What is a critical action taken after zeroising during the Keymat loading process?

Zeroising refers to the process of clearing sensitive information from cryptographic devices to prevent unauthorized access. A critical action taken immediately after zeroising is to set the Default Fill Port Mode. This step is essential because it prepares the cryptographic device for subsequent operations involving key material.

Setting the Default Fill Port Mode ensures that the system is correctly configured to accept new Keymat (key material) through its designated input ports. This mode establishes the communication protocols and parameters that the device will use to load encryption keys securely and effectively. Without properly configuring the fill port mode, there could be potential issues with key loading, which might compromise the integrity and security of the cryptographic operations.

In contrast, actions such as loading config files, testing crypto keys, or applying power to the network, while important in the broader context of cryptographic operations, occur at different phases in the process and are not the immediate next step following zeroising.