Secret sharing scheme distribute the secret key among multiple participants to ensure the reliability of the key. A new version of secret sharing called counting-based secret sharing (CBSS) has emerged to divide the secret key into multiple shares (copies of the secret key with some modifications) and distribute these key shares among several individuals in such a way that only the authorized subset of participants needs to agree together to reconstruct the original secret key. Existing CBSS schemes suffer from heavy computational and storage requirements for generating the key shares and reconstructing the secret key, and are also vulnerable to share leakage. This research overcomes the challenges that appear in the existing CBSS methods by dividing the secret key into adjacent blocks and by generating ambiguous secret shares based on block-based masking. In this approach, the secret shares are generated by XOR-ing each separate block of the secret key with a specific sequence of 1s where the total number of 1 is determined based on the block size. Our proposed approach can also reconstruct the secret key efficiently by assembling a subset of shares following a threshold (minimum number of secret shares that are able to reconstruct the secret key). Through experimentation, we found that our proposed CBSS strategy offers a remarkably secure contribution in making a tradeoff between security and cost of computation. Our experiment results also suggest that the average similarity between the secret key and secret shares decreases and the security level increases, when the block size of the secret key in our proposed strategy increases.

Steganography is the art of hiding and transmitting data within innocuous carriers to conceal secret information. Several steganography tools are available on the Internet. Most tools are developed independently, without disclosing their steganographic hiding methods. However, most steganographic hiding methods described in the literature are not directly implemented as tools. Some studies categorize hiding methods without properly associating them with the related tools. As a result, there is a technical gap between the steganographic hiding methods described in the literature and the steganography tools available on the Internet. To close this gap, we classify steganography tools based on their hiding methods. In addition, we consider the multimedia formats of cover media, which are closely related to hiding methods and are not adequately described in the literature. Besides the existing method of categorizing hiding methods, we propose three different ways to do so. We also propose a complexity matrix to further classify the tools. Finally, we suggest a strategy to identify the possibility of finding a signature present in a tool and validate it using a benchmark dataset. The same strategy can be applied to classify the tools based on some hiding methods.

In this article, I investigate the hypothesis that the Voynich Manuscript (MS 408, Yale University Beinecke Library) is compatible with being a ciphertext by attempting to develop a historically plausible cipher that can replicate the manuscript’s unusual properties. The resulting cipher—a verbose homophonic substitution cipher I call the Naibbe cipher—can be done entirely by hand with 15th-century materials, and when it encrypts a wide range of Latin and Italian plaintexts, the resulting ciphertexts remain fully decipherable and also reliably reproduce many key statistical properties of the Voynich Manuscript at once. My results suggest that the so-called “ciphertext hypothesis” for the Voynich Manuscript remains viable, while also placing constraints on plausible substitution cipher structures.

Schlüsselgerät 41 (cipher device 41) is a rare but very advanced mechanical cipher machine from World War II. It was developed by Fritz Menzer in 1941, and used by the German Abwehr at the end of the war. Virtually nothing was known about this machine until the last decade. The authors of this study recently succeeded in finding the previously missing operating instructions and key documents in Czech archives. As a result, last unanswered questions about how the machine worked and how it was used in the field can now be clarified.

This article describes the work done by codebreakers in the Naval Section at Bletchley Park on the primary World War II Japanese naval cipher JN-25. It also describes the relationship between the US Navy’s OP-20-G and Bletchley Park’s JN-25 codebreakers. To put the work at Bletchley Park into context, the initial breaks into JN-25, the changes to JN-25, the formal agreements between OP-20-G and the Government Code and Cypher School, and various techniques that used differencing of additive-enciphered code are described in detail. In many cases, the story is told using the words of the World War II codebreakers.

Many of the new quantum-resistant digital signature algorithms being evaluated and standardized by NIST rely on the Fiat-Shamir transform for security. This transformation takes a zero-knowledge (or negligible-knowledge) proof of identity and a hash function, and produces an algorithm for a digital signature. Luckily, none of these concepts are very hard to explain! I will give quick introductions to zero-knowledge proofs and hash functions, followed by two examples of digital signature algorithms based on Fiat-Shamir which you could use in an undergraduate classroom. The first one involves a lot of audience participation, and gives opportunities for drawing and decoration if you are so inclined. The second has been fairly well-known since the early days of public-key cryptography, and is likely to at least remind you of systems you have seen before. We wrap up with an overview of how Fiat-Shamir is used in post-quantum cryptography and in blockchains.

In this paper, we study the imbalance of N-ary half- l -sequences as well as their arithmetic autocorrelation. The arithmetic correlation or “with-carry” correlation is an analog of the classical correlation of sequences. We obtain three families of N-ary half- l -sequences with ideal arithmetic autocorrelation in the case when the connection number of sequences is not a power of a prime. Also, it is shown that in many other cases there are no balanced N-ary half- l -sequences with ideal arithmetic autocorrelation. Our method is based on the properties of sums of Legendre symbols.