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.
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.
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.
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.
500553
Making register file resistant to power analysis attacks
Power analysis attacks are a type of side-channel attacks that exploits the power consumption of computing devices to retrieve secret information. They are very effective in breaking many cryptographic algorithms, especially those running in low-end processors in embedded systems, sensor nodes, and smart cards. Although many countermeasures to power analysis attacks have been proposed, most of them are software based and designed for a specific algorithm. Many of them are also found vulnerable to more advanced attacks. Looking for a low-cost, algorithm-independent solution that can be implemented in many processors and makes all cryptographic algorithms secure against power analysis attacks, we start with register file, where the operands and results of most instructions are stored. In this paper, we propose RFRF, a register file that stores data with a redundant flipped copy. With the redundant copy and a new precharge phase in write operations, RFRF provides data-independent power consumption on read and write for cryptographic algorithms. Although RFRF has large energy overhead, it is only enabled in the security mode. We validate our method with simulations. The results show that the power consumption of RFRF is independent of the values read out from or written to registers. Thus RFRF can help mitigate power analysis attacks.
14334349
Learning Cascaded Reduced-Set SVMs Using Linear Programming
This paper proposes a simple and efficient detection framework that uses reduced-set kernels. We first describe our approach which reduces the number of kernels. A convex optimization method is used for calculating the reduced sets. Following this, we propose a method that optimally designs the cascade. Our experimental results indicate that our method minimizes complexity regarding the number of kernels in the cascaded structure while preserving the low error rates. Our algorithm generates the optimal weight of kernels for each cascade stage. This proposed algorithm achieves high detection-rates at low computational cost.
31834649
A Novel Artificial Immune Network Model and Analysis on Its Dynamic Behavior and Stabilities
A novel model of artificial immune network is presented at first, and then a simulative research work is made on its dynamic behaviors. Simulation results show that the limit cycle and chaos may exist simultaneously when four units are in connection, and the network's characteristic has a close relationship with the intensity of suppressor T-cell's function, B-cell's characteristics and transconductance. Besides this, with Liapunov's method, the sufficient conditions for network's stability is studied, especially for the case of system's characteristics under the condition that the helper T-cells appear as a nonlinear function.
33446676
Voronoi Tessellation Based Rapid Coverage Decision Algorithm for Wireless Sensor Networks
The coverage problem is a fundamental issue in the research of sensor network. A novel Voronoi tessellation based rapid coverage decision algorithm is proposed, in which the region of interest is partitioned into some square grids firstly, and then the complex area coverage problem is transformed into simple vertices coverage problem, on the basis of the good characteristics of Voronoi tessellation such as being able to divide the planner area into a set of simple geometric simplexes. Theoretical analysis and simulation results show that, the new algorithm can decrease the computation complexity of networks, especially for sensor networks with n different sensors, it can solve the coverage problem correctly for any given region of interest with time costs of O(nlogn) only.
34620301
Video Local Pattern based Image Matching for Visual Mapping
Image matching plays an important role in visual mapping, a critical task of vision based mobile robot navigation. Based on the observation that the visual content in these video sequences generally changes in a slow and continuous mode, a concept of "video local pattern" is proposed to model each video frame, which is defined as a set of frames that are visually-similar and temporally-adjacent to that frame. Instead of manually labelling, a tracking based method is developed to automatically detect the local pattern for each frame. A model is then estimated from a local pattern, and the matching of images is performed by comparing these models. Experimental results demonstrated its improvement over that comparing individual frames