This talk is an introduction to finding and exploiting vulnerabilities in block ciphers using FEAL-4 as a case study. Attendees will learn how cryptanalysis can be used to break ciphers by finding the key with less computational effort than exhaustive search. After an introduction to block cipher components and structure, we will study the incredibly broken FEAL-4 algorithm. By exploiting statistical biases in the cipher, attendees will learn how to build a differential attack and ultimately recover the key. Attendees should have a basic understanding of binary operations like XOR and a general familiarity with bits and bytes. Jon will guide attendees through the fundamentals of modern cryptanalysis while keeping the math to a minimum. That said, this talk is focused on the nitty gritty details of cipher vulnerabilities and how differential cryptanalysis can be applied to them.