Hash functions are used for numerous applications in computer networking, both on classical CPU-based systems and on dedicated hardware like FPGAs. During system development, hardware implementations require particular attention to take full advantage of performance gains through parallelization when using hashes. For many use cases, such as hash tables or Bloom filters, several independent short hash values for the same input key are needed. Here we consider the question how to save resources by splitting one large hash value into multiple sub-hashes. We demonstrate that even small flaws in the avalanche effect of a hash function induce significant deviation from a uniform distribution in such sub-hashes, which allows potential denial-of-service attacks. We further consider the cryptographic hash SHA3 and other non-cryptographic hashes, which do not exhibit such weaknesses, in terms of resource usage and latency in an FPGA implementation. The results show that while SHA3 was intended for security applications, it also outperforms the non-cryptographic hashes for other use cases on FPGAs.
