SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> III. APPLICATIONS OF SHA-2 <s> The use of cryptographic hash functions like MD5 or SHA-1 for message authentication has become a standard approach in many applications, particularly Internet security protocols. Though very easy to implement, these mechanisms are usually based on ad hoc techniques that lack a sound security analysis. ::: ::: We present new, simple, and practical constructions of message authentication schemes based on a cryptographic hash function. Our schemes, NMAC and HMAC, are proven to be secure as long as the underlying hash function has some reasonable cryptographic strengths. Moreover we show, in a quantitative way, that the schemes retain almost all the security of the underlying hash function. The performance of our schemes is essentially that of the underlying hash function. Moreover they use the hash function (or its compression function) as a black box, so that widely available library code or hardwair can be used to implement them in a simple way, and replaceability of the underlying hash function is easily supported. <s> BIB001 </s> SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> III. APPLICATIONS OF SHA-2 <s> William Stallings' Cryptography and Network Security: Principles and Practice, 5e is a practical survey of cryptography and network security with unmatched support for instructors and students. In this age of universal electronic connectivity, viruses and hackers, electronic eavesdropping, and electronic fraud, security is paramount. This text provides a practical survey of both the principles and practice of cryptography and network security. First, the basic issues to be addressed by a network security capability are explored through a tutorial and survey of cryptography and network security technology. Then, the practice of network security is explored via practical applications that have been implemented and are in use today. An unparalleled support package for instructors and students ensures a successful teaching and learning experience. The new edition has been updated to include coverage of the latest topics including expanded coverage of block cipher modes of operation, including authenticated encryption; revised and expanded coverage of AES; expanded coverage of pseudorandom number generation; new coverage of federated identity, HTTPS, Secure Shell (SSH) and wireless network security; completely rewritten and updated coverage of IPsec; and a new chapter on legal and ethical issues. <s> BIB002 </s> SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> III. APPLICATIONS OF SHA-2 <s> This paper studies the security of SHA-256, SHA-384 and SHA-512 against collision attacks and provides some insight into the security properties of the basic building blocks of the structure. It is concluded that neither Chabaud and Joux’s attack, nor Dobbertin-style attacks apply. Differential and linear attacks also don’t apply on the underlying structure. However we show that slightly simplified versions of the hash functions are surprisingly weak : whenever symmetric constants and initialization values are used throughout the computations, and modular additions are replaced by exclusive or operations, symmetric messages hash to symmetric digests. Therefore the complexity of collision search on these modified hash functions potentially becomes as low as one wishes. <s> BIB003 </s> SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> III. APPLICATIONS OF SHA-2 <s> In this paper, we present new collision search attacks on the hash function SHA-1. We show that collisions of SHA-1 can be found with complexity less than 269 hash operations. This is the first attack on the full 80-step SHA-1 with complexity less than the 280 theoretical bound. <s> BIB004 </s> SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> III. APPLICATIONS OF SHA-2 <s> MD5 is one of the most widely used cryptographic hash functions nowadays. It was designed in 1992 as an improvement of MD4, and its security was widely studied since then by several authors. The best known result so far was a semi free-start collision, in which the initial value of the hash function is replaced by a non-standard value, which is the result of the attack. In this paper we present a new powerful attack on MD5 which allows us to find collisions efficiently. We used this attack to find collisions of MD5 in about 15 minutes up to an hour computation time. The attack is a differential attack, which unlike most differential attacks, does not use the exclusive-or as a measure of difference, but instead uses modular integer subtraction as the measure. We call this kind of differential a modular differential. An application of this attack to MD4 can find a collision in less than a fraction of a second. This attack is also applicable to other hash functions, such as RIPEMD and HAVAL. <s> BIB005 </s> SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> III. APPLICATIONS OF SHA-2 <s> MD5 is a well-known and widely-used cryptographic hash function. It has received renewed attention from researchers subsequent to the recent announcement of collisions found by Wang et al. [16]. To date, however, the method used by researchers in this work has been fairly difficult to grasp. In this paper we conduct a study of all attacks on MD5 starting from Wang. We explain the techniques used by her team, give insights on how to improve these techniques, and use these insights to produce an even faster attack on MD5. Additionally, we provide an MD5 Toolkit implementing these improvements that we hope will serve as an open-source platform for further research. Our hope is that a better understanding of these attacks will lead to a better understanding of our current collection of hash functions, what their strengths and weaknesses are, and where we should direct future efforts in order to produce even stronger primitives. <s> BIB006 </s> SHA-2 Acceleration Meeting the Needs of Emerging Applications: A Comparative Survey <s> III. APPLICATIONS OF SHA-2 <s> Besides attracting a billion dollar economy, Bitcoin revolutionized the field of digital currencies and influenced many adjacent areas. This also induced significant scientific interest. In this survey, we unroll and structure the manyfold results and research directions. We start by introducing the Bitcoin protocol and its building blocks. From there we continue to explore the design space by discussing existing contributions and results. In the process, we deduce the fundamental structures and insights at the core of the Bitcoin protocol and its applications. As we show and discuss, many key ideas are likewise applicable in various other fields, so that their impact reaches far beyond Bitcoin itself. <s> BIB007
The properties of cryptographic hash functions make them one of the most versatile cryptographic tools, used in a variety of security services BIB002 . Digital signature schemes based on asymmetric encryption, such as Digital Signature Algorithm (DSA)  , employ hash functions to reduce their computational complexity while retaining the nonrepudiation property. Due to the processing time of asymmetric cryptography, it would be impractical to directly process a large file to obtain its digital signature, so only the hash of the file is signed. Due to the collision resistance property, it is computationally infeasible to find a second file with the same hash, and hence the same signature, of the original file, thereby preserving the nonrepudiation property. Hash-Based Message Authentication Codes (HMACs) BIB001 ,  exploit the collision resistance property to provide message authentication, which ensures the integrity of the transmitted data. The message to be transmitted, along with a shared secret, is hashed to produce a message authentication code (MAC) which can be used at the receiver side to verify that the message has not been altered. The inclusion of the shared secret, in fact, prevents an attacker from simply replacing the whole message-MAC pair, since the latter cannot be computed without knowing the shared secret. It has been proved that HMAC is directly and formally related with the security of the hash function employed BIB001 . HMACs are employed by the IPSec protocol  , both in the Authentication Header (AH)  and in the Encapsulated Security Payload (ESP)  modes. Pseudo-Random Number Generators (PRNGs) based on Deterministic Random Bit Generation (DRBG)  produce pseudo-random sequences by hashing a linearly increasing seed. In addition to cryptographic hash functions, PRNGs can also be built from HMACs  . Most of the security protocols listed above are standardized by NIST  ,  ,  , which requires the underlying hash function to be one of its approved hash functions. However, vulnerabilities have been found in SHA-1 BIB004 , leading eventually to its breaking  . Given that alternative hash functions such as MD5  were already known to be broken BIB005 , BIB006 , SHA-2 has been the only viable alternative for many years. Although a new hash function, SHA-3, has been standardised by NIST in 2015  , it has not reached widespread diffusion yet. Considering the slow process that has taken place for SHA-2 to fully replace SHA-1  , along with the fact that there are no significant vulnerabilities to SHA-2, the new SHA-3 function is not expected to replace SHA-2 in the near future. Moreover, SHA-3 is based on a completely different mathematical construction than SHA-2. While the different nature of the function makes it difficult to re-use the body of knowledge in SHA-2 and SHA-1 cryptanalysis, more study is still required to increase confidence in the cryptographic strength of the new SHA-3 function BIB007 . On the other hand, SHA-2 has undergone intense cryptanalysis BIB003 for more than 15 years, and no weaknesses have been found yet, making SHA-2 attractive for emerging applications where long-term collision resistance is required.