These are called "cache-timing attacks". In presence of caches, no memory lookup can be guaranteed to be constant time. Any memory lookups that use secret indic

These are called "cache-timing attacks". In presence of caches, no memory lookup can be guaranteed to be constant time. Any memory lookups that use secret indices are thus not timing-safe, however non-secret indices are OK. See https://cr.yp.to/antiforgery/cachetiming-20050414.pdf https://cr.yp.to/antiforgery/cachetiming-20050414.pdf Here's an implementation that doesn't use tables: https://github.com/openbsd/src/blob/master/sys/crypto/aes.c https://github.com/openbsd/src/blob/master/sys/crypto/aes.c