Building Searchable Encrypted Databases with PHP and SQL
This question shows up from time to time in open source encryption libraries' bug trackers. This was one of the "weird problems" covered in my talk at B-Sides Orlando (titled Building Defensible Solutions to Weird Problems), and we've previously dedicated a small section to it in one of our white papers.

The question is, How do we securely encrypt database fields but still use these fields in search queries?