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Application Note

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NG-ULTRA

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bitstream loading security

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Ver 1.0.0

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Table of Content

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Release Notes

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Document History

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Related documentation

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Acronyms

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Summary

This application note, the reference designs and the associated scripts are intended to show NG-ULTRA FPGA bitstream loading security

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Introduction

The NG-ULTRA component is composed of a large embedded FPGA and a digital processor subsystem based on ARM Cortex R52 cores. The bitstream manager (BSM) manages the FPGA fabric configuration.

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Fig 1 – NG-ULTRA bloc diagram

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NG-ULTRA FPGA bitstream security is managed through the implementation of encryption mechanisms applied to the data to be protected. Security function that encodes a digital data using a secret encryption key, making the encoded data unintelligible unless it is decoded using a decryption key.

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Test environment

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Tools

Hardware:

NG-ULTRA Bring-up board

Software:

• NxmapImpulse

• Nxbase2

• Security loader test package tools reference designs, scripts and binary files

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Install plugins NXBASE2 full options

Please install the plugins full options to enable the loading of BTS file with NxBase2.

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• nxbase2_cli/plugins

• nxbase2_cli/nxbase2/plugins

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Bring-up board set up

Bypass mode

Mode useful to test and debug, to bypass all security process.

Tab 1 – Bypass mode selection

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JTAG interface is chained from the SOC to the FPGA and allow to debug the SoC code or to load a bitstream in the FPGA. On the bring-up board, the NG-ULTRA JTAG can be connected by the FPGA SPARTAN6 with the Nxbase2 commands or by the debug mictor interface with the lauterbach Lauterbach trace 32/debug probe or openOCD.

Tab 2 – JTAG master selection

Note:

• This mode can be control controlled through Nxbase2 software (overwrite jumper setup)

• JTAG clock must be < configuration clock / 2

NG-ULTRA configuration mode

Tab 3 – Configuration mode selection

NoteNotes:

• 0 = jumper unset, 1 = jumper set

• This mode can be control through Nxbase2 software (overwrite jumper setup)

FLASH SPI configuration

Tab 4 – FLASH SPI configuration selection

NoteNotes:

• Internal flash selected, Flash_Num selects Flash 0, 1, 2 and 3 on board

• External flash selected, Flash_Num selects Flash 0, 1, 2 on board and Flash 3 external

• This mode can be control through Nxbase2 software (overwrite jumper setup)

Configuration clock

Tab 5 – Configuration clock selection

Note: When programming the Security OTP, the user should set the J20 to have the frequency BSM clock required to write into the OTP memory. (40MHz < clk BSM < 80 MHz)

SOC clock

Tab 6 – SOC clock selection

User clock

Tab 7 – User clock selection

Bring-up board LED

Tab 8 – Bring-up board LED

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Note: At power ON, all voltage LEDs have to be lighted.

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Bring-up board user GPIOs

Tab 9 – Bring-up board user GPIOs

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Note: User GPIOs are activated low

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Bitstream download process

To configure the fabric, the BSM uses rows of drivers. Each driver row manages a subset of logical rows. Each driver row is managed by a Loader module. This Loader module includes all FSM to access to configuration memory.

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A bitstream is a collection of Frames. Each frame as a header and a body. Frame header is a 32b word protected by EDAC. A bitstream includes 2 CRC, Frame CRC that checks the integrity of each fabric configuration frame and Bitstream CRC that checks the integrity of the whole bitstream.

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Fig 2 – BSM bloc diagram

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Test_001 is an example of loading a non-encrypted bitstream with security mode enabled and disabled.

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Loader OTP memory

The loader OTP stores security related data such as keys, seeds for key generation, identifier, anti-rollback counter, secure mode configuration.

Tab 10 – Loader OTP memory contains

NoteNotes:

• Before accessing the OTP memory, it will be bisted and the OTP supplementary address 0x3 and 0x4 must be written with value 0x5555 and 0xAAAA respectively

• When programming the Security OTP, the user should be careful to have the main configuration clock, CLK_BSM between 40 and 80 MHz

• The user should be careful to program the OTP ECC-protected fields only once. If an ECC6 protected field is programmed multiple times, there’s a great chance that the ECC signature becomes unreadable and ends up ‘bricking’ the chip by generating a DED error upon booting

• Some data are masked with the key masking seed before writing into the OTP memory

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Test_004 dump the OTP memory.

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Lifecycles

The lifecycle value is stored in the OTP memory. It determines the bitstream configuration interface and the type of BSM accesses authorized and the type of bitstream (crypted encrypted or non-encrypted).

Fig 3 – Lifecycle diagram

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Lifecycle interfaces and accesses

Tab 3 – Lifecycle interfaces

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Note: The direct access is proceeded by direct engine with BTS file and the frame access is proceeded by frame engine with BBS or NXB file.

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Anti-Rollback

A cyphered ciphered bitstream contains the rollback counter. Deciphering engine compares it to the anti-rollback counter stored into the OTP memory. The check algorithm depends of the life-cycle.

Tab 12 – Lifecycle anti-rollback check

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Test_005 program the security data, lifecycle data, encryption keys and anti-rollback counter.

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Bitstream encryption

Depending on the lifecycle, the encryption must be used to properly load a bitstream.

Bitstream encryption stepsteps:

• Nxmap Impulse has to generate a bitstream in BBS format file

• Remove the comments into the .BBS file to simplify the following padding step

• Some informations information should be added at the beginning of the .BBS file

  • Rollback counter (128b)

  • TAG (128'h2e90_0db0_07ab_7eac_ce55_c0de_de7e_c7ed)

  • Size of the bitstream + padding words expressed in number of 32b word (128b)

  • Bitstream payload

  • Padding words

• Run the encryption script Utils/Encryption/bitstream/encrypth.sh

Note:

• Cyphered Ciphered bitstream is constituted of 128b frames whereas uncyphered enciphered bitstream contains 32b frames. To match size, uncyphered enciphered bitstream must be padded to 128b with dummy data inserted after the uncyphered enciphered bitstream

• There are 0, 1, 2, or 3 padding word maximum

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Test_006 is an example of loading a crypted encrypted bitstream.