Tux image (and derivates) by Larry Erwing made with The GIMP under following conditions: "Permission to use and/or modify this image is granted provided you acknowledge me lewing@isc.tamu.edu and The GIMP if someone asks."
Those can be found on Wikipedia/Block cipher mode of operation and are made by different authors in public domain.
Block cipher mode of operation: Wikipedia/Block cipher mode of operation
"TEA, a Tiny Encryption Algorithm": Original Paper