Elliot and Mr. Robot receive a menu with mysterious numbers they must decode.

Charlie explains, at a high level, how prime numbers are used in modern encryption. He mentions that solving the Riemann Hypothesis could help decrypt current present day encryption, unlocking passwords and bank account information.

Patricia, a cryptanalyst, introduces Alan Turing to the Engima machine and explains how it works. Alan is tasked with breaking the Enigma machine so that the Allies could read the intercepted German messages during World War II.

Since Hacker has a secret device that can listen in on their conversations, Matt, Inez, Jackie, and Digit need to create a way to communicate with each other without Hacker knowing what they are saying. They decide to create a code and an accompanying ruleset so that both the sender and receiver can understand the message. Inez suggests using the page number, line number, and word number within the line of Digit's book, The Cyberchef, to communicate.

The team tests the black box and discovers that it can decrypt data from any encrypted governmental system. One of the members of the group explains that encryption is reliant on complex mathematical computations, and the black box can somehow solve them without an encryption key.