Usually, a proof of a theorem contains more knowledge than the mere fact that the theorem is true. For instance, to prove that a graph is Hamiltonian it suffices to exhibit a Hamiltonian tour in it; however, this seems to contain more knowledge than the single bit Hamiltonian/non-Hamiltonian.In this paper a computational complexity theory of the “knowledge” contained in a proof is developed. Zero-knowledge proofs are defined as those proofs that convey no additional knowledge other than the correctness of the proposition in question. Examples of zero-knowledge proof systems are given for the languages of quadratic residuosity and 'quadratic nonresiduosity. These are the first examples of zero-knowledge proofs for languages not known to be efficiently recognizable.

/pdf/the-knowledge-complexity-of-interactive-proof-systems-31apre0ecf.pdf

The knowledge complexity of interactive proof-systems

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.

/pdf/finding-collisions-in-the-full-sha-1-ptij2r5weq.pdf

Finding collisions in the full SHA-1

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.

/pdf/how-to-break-md5-and-other-hash-functions-44gqgi9bi5.pdf

How to break MD5 and other hash functions

Security is an essential service for wired and wireless network communications. The success of mobile ad hoc network (MANET) will depend on people ’s confidence in its security. However, the characteristics of MANET pose both challenges and opportunities in achieving security goals, such as confidentiality, authentication, integrity, availability, access control, and non-repudiation. We provide a survey of attacks and countermeasures in MANET in this chapter. The countermeasures are features or functions that reduce or eliminate security vulnerabilities and attacks. First, we give an overview of attacks according to the protocol layers, and to security attributes and mechanisms. Then we present preventive approaches following the order of the layered protocol layers. We also put forward an overview of MANET intrusion detection systems (IDS), which are reactive approaches to thwart attacks and used as a second line of defense.

A Survey of Attacks and Countermeasures in Mobile Ad Hoc Networks

An important open problem in the area of Traitor Tracing is designing a scheme with constant expansion of the size of keys (users' keys and the encryption key) and of the size of ciphertexts with respect to the size of the plaintext. This problem is known from the introduction of Traitor Tracing by Chor, Fiat and Naor. We refer to such schemes as traitor tracing with constant transmission rate. Here we present a general methodology and two protocol constructions that result in the first two public-key traitor tracing schemes with constant transmission rate in settings where plaintexts can be calibrated to be sufficiently large. Our starting point is the notion of copyrighted function which was presented by Naccache, Shamir and Stern. We first solve the open problem of discrete-log-based and public-key-based copyrighted function. Then, we observe the simple yet crucial relation between (public-key) copyrighted encryption and (public-key) traitor tracing, which we exploit by introducing a generic design paradigm for designing constant transmission rate traitor tracing schemes based on copyrighted encryption functions. Our first scheme achieves the same expansion efficiency as regular ElGamal encryption. The second scheme introduces only a slightly larger (constant) overhead, however, it additionally achieves efficient black-box traitor tracing (against any pirate construction).

Traitor Tracing with constant transmission rate

In this paper, we present an improvement of the Nguyen-Vidick heuristic sieve algorithm for shortest vector problem in general lattices, which time complexity is 20.3836n polynomial computations, and space complexity is 20.2557n. In the new algorithm, we introduce a new sieve technique with two-level instead of the previous one-level sieve, and complete the complexity estimation by calculating the irregular spherical cap covering.

/pdf/improved-nguyen-vidick-heuristic-sieve-algorithm-for-ye0to5zite.pdf

Improved Nguyen-Vidick heuristic sieve algorithm for shortest vector problem

In Eurocrypt’05, Wang et al. presented new techniques to find collisions of Hash function MD4. The techniques are not only efficient to search for collisions, but also applicable to explore the second- preimage of MD4. About the second-preimage attack, they showed that a random message was a weak message with probability 2−122 and it only needed a one-time MD4 computation to find the second-preimage corresponding to the weak message. A weak message means that there exits a more efficient attack than the brute force attack to find its second-preimage. In this paper, we find another new collision differential path which can be used to find the second-preimage for more weak messages. For any random message, it is a weak message with probability 2−56, and it can be converted into a weak message by message modification techniques with about 227 MD4 computations. Furthermore, the original message is close to the resulting message (weak message), i.e, the Hamming weight of the difference for two messages is about 44.

The second-preimage attack on MD4

In this paper, we present the first distinguishing attack on HMAC and NMAC based on MD5 without related keys, which distinguishes the HMAC/NMAC-MD5 from HMAC/NMAC with a random function. The attack needs 297 queries, with a success probability 0.87, while the previous distinguishing attack on HMAC-MD5 reduced to 33 rounds takes 2126.1 messages with a success rate of 0.92. Furthermore, we give distinguishing and partial key recovery attacks on MDx -MAC based on MD5. The MDx -MAC was proposed by Preneel and van Oorschot in Crypto'95 which uses three subkeys derived from the initial key. We are able to recover one 128-bit subkey with 297 queries.

/pdf/cryptanalysis-on-hmac-nmac-md5-and-md5-mac-2qe7kaonz0.pdf

Cryptanalysis on HMAC/NMAC-MD5 and MD5-MAC

Reference EPFL-REPORT-164541 URL: http://eprint.iacr.org/2005/067 Record created on 2011-03-29, modified on 2017-05-12

/pdf/colliding-x-509-certificates-3m4qvclh16.pdf

Colliding X.509 certificates

1Key Laboratory of Cryptologic Technology and Information Security, Ministry of Education, Shandong University, Jinan 250100, China; 2School of Mathematics, Shandong University, Jinan 250100, China; 3Institute for Advanced Study, Tsinghua University, Beijing 100084, China; 4Department of Computer Science and Technology, Tsinghua University, Beijing 100084, China; 5Beijing Research Institute of Telemetry, Beijing 100094, China

Xiaoyun Wang

Papers

Improved Nguyen-Vidick heuristic sieve algorithm for shortest vector problem

The second-preimage attack on MD4

Cryptanalysis on HMAC/NMAC-MD5 and MD5-MAC

Colliding X.509 certificates

Differential attacks on reduced SIMON versions with dynamic key-guessing techniques