> The way to protect secure hardware tokens is not bitstream encryption, it's tamper protection. You store the key material in SRAM that is erased when the device detects any attempt at manipulating.
You need both. First, make all external storage (that hold keys, firmware, configurations) unreadable to everything else besides the main processor itself. Also, in the ideal world, implement tamper detection, in most HSMs there are tamper detections, but unfortunately, the world is not ideal, in the FOSS world, I don't see anything that uses tamper detection, developing an open source tamper detection is something has great value to the community, yet, I don't see it happening at anytime soon. Also, the majority of security token/hardware have no tamper detection - SIM cards, bank cards, OpenPGP cards (Yubikeys, Nitrokeys), smartphones, they only depend on encrypting external storage and/or restrict the access of the secret inside a chip to maintain security. In practice, they still have an above-average security level, it clears shows tamper protection is not the only way to protection the hardware, although it's less effective and occasionally something is going to be broken, to be sure.
This specific FPGA bitstream encryption vulnerability may be a non-issue, as pointed out by the critics, relying on external storage is not a good idea to begin with, better to burn everything inside the FPGA. My point is that FPGAs are the only platform to implement FOSS security hardware in the most (relatively) transparent and secure manner, yet, the recent discoveries of FPGAs vulnerabilities indicates they are much less secure than expected, and it's only the tip of an iceberg. If external bitstream encryption has cryptographic vulnerabilities, what comes next? More broken cryptos that allow you to read an internal key?
You need both. First, make all external storage (that hold keys, firmware, configurations) unreadable to everything else besides the main processor itself. Also, in the ideal world, implement tamper detection, in most HSMs there are tamper detections, but unfortunately, the world is not ideal, in the FOSS world, I don't see anything that uses tamper detection, developing an open source tamper detection is something has great value to the community, yet, I don't see it happening at anytime soon. Also, the majority of security token/hardware have no tamper detection - SIM cards, bank cards, OpenPGP cards (Yubikeys, Nitrokeys), smartphones, they only depend on encrypting external storage and/or restrict the access of the secret inside a chip to maintain security. In practice, they still have an above-average security level, it clears shows tamper protection is not the only way to protection the hardware, although it's less effective and occasionally something is going to be broken, to be sure.
This specific FPGA bitstream encryption vulnerability may be a non-issue, as pointed out by the critics, relying on external storage is not a good idea to begin with, better to burn everything inside the FPGA. My point is that FPGAs are the only platform to implement FOSS security hardware in the most (relatively) transparent and secure manner, yet, the recent discoveries of FPGAs vulnerabilities indicates they are much less secure than expected, and it's only the tip of an iceberg. If external bitstream encryption has cryptographic vulnerabilities, what comes next? More broken cryptos that allow you to read an internal key?