This slot can be used to store a secret 32-byte value or key. This key can
be used with the ECC608-TNGHNT’s symmetric key commands
(GenDig, MAC, CheckMac,
KDF, SHA/HMAC, AES).
Writing this key requires an encrypted write with the IO protection key as the write key. Therefore, the I/O Protection Key must be set before the secret key can be written.