8484163
Near-Collision Attacks on MD4: Applied to MD4-Based Protocols
The most widely used hash functions from MD4 family have been broken, which lead to a public competition on designing new hash functions held by NIST. This paper focuses on one concept called near-collision resistance: computationally difficult to find a pair of messages with hash values differing in only few bits, which new hash functions should satisfy. In this paper, we will give a model of near-collisions on MD4, and apply it to attack protocols including HMAC/NMAC-MD4 and MD4(Password||Challenge). Our new outer-key recovery attacks on HMAC/NMAC-MD4 has a complexity of 272 online queries and 277 MD4 computations, while previous result was 288 online queries and 295 MD4 computations. Our attack on MD4(Password||Challenge) can recover 16 password characters with a complexity of 237 online queries and 221 MD4 computations, which is the first approach to attack such protocols.
20187054
Bit-Free Collision: Application to APOP Attack
This paper proposes a new variant of collisions on hash functions named bit-free collision , which can be applied to reduce the number of chosen challenges in password recovery attacks on hash-based challenge and response protocols, such as APOP (Authentication Post Office Protocol). In all previous APOP attacks, the attacker needs to impersonate the server and to send poisoned chosen challenges to the user. Impersonating the server takes a risk that the user may find out he is being attacked. Hence, it is important for the attacker to reduce the number of impersonation in order to lower the probability that the attack will be detected. To achieve this, reducing the number of chosen challenges is necessary. This paper is the first approach to improve previous APOP attacks based on this observation to our best knowledge. With t -bit-free collisions presented in this paper, the number of chosen challenges to recover each password character can be reduced by approximately a factor of 2 t . Though our attack utilizing t -bit-free collisions needs higher offline complexity than previous attacks, the offline computation can be finished in practical time if the attacker can obtain reasonable computation power. In this research, we generate 1-bit-free collisions on MD5 practically. As a result, the number of challenges for password recovery attacks on real APOP is approximately half reduced. Of independent interest, we apply the bit-free-collision attack on a simpler hash function MD4, and show that 3-bit-free collisions can be generated practically.
31093950
Extended Password Recovery Attacks against APOP, SIP, and Digest Authentication
In this paper, we propose password recovery attacks against challenge-response authentication protocols. Our attacks use a message difference for a MD5 collision attack proposed in IEICE 2008. First, we show how to efficiently find a message pair that collides with the above message difference. Second, we show that a password used in authenticated post office protocol (APOP) can be recovered practically. We also show that the password recovery attack can be applied to a session initiation protocol (SIP) and digest authentication. Our attack can recover up to the first 31 password characters in a short time and up to the first 60 characters faster than the naive search method. We have implemented our attack and confirmed that 31 characters can be successfully recovered.
37423199
How to Confirm Cryptosystems Security: The Original Merkle-Damgård Is Still Alive!
At Crypto 2005, Coron et al. showed that Merkle-Damgard hash function (MDHF) with a fixed input length random oracle is not indifferentiable from a random oracle RO due to the extension attack. Namely MDHF does not behave like RO. This result implies that there exists some cryptosystem secure in the RO model but insecure under MDHF. However, this does not imply that no cryptosystem is secure under MDHF. This fact motivates us to establish a criteria methodology for confirming cryptosystems security under MDHF. 
 
In this paper, we confirm cryptosystems security by using the following approach: 1 Find a variant, $\widetilde{\mathsf{RO}}$, of RO which leaks the information needed to realize the extension attack. 
 1 Prove that MDHF is indifferentiable from $\widetilde{\mathsf{RO}}$. 
 1 Prove cryptosystems security in the $\widetilde{\mathsf{RO}}$ model. 
 From the indifferentiability framework, a cryptosystem secure in the $\widetilde{\mathsf{RO}}$ model is also secure under MDHF. Thus we concentrate on finding $\widetilde{\mathsf{RO}}$, which is weaker than RO. 
 
We propose the Traceable Random Oracle (TRO) which leaks enough information to permit the extension attack. By using TRO, we can easily confirm the security of OAEP and variants of OAEP. However, there are several practical cryptosystems whose security cannot be confirmed by TRO (e.g. RSA-KEM). This is because TRO leaks information that is irrelevant to the extension attack. Therefore, we propose another $\widetilde{\mathsf{RO}}$, the Extension Attack Simulatable Random Oracle, ERO, that leaks just the information needed for the extension attack. Fortunately, ERO is necessary and sufficient to confirm the security of cryptosystems under MDHF. This means that the security of any cryptosystem under MDHF is equivalent to that under the ERO model. We prove that RSA-KEM is secure in the ERO model.
10157835
New Message Differences for Collision Attacks on MD4 and MD5
In 2005, collision resistance of several hash functions was broken by Wang et al. The strategy of determining message differences is the most important part of collision attacks against hash functions. So far, many researchers have tried to analyze Wang et al.'s method and proposed improved collision attacks. Although several researches proposed improved attacks, all improved results so far were based on the same message differences proposed by Wang et al. In this paper, we propose new message differences for collision attacks on MD4 and MD5. Our message differences of MD4 can generate a collision with complexity of less than two MD4 computations, which is faster than the original Wang et al.'s attack, and moreover, than the all previous attacks. This is the first result that improves the complexity of collision attack by using different message differences from Wang et al.'s. Regarding MD5, so far, no other message difference from Wang et al.'s is known. Therefore, study for constructing method of other message differences on MD5 should be interesting. Our message differences of MD5 generates a collision with complexity of 242 MD5 computations, which is slower than the latest best attack. However, since our attack needs only 1 bit difference, it has some advantages in terms of message freedom of collision messages.
16195917
New Key-Recovery Attacks on HMAC/NMAC-MD4 and NMAC-MD5
At Crypto '07, Fouque, Leurent and Nguyen presented full key-recovery attacks on HMAC/NMAC-MD4 and NMAC-MD5, by extending the partial key-recovery attacks of Contini and Yin from Asiacrypt '06. Such attacks are based on collision attacks on the underlying hash function, and the most expensive stage is the recovery of the socalled outer key. In this paper, we show that the outer key can be recovered with near-collisions instead of collisions: near-collisions can be easier to find and can disclose more information. This improves the complexity of the FLN attack on HMAC/NMAC-MD4: the number of MAC queries decreases from 288 to 272, and the number of MD4 computations decreases from 295 to 277. We also improved the total complexity of the related-key attack on NMAC-MD5. Moreover, our attack on NMAC- MD5 can partially recover the outer key without the knowledge of the inner key, which might be of independent interest.
25158433
Diagnosis of delay faults due to resistive bridges, delay variations and defects
In this paper, we present the first diagnosis algorithm for combinational circuit blocks that considers all combinations of multiple gate/wire delay variations/defects and any single resistive bridge. One key component of the proposed algorithm is a new path-oriented effect-cause procedure to identify all possible suspects of above type that might have caused the timing errors observed during test. The second key component is an efficient data structure to represent the suspects. The third key component is a new algorithm to analyze passing tests to vindicate some of the suspects identified. This algorithm exploits the newly identified concept of fixed-but-unknown delays, i.e., the fact that during the period of diagnosis the values of all delay parameters for every gate and wire in the particular circuit under test remain fixed, although at values unknown to us. The final set of suspects reported by the algorithm is guaranteed to contain all possible causes of the observed timing errors. Experimental results on benchmark circuits show the effectiveness of the proposed approach
17996623
Fault tolerant scheduling for fixed-priority tasks with preemption threshold
Fixed-priority with preemption threshold (FPPT) is an important form of real-time scheduling algorithm, which fills the gap between fixed-priority preemptive (FPP) and fixed-priority non-preemptive (FPNP). However, this scheduling scheme together with the requirements of fault tolerance makes the prediction of a real-time system's behaviors more difficult than traditional scheduling scheme. The major contribution of this work is twofold. First, we present an appropriate schedulability analysis, based on response time analysis, for supporting fault-tolerant FPPT scheduling in hard real-time systems. The error-recovery techniques are considered to be used to carry out fault tolerance. Second, we propose the optimal priority assignment algorithm which can be used, together with the schedulability analysis, to improve system fault resilience.
8968963
Offense based temporal segmentation for event detection in soccer video
Sports video is regarded as a good testing bed for techniques on content based video analysis and processing. Although partially successful systems have been designed for specific sports domains with limited data, most previous works do not adequately address the problem of temporal segmentation for event detection, nor the event representation problem. In this paper, we present an analysis of soccer video for detecting the semantic notion of <i>offense</i>. It is not only useful as a new semantic concept of sports video analysis, but also provides temporal segmentation for video event detection and representation. We propose a system to detect the offensive unit in soccer video automatically. The offensive unit is then used to calculate new semantics like <i>possession</i>, as well as to detect goal events in video. Experimental results on various sources of soccer video have verified that our approach extracts the new semantic notions successfully and facilitates video event detection and representation
29743973
SVM Model Based on Signal Transformation and its Applications in Oil Water-Flooded Identification
this paper, a method of signal transformation for feature extraction is proposed. It can transform log-signal space into the vector space, which the experiment system requires, and then use SVM (Support Vector Machine) automatically to identify the water-flooded status of oil-saturated stratum. The results of experiment indicate that this algorithm has good identification ability and strong generalization ability in condition that the number of training swatch is limited.
31999867
A Novel Classifier with the Immune-Training Based Wavelet Neural Network
After analyzing the classification and training ability of a wavelet neural network (WNN), a novel WNN learning scheme integrating immunity based evolutionary algorithm (IDEA) is proposed, in which, IDEA is an evolutionary algorithm with an embedded immune mechanism. When WNN is used as a classifier, the process of seeking the least mean-square error (LMS) of an optimal problem is equivalent to that of finding the wavelet feature with maximal separability, namely, maximizing its separable division. On the other hand, with the capability of robust learning of its evolutionary process, IDEA is able to eliminate local degenerative phenomenon due to blindfold behaviors of original operators in the existing evolutionary algorithms. In the case of the twin-spiral problem, experimental simulation shows the feasibility of WNN training with the IDEA based learning algorithm.