An Exploration of Embedded Memories Start-Up Patterns as Physical Unclonable Functions

Memory-based Physical Unclonable Functions (PUFs) are normally used for authentication and key generation for hardware security. Various types of memories, such as SRAM, DRAM, and flash, are explored for their effectiveness as PUFs. SRAM (Static Random-Access Memory) has been a prominent choice for PUF applications due to its reliable start-up pattern, which exhibits variability across different chips due to inherent manufacturing differences. DRAM (Dynamic Random-Access Memory) PUF can be based on start-up pattern, DRAM related latency parameters, or DRAM retention. In this paper, we explored both embedded SRAM and SDRAM of an FPGA to be utilized as PUFs. SRAM is, as expected, shown to be effective and reliable as a PUF. Its start-up pattern is well-established for generating unique identifiers. Although SDRAM shows promising randomness, its bit error rate (BER) is high (exceeding 50%), which significantly impacts its reliability as a PUF. A high BER means that the data obtained from the SDRAM can be unreliable, which is critical for PUF applications where consistency is key. Since most of the system has both SRAM and SDRAM, we recommend that SRAM can be utilized continuously for its established reliability as a PUF. Meanwhile, SDRAM with its strong randomness attributes make it a good candidate for a different role, which is a seed for data obfuscation to scramble or obscure data, especially in scenarios where authentication fails, thus enhancing overall security.