These references collect background material, cipher tools, and community research that are useful when studying the Kryptos sculpture and the unsolved K4 passage.
Basic info and history about Kryptos
In-depth analysis and breakdown of the Kryptos sculpture
An online tool for decoding and encoding messages
Great breakdowns for different types of ciphers, including auto-solvers and cipher identifier
Online tool for decoding and encoding messages
A blog with tons of great information, going back many many years.