Intel® Arria® 10 Hard Processor System Technical Reference Manual

ID 683711
Date 1/10/2023
Public

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Document Table of Contents

7.1.3.7.3. Authentication and Decryption

Authentication is provided for the second-stage boot loader code and both the HPS and FPGA can utilize the AES algorithms in the Configuration Subsystem (CSS) to decrypt boot images and POF files, respectively.

Three levels of boot are available to the device:

  • Authentication only: The second-stage boot loader code is not encrypted, but there are public key signatures attached to the image and the code only executes if all of the signatures pass. ECDSA256 (SHA 256) is used for authenticated boot.
  • Decryption only: The user boot code is encrypted and must be decrypted before execution. AES-based algorithms in the FPGA are used for decryption.
  • Authentication and Decryption: The user boot code is encrypted and signed.

If authentication and decryption are enabled, the data is first authenticated and then decrypted using the AES algorithms. Authentication is performed using the public key authorization key (KAK) held in the user fuses. The KAK can be 256 bits. The KAK public key authentication fuses are lockable by the user in groups of 64 bits or less.

The Security Manager's hps_fusesec register can be read to identify the source of the public (root) key used for authentication of the second-stage boot loader. The source of the public (root) key can be one of the following:

  • External software
  • ROM
  • FPGA logic elements
  • User Access Fuses (UAF)

AES decryption algorithms are available through the FPGA CSS and are enabled prior to decryption through a combination of user fuses and software programming. Elliptic curve cryptographic algorithms are used in an authenticated boot. Decrypted data is sent to the Security Manager to be read by the CPU or DMA.

The FPGA has higher priority in the CSS, and the FPGA AES algorithms abort decryption and authentication of data if the FPGA starts configuration or reconfiguration.