4 Security Features

Traditionally, digitally controlled power designs, whether using I²C, SMBus, PMBus, SVID or some other digital interface, have relied on the security of the bus controller devices to prevent malicious actors from gaining access and using the digital control to shut down the converter or even damage hardware. That was considered good enough for most applications. With the ever increasing presence of digital interfaces, and ever more sophisticated threats, that is no longer always sufficient to make sure the integrity of a system. When a device is connected to a remote interface, there is the possibility for remote actors to gain access the digital bus through one of the connected devices, and potentially send malicious commands over the bus. Table 4-1 shows the latest DC/DC converters with security features.

The PASSKEY feature provides the designer with a intermediate level of security between the open security, and the permanent lock created by using the write-protect command for protection. PASSKEY is a 16-bit digital key. When set, PASSKEY disabled write access to both EXT_WRITE_PROTECT and the User NVM store until the PASSKEY is written back to the device. To protect devices from brute force attacks, PASSKEY is limited to three failed PASSKEY write attempts per power-cycle.

Level 2 security uses a 32 byte pre-shared key (PSK) to perform device attestation and authenticated updates. Both of these functions use a combination of SHA2-384 and HMAC SHA2-256 hash algorithms within the device to calculate the message authentication code (MAC). In the case of device attestation, the MAC calculated by the device is compared to an expected MAC to verify the device has the correct PSK programmed and NVM configuration.