An overview of cryptanalysis research for the advanced encryption standard

Abstract

-Since its release in November 2001, the Advanced Encryption Standard (NIST FIPS-197) has been the subject of extensive cryptanalysis research. The importance of this research has intensified since AES was named, in 2003, by NSA as a Type-1 Suite B Encryption Algorithm (CNSSP-15). As such, AES is now authorized to protect classified and unclassified national security systems and information. This paper provides an overview of current cryptanalysis research on the AES cryptographic algorithm. Discussion is provided on the impact by each technique to the strength of the algorithm in national security applications. The paper is concluded with an attempt at a forecast of the usable life of AES in these applications. Keywords-Advanced Encryption Standard; AES; Cryptanalysis; Side Channel Attacks INTRODUCTIONIn 2003, the National Security Agency took the unprecedented step of approving a public-domain encryption algorithm, AES, for classified information processing. Prior to this milestone, all encryption algorithms approved by the NSA for classified processing were, themselves, classified. The strength of any good encryption algorithm is not enhanced by holding the design as secret. In fact, a public domain encryption standard is subject to continuous, vigilant, expert cryptanalysis. Any breakthroughs will very likely be available to users as well as their adversaries at the same time.In consumer applications, this isn't as much of a problem, but in military communication applications it can be disastrous. Here, the adversary can have national intelligence agency level resources and can exploit vulnerabilities as soon as they are identified. If practical vulnerabilities are found, there will be a period of reduced confidence until a new algorithm can be installed.It is prudent for users and providers of military communications equipment to stay abreast of the progress and trends on cryptanalysis of AES. Facilitating this process is the objective of this paper.Section 2 presents a summary of the past and current areas of research on cryptanalysis of the AES. This section is divided into 5 subsections. The first discusses attacks that pre-existed AES and were addressed as part of its design. The second discusses progress in the new area of algebraic attacks. The third discusses progress on SAT solver and hybrid attacks. Subsection 4 discusses the progress made in side-channel cryptanalysis. Subsection 5 presents a summary of related-key vulnerabilities and distinguishing attacks on AES. These are particularly relevant when AES is used in applications other than traffic encryption (such as hash functions). Section 3 provides discussion of the current strength of AES in national security applications. A forecast of the usable life of AES in these applications is attempted. The paper is concluded in Section 4. CURRENT AREAS OF RESEARCH 2.1Pre-Existing Attacks 2.1.1 Linear Cryptanalysis Linear cryptanalysis exploits approximate linear relationships that exist between inputs and outputs of a function block [1]. In ...

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