Information hiding techniques have recently become important in a number of application areas. Digital audio, video, and pictures are increasingly furnished with distinguishing but imperceptible marks, which may contain a hidden copyright notice or serial number or even help to prevent unauthorised copying directly. Military communications systems make increasing use of traffic security techniques which, rather than merely concealing the content of a message using encryption, seek to conceal its sender, its receiver or its very existence. Similar techniques are used in some mobile phone systems and schemes proposed for digital elections. Criminals try to use whatever traffic security properties are provided intentionally or otherwise in the available communications systems, and police forces try to restrict their use. However, many of the techniques proposed in this young and rapidly evolving field can trace their history back to antiquity; and many of them are surprisingly easy to circumvent. In this article, we try to give an overview of the field; of what we know, what works, what does not, and what are the interesting topics for research.

We initiate the cryptographic study of order-preserving symmetric encryption (OPE), a primitive suggested in the database community by Agrawal et al. (SIGMOD ’04) for allowing efficient range queries on encrypted data. Interestingly, we first show that a straightforward relaxation of standard security notions for encryption such as indistinguishability against chosen-plaintext attack (IND-CPA) is unachievable by a practical OPE scheme. Instead, we propose a security notion in the spirit of pseudorandom functions (PRFs) and related primitives asking that an OPE scheme look “as-random-as-possible ” subject to the order-preserving constraint. We then design an efficient OPE scheme and prove its security under our notion based on pseudorandomness of an underlying blockcipher. Our construction is based on a natural relation we uncover between a random order-preserving function and the hypergeometric probability distribution. In particular, it makes black-box use of an efficient sampling algorithm for the latter. 1

In this tutorial, selected topics of cryptology and of computational complexity theory are presented. We give a brief overview of the history and the foundations of classical cryptography, and then move on to modern public-key cryptography. Particular attention is paid to cryptographic protocols and the problem of constructing key components of protocols such as one-way functions. A function is one-way if it is easy to compute, but hard to invert. We discuss the notion of one-way functions both in a cryptographic and in a complexity-theoretic setting. We also consider interactive proof systems and present some interesting zero-knowledge protocols. In a zero-knowledge protocol, one party can convince the other party of knowing some secret information without disclosing any bit of this information. Motivated by these protocols, we survey some complexity-theoretic results on interactive proof systems and related complexity classes.

Steganography is the art of covered, or hidden, writing. The purpose of steganography is covert communication-- to hide the existence of a message from a third party. This paper is intended as a high-level technical introduction to steganography for those unfamiliar with the field. It is directed at computer forensics examiners who need a practical understanding of steganography without delving into the mathematics, although references are provided to some of the ongoing research for the individual who needs or wants additional detail. While this paper provides a historical context for stego, the emphasis is on digital applications, focusing on hiding information in on-line image or audio files. Examples of software tools that employ steganography to hide data inside of other

We introduce a method for solving substitution ciphers using low-order letter n-gram models. This method enforces global constraints using integer programming, and it guarantees that no decipherment key is overlooked. We carry out extensive empirical experiments showing how decipherment accuracy varies as a function of cipher length and n-gram order. We also make an empirical investigation of Shannon’s (1949) theory of uncertainty in decipherment. 1

Abstract. Superconvergence phenomenon of the Legendre spectral collocation method and the p-version finite element method is discussed under the one dimensional setting. For a class of functions that satisfy a regularity condition (M): ‖u (k) ‖L ∞ ≤ cM k on a bounded domain, it is demonstrated, both theoretically and numerically, that the optimal convergent rate is supergeometric. Furthermore, at proper Gaussian points or Lobatto points, the rate of convergence may gain one or two orders of the polynomial degree. 1.

Abstract: Frequency analysis is the fundamental cryptanalytic technique besides brutal force, threat, blackmail, torture, bribery, etc. [1]. Conventionally, it is applied on monogram, bigram and trigram together with anagramming technique [2]. The efficiency of anagramming depends on the cryptanalyst's depth of knowledge in different language features. Hence anagramming is a trial-and-error approach due to huge deviation in different fields, e.g. military, diplomatic, commercial, legal and daily languages. The frequency fluctuations among the normal frequency order of the characters trigger the crossover problem for monogram frequency analysis. Meanwhile bigram and trigram frequency analyses are found to give little help. Higher orders are unlikely to be useful. In 1994, George Hart introduced a novel frequency analysis approach based on word frequency to decode the enhanced frequency analysis for systematic decryption of English ciphertext [3]. The proposed protocol uses combined techniques of monogram frequency analysis, keyword rules and dictionary checking. It is successfully tested faster on monoalphabetic substitution cipher. Moreover, it solves the weakness of Hart’s approach for complete failure when neither top 135 words is found in the ciphertext. Further extrapolation is expected to be applicable to other cryptanalytic algorithms and languages.

In this work, we tackle the task of machine translation (MT) without parallel training data. We frame the MT problem as a decipherment task, treating the foreign text as a cipher for English and present novel methods for training translation models from nonparallel text. 1

The prisoners' problem is a typical model of steganography, in whicht wo persons attempt to communicate covertly without alerting the warden. That is, only the receiver knows the existence of message sent by the sender. One available way to achieve this task is to embed the message in an innocuous-looking cover-media. On the other hand, for avoiding the covert communication taking place, the warden may be allowed to slightly modify messages as they are sent between prisoners. In this paper, we will propose an image steganographic model in which the hidden message can survive the image modification. Experimental results show these created stegoimages are innocuous looking and the hidden message is robust enough to resist against some image processing operations.

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