Developer Comments:

”This algorithm was presented at the ForenSecure 2017 conference on cybersecurity and forensics. The experts attending were not particularly happy after the talk, for their job of trying to detect hidden data had suddenly become quite a bit harder. One year later, I realized the general public might want to check out what it can do, hence this addon.”

PassLok stego is based on the F5 algorithm by Andreas Westfeld (2001), which is described at https://www2.htw-dresden.de/~westfeld/publikationen/21370289.pdf, which is extended to PNG images as well. In addition, PassLok does some simple tricks to preserve the DCT AC coefficient histogram almost perfectly, making it even harder to detect than F5.