MicroBitstreams: Reducing Configuration Time of Encrypted Bitstreams

Field Programmable Gate Arrays (FPGAs) are powerful re-programmable hardware devices. The functionality of a FPGA is determined through the configuration file, or bitstream, programmed in at boot-up. However, the boot-up configuration time requires tens to hundreds of milliseconds too long for some boot time-sensitive systems. This problem is exacerbated if bitstream encryption and authentication are used. State-of-the-art techniques to reduce the configuration times of bitstreams consists of configuration frame removal, compressing the bitstream, or partial reconfiguration of the fabric during run time. Often these solutions do not apply encryption or authentication to the final bitstream leaving the user design susceptible to tamper, cloning, and malicious insertions. Our work approaches this problem by splitting the design into two separate bitstreams, a fast “mission critical” bitstream, or MicroBitstream, and a “full feature” bitstream, or secondary bitstream. On boot, only the MicroBitstream is loaded into the FPGA. Even with authentication and encryption, the MicroBitstream is able to load into the FPGA in an average of 1.13 seconds. In addition to the “mission mission critical” features, the MicroBitstream contains a bootloader that will leverage partial reconfiguration to dynamically reprogram the FPGA at run-time to incorporate the full feature set. This technique, named MicroBitstreams, can also be used to enable a wide variety of encryption and authentication schemes on the secondary bitstream. MicroBitstreams applies encryption and authentication to secure the MicroBitstream from tamper, cloning, and malicious insertions. The average decrease in total configuration time when using a MicroBitstream compared to a normal encrypted bitstream is 88.70%, and 57.61% when compared to a encrypted compressed bitstream. MicroBitstreams enables the use of FPGAs in boot time-sensitive systems, thus decreasing program development costs and time spent in the design process.