Researchers Break FPGA Encryption Using FPGA Encryption

FPGAs are awesome — they can be essentially configured into becoming any computing device you want. Simply load your selected bitstream into the device on boot, and it behaves like a different piece of hardware. With great power comes great responsibility.

You might try to hack a given FPGA system by getting between the EEPROM that stores the bitstream and the FPGA during bootup, but FPGA manufacturers are a step ahead of you. Xilinx 7 series FPGAs have an onboard encryption and signing engine, and facilities for storing a secret key. Once the security bit is set, bitstreams coming in have to be encrypted to protect from eavesdropping, and HMAC-signed to assure that they are authentic. You can’t simply read the bitstream in transit or inject your own.

Researchers at Ruhr University Bochum and Max Planck Institute for Cybersecurity and Privacy in Germany have figured out a way to use the FPGA’s own encryption engine against itself to break both of these security guarantees for the entire mainstream 7-series. The attack abuses a MultiBoot function that allows you to specify an address to begin execution after reboot. The researchers send 32 bits of the encoded payload as a MultiBoot address, the FPGA decrypts it and stores it in a register, and then resets because their command wasn’t correctly HMAC signed. But because the WBSTAR register is meant to be readable on boot after reset, the payload is still there in its decrypted form. Repeat for every 32 bits in the bitstream, and you’re done.

Pulling off this attack requires physical access to the FPGA’s debug pins and up to 12 hours, so you only have to worry about particularly dedicated adversaries, but the results are catastrophic — if you can reconfigure an FPGA, you can make it do essentially anything. Security-sensitive folks, we have three words of consolation for you: “restrict physical access”.

What does this mean for Hackaday? If you’re looking at a piece of hardware with a hardened Xilinx 7-series FPGA in it, you’ll be able to use it, although it’s horribly awkward for debugging due to the multi-hour encryption procedure. Anyone know of a good side-channel bootloader for these chips? On the other hand, if you’re just looking to dig secrets out from the bitstream, this is a one-time cost.

This hack is probably only tangentially relevant to the Symbiflow team’s effort to reverse-engineer an open-source toolchain for this series of FPGAs. They are using unencrypted bitstreams for all of their research, naturally, and are almost done anyway. Still, it widens the range of applicability just a little bit, and we’re all for that.

[Banner image is a Numato Lab Neso, and comes totally unlocked naturally.]

Final Fantasy Exploit Teaches 32-bit Integer Math

One of the fun things about old video games, besides their obvious nostalgia, is that some of the more popular games have been pried apart and tinkered with for years, leading to a lot of new “development” within the games. This often uncovers some hidden gems that gamers might not have had any knowledge of during the game’s heyday, like this coding oddity found in Final Fantasy 7 that illustrates a lot about how 32-bit processors do math.

The original PlayStation used a 32-bit RISC processor, but the most significant bit could be used for integer signing. This means that if you have an integer that has a value of 2,147,483,647 (01111111111111111111111111111111 in binary) and you add one, the value is suddenly negative 2147483648 because the most significant digit is also an indicator of the integer’s sign. In this situation, the integer is said to “overflow”. In Final Fantasy 7, if you can somehow get a character to deal 262,144 damage in one hit (much less than two billion, due to the way the game does damage calculations), the game has a little bit of a meltdown.

[4-8Productions] had to do a lot of work to show how this glitch can be exploited in the game as well. Usually damage in this game is limited to 9,999 but under certain configurations (admittedly obtained by using other exploits and tools available for FF7 like a savegame editor) two of the characters can deal more damage than this critical value, exposing the 32-bit processor’s weak spot.

Even though integer signing is a pretty basic concept for most of us, the video is definitely worth a watch especially if you’re fans of the classic game. Of course, Final Fantasy 7 isn’t the only classic that has been exploited and reverse-engineered to the extreme. You can use a Super Mario World level to implement a calculator now, too.

Continue reading “Final Fantasy Exploit Teaches 32-bit Integer Math”

Red Hat Confirms Security Breach

After a week of wondering, Red Hat has confirmed that someone broke in and compromised their security. Although It doesn’t appear the attacker was able to retrieve the passphrase used to sign Fedora packages, the team is switching to new keys. In a separate intrusion the attacker tampered with and signed OpenSSH packages for RHEL. While it’s good to get the full story, no one is happy how long it took Red Hat to release these details.

[via Zero Day]

[photo: afsilva]