On the Construction and Cryptanalysis of Multi-Ciphers.

In this compilational work, we combine various techniques from classical cryptography and steganography to construct ciphers that conceal multiple plaintexts in a single ciphertext. We name these “multiciphers”. Most notably, we construct and analyze a Four-In-One-Cipher: the first cipher which conceals four separate plaintexts in a single ciphertext. Following a brief overview of classical cryptography and steganography, we consider strategies that can be used to creatively combine these two fields to construct multi-ciphers. Finally, we analyze three multi-ciphers which were constructed using the techniques described in this paper. This cryptanalysis relies on both traditional algorithms that are used to decode classical ciphers and new algorithms which we use to extract the additional plaintexts concealed by the multi-ciphers. We implement these algorithms in Python, and provide code snippets. The primary goal of this work is to inform others who might be otherwise unfamiliar with the fields of classical cryptography and steganography from a new perspective which lies at the intersection of these two fields. The ideas presented in this paper could prove useful in teaching cryptography, statistics, mathematics, and computer science to future generations in a unique, interdisciplinary fashion. This work might also serve as a source of creative inspiration for other cipher-making, code-breaking enthusiasts. 1 Background and Related Work We briefly summarize relevant background information. Related work on the concept of a “multi-cipher” is referenced in 1.4. Note that in the full version of the paper, which can be accessed here, we include three full-length sections on background related to the field of classical cryptography, the cryptanalysis of classical ciphers, and steganography. These sections are useful to a reader who is unaquainted with the field of cryptography and would make this paper accessible to people outside of academic circles. However, since the audience, in this case, is the research community, we assume that they have familiarity with the basics, and only include summaries. 1.1 Classical Cryptography Most of the encryption algorithms that we use to keep our information secure on the Internet today have been proven secure through higher-level theoretical mathematical models. This is modern cryptography, concerned with proving the security of existing algorithms and designing new algorithms that have applicability in the real world. Classical cryptography, on the other hand, revolves around how ciphers were used in the past. Today, classical cryptography is less concerned with designing new ciphers and more concerned with designing algorithms to implement and break historical ciphers using modern computing methods. Secret codes and ciphers have long been used to encrypt confidential information. But most historical ciphers have fallen into disuse due to their weaknesses in our modern compututing world. Though historical ciphers aren’t used often, they still serve a valuable role. They help us to learn from our mistakes, ensuring that we don’t