On-chip lookup tables for fast symmetric-key encryption

On public communication networks such as the Internet, data confidentiality can be provided by symmetric key ciphers. One of the most common operations used in symmetric key ciphers are table lookups. These frequently constitute the largest fraction of the execution time when the ciphers are implemented using a typical RISC-like instruction set. To accelerate these table lookups, we describe a new hardware module, called PTLU (for parallel table lookup), which consists of multiple lookup tables that can be accessed in parallel. A novel combinational circuit included in the module can optionally perform simple logic operations on the data read from the tables. On a single issue 64-bit RISC processor, PTLU provides maximum speedups of 7.7x for AES and 5.4x for DES. With wordsize scaling, PTLU speedups are significantly higher than that available through more conventional architectural techniques such as superscalar or VUW execution.