> [-s bits]
-t type	Type of key to generate. One of:
		rsa
		ecdsa
		ed25519
-f filename    Use filename for the secret key.
               ~/.ssh/id_dropbear is recommended for client keys.
-s bits	Key size in bits, should be a multiple of 8 (optional)
           ECDSA has sizes 256 384 521
           Ed25519 has a fixed size of 256 bits
-y		Just print the publickey and fingerprint for the
		private key in <filename>.
-C		Specify the key comment (email).