Editing Advanced Encryption Standard (section)

=== Optimization of the cipher ===
On systems with 32-bit or larger words, it is possible to speed up execution of this cipher by combining the {{mono | SubBytes}} and {{mono | ShiftRows}} steps with the {{mono | MixColumns}} step by transforming them into a sequence of table lookups. This requires four 256-entry 32-bit tables (together occupying 4096 bytes).  A round can then be performed with 16 table lookup operations and 12 32-bit exclusive-or operations, followed by four 32-bit exclusive-or operations in the {{mono | AddRoundKey}} step.<ref>{{cite book |chapter-url=https://doi.org/10.1007%2F3-540-36400-5_13 |doi=10.1007/3-540-36400-5_13 |chapter=Efficient Software Implementation of AES on 32-Bit Platforms |title=Cryptographic Hardware and Embedded Systems - CHES 2002 |series=Lecture Notes in Computer Science |year=2003 |last1=Bertoni |first1=Guido |last2=Breveglieri |first2=Luca |last3=Fragneto |first3=Pasqualina |last4=MacChetti |first4=Marco |last5=Marchesin |first5=Stefano |volume=2523 |pages=159–171 |isbn=978-3-540-00409-7}}</ref>  Alternatively, the table lookup operation can be performed with a single 256-entry 32-bit table (occupying 1024 bytes) followed by circular rotation operations.

Using a byte-oriented approach, it is possible to combine the {{mono | SubBytes}}, {{mono | ShiftRows}}, and {{mono | MixColumns}} steps into a single round operation.<ref>{{cite web |url=https://code.google.com/p/byte-oriented-aes |title=byte-oriented-aes – A public domain byte-oriented implementation of AES in C – Google Project Hosting |access-date=2012-12-23 |url-status=live |archive-url=https://web.archive.org/web/20130720155538/http://code.google.com/p/byte-oriented-aes/ |archive-date=2013-07-20}}</ref>