July 10, 2008 -- Over the past two decades, the field-programmable gate array (FPGA) has transitioned from a prototyping tool to a flexible production solution in both consumer and industrial applications. With FPGA logic complexity increasing from a few thousand gates to millions of gates, the devices are able to hold more of the key functions (intellectual property) of a system.

Today, designers can select FPGAs that employ various technologies to hold the configuration data—one-time programmable antifuses, reprogrammable flash-based storage cells, and reprogrammable SRAM-based configurable logic cells. Both antifuse- and flash-based solutions provide relatively secure solutions, since the configuration data is stored on the FPGA and there are mechanisms that prevent the stored data from being read out. And, unless very sophisticated schemes such as depacking, microprobing, voltage contrast electron-beam microscopy, and focused ion- beam (FIB) probing are used to pry into the silicon and to disable security mechanisms, it’s very unlikely that the data will be compromised.

Static-RAM-based (SRAM) FPGAs, however, have fewer safeguards to protect that IP (the configuration data) against illegal copying and theft. The reason is that once the data is loaded, it’s held in SRAM memory cells. Such cells can easily be probed to determine their contents. In addition, without some type of security mechanism to protect the configuration data before it’s loaded into the chip, that data is open to snooping. That’s because the bit stream is usually stored in a separate memory chip read by the FPGA upon power-up to load its configuration pattern. There are, though, some simple ways to secure that data to prevent someone from copying the configuration pattern (stealing the IP).

By Bernhard Linke. (Linke is a principal member of the Technical Staff at Maxim Integrated Products, Inc.)