Cryptography
Cryptography
[Randall Munroe (drawn as Cueball) stands behind a lectern on a podium in front of a large conference audience (consisting of Cueball heads), with a poster hanging beside him.] Randall: My cryptosystem is like any Feistel cipher, except in the S-Boxes we simply take the bitstring down, flip it, and reverse it.
[The poster reads:] Decryption 01101010 >> 00110101 [inverter symbol] 11001010 [crossed arrows] 01010011
[Caption below the crowd:] I've been barred from speaking at any major cryptography conferences ever since it became clear that all my algorithms were just thinly disguised Missy Elliott songs.

This comic refers to the study of cryptography . We can note the presence of the International Association for Cryptologic Research (IACR) logo in the lectern ( podium? ), an association that organizes the most important conferences in the cryptology field.
Randall , drawn as Cueball behind the lectern at the podium, is describing a proposed crypto system in which a computer program turns a very large number, called the " key ," and a message into an encrypted form that can only be read by using the same key, based on the model of a Feistel cipher . Part of any Feistel cipher is the "round function," which determines how the key is applied to the original message; this is applied multiple times with a variety of tricks and techniques to ensure that the process can eventually be reversed. One common component of round functions is the S-box , a simple table that converts input bytes into output bytes, preferably in a way that doesn't correspond to any mathematical rules.
Here, the S-box would be implemented by doing the following (with the computer operation actually shown in the diagrams indicated in parentheses):
This would be run on each round of the cipher to further scramble the message for the next round. As the caption implies, the steps are based on a line from the Missy Elliott song Work It : "I put my thing down, flip it and reverse it." As with any encryption system, there must be a way to decrypt the cipher text. In Missy Elliott's song, the phrase "I put my thing down, flip it and reverse it" is repeatedly played backward, sounding like gibberish. In the same way, steps to a Feistel cipher-based algorithm are executed in reverse to obtain the original plain text from a cipher text.
The keyspace for a cryptographic algorithm is the number of possible keys the algorithm can possibly accept. For example, AES-256 has a keyspace of 2 256 (roughly 1.1579209e+77) possible keys, simply because the algorithm specifies that each key is 256 bits wide. The title text is referring to "searching a keyspace," which is to say, simply trying every key until you find one that works. (For reference, a computer would require roughly the energy of a billion billion supernovas to even count to 2 256 , let alone actually try each one.) The precise wording, "If you got a big keyspace, let me search it" is, of course, another reference to the same song: "If you got a big **** let me search ya" (The word "penis" is censored by the trumpeting of an elephant).
This was the first comic where Randall was banned from conferences. Since then, he has been banned from multiple conferences for similar pranks; especially in 541: TED Talk , there is a whole list of conferences from which he has been banned. This has sometimes resulted in him being invited to those conferences - see more here on this PyCon response to Randall claiming he was banned from their conference.
[Randall Munroe (drawn as Cueball) stands behind a lectern on a podium in front of a large conference audience (consisting of Cueball heads), with a poster hanging beside him.] Randall: My cryptosystem is like any Feistel cipher, except in the S-Boxes we simply take the bitstring down, flip it, and reverse it.
[The poster reads:] Decryption 01101010 >> 00110101 [inverter symbol] 11001010 [crossed arrows] 01010011
[Caption below the crowd:] I've been barred from speaking at any major cryptography conferences ever since it became clear that all my algorithms were just thinly disguised Missy Elliott songs.
