02-05-2014 12:47 AM
Hi, I'm having some questions on encrypted bitstreams in virtex-5.
1) In Virtex-5 FPGA Configuration Guide UG191 it states that Fallback reconfiguration is disabled after encryption is enabled. Why is this the case?
2) In "Solving Today's Design Security Concerns WP365" it says: Authentication such as in Virtex-6 protects from altering the bitstream. What does this mean? Can an attacker modify a bit in an encrypted bitstream and the device would still configure if authentication isn't used?
02-05-2014 08:58 AM
1. In order to prevent attacks, any features that attempt to recover are not enabled (as that would aid an attacker).
2. The methods used prevent changing any bit (any change forces the bitstream to be rejected). This is also important in security (cryptography). Read about authentication The authetication is built in, it cannot be disabled as it is part of the decryption process. V5 does allow some types of attack, as its authentication was not as robust as later devices.
02-05-2014 10:20 AM
The below link documents give some useful information for your requirement
02-06-2014 01:25 PM
Thanks for your answers,
1) Would you care to explain why fallback with encrypted bitstreams could aid an attacker? Are two bitstreams encrypted with the same key be less secure than one?
2) OK, I understand now the authentication (in V6) is part of the config process and isn't optional.
Although possible to manipulate, the encrypted V5 bitstreams would not be possbile to copy. Is that correct?
Your last link leads to this thread. Was that inentional?
02-06-2014 01:47 PM
1. I leave that up to you to figure out. It isn't up to me to help attackers succeed in an attack. If you do not recognize it as a weakness, I am not going to explain it to you.
2. A copy of the encrypted bitstream is easy to make. And, if you know the key, easy to use. Tying a bitstream to a specific device requires a unique bitstream/key pair. Or, it must somehow use something unique about that specific FPGA device. To enable that capability is presently something that has lot of people seriously trying to figure out a reliable method to do.
02-06-2014 02:14 PM
1) I think you'll be perfectly safe telling me how. I, or anyone else for that matter, could not use this attack method since V5 does not support fallback with encrypted bitfiles anyhow!
2) OK thanks for clarifying.