Abstract: Bucketized versions of Cuckoo hashing can achieve 95-99% occupancy, without any space overhead for pointers or other structures. However, such methods typically need to consult multiple hash buckets per probe, and have therefore been seen as having worse probe performance than conventional techniques for large tables. We consider workloads typical of database and stream processing, in which keys and payloads are small, and in which a large number of probes are processed in bulk. We show how to improve probe performance by (a) eliminating branch instructions from the probe code, enabling better scheduling and latency-hiding by modern processors, and (b) using SIMD instructions to process multiple keys/payloads in parallel. We show that on modern architectures, probes to a bucketized Cuckoo hash table can be processed much faster than conventional hash table probes, for both small and large memory-resident tables. On a Pentium 4, a probe is two to four times faster, while on the Cell SPE processor a probe is ten times faster.

Abstract: A system and method for efficiently backing up and restoring computer files to a central storage system. A hashing key is computed for each file to be backed up on a target computer. The hashing key is compared to a list of hashing keys stored locally to see if the local file has been previously backed up. If the hashing key is not listed locally, then the hashing key is compared to a list of hashing keys of centrally backed up files. Only if the hashing key is not present in both the local and the central list is the file backed up. Backed up files may be renamed to their hashing key for further efficiencies.

Abstract: An image hash is a randomized compact representation of image content and finds applications in image authentication, image and video watermarking, and image similarity comparison. Usually, an image-hashing scheme is required to be robust and secure, and the security issue is particularly important in applications, such as multimedia authentication, watermarking, and fingerprinting. In this paper, we investigate the security of image hashing from the perspective of unicity distance, a concept pioneered by Shannon in one of his seminal papers. Using two recently proposed image-hashing schemes as representatives, we show that the concept of unicity distance can be adapted to evaluate the security of image hashing. Our analysis shows that the secret hashing key, or its equivalent form, can be estimated with high accuracy when the key is reused several dozen times. The estimated unicity distance determines the maximum number of key reuses in the investigated hashing schemes. A countermeasure of randomized key initialization is discussed to avoid key reuse and strengthen the security of robust image hashing.

Abstract: We present a new, efficient and easy to use collision detection scheme for real-time collision detection between highly deformable tetrahedral models. Tetrahedral models are a common representation of volumetric meshes which are often used in physically based simulations, e.g. in Virtual surgery. In a deformable models environment collision detection usually is a performance bottleneck since the data structures used for efficient intersection tests need to be rebuilt or modified frequently. Our approach minimizes the time needed for building a collision detection data structure. We employ an infinite hierarchical spatial grid in which for each single tetrahedron in the scene a well fitting grid cell size is computed. A hash function is used to project occupied grid cells into a finite ID hash table. Only primitives mapped to the same hash index indicate a possible collision and need to be checked for intersections. This results in a high performance collision detection algorithm which does not depend on user defined parameters and thus flexibly adapts to any scene setup.

Abstract: Cuckoo hashing combines multiple-choice hashing with the power to move elements, providing hash tables with very high space utilization and low probability of overflow. However, inserting a new object into such a hash table can take substantial time, requiring many elements to be moved. While these events are rare and the amortized performance of these data structures is excellent, this shortcoming is unacceptable in many applications, particularly those involving hardware router implementations. We address this difficulty, focusing on the potential of content-addressable memories and queueing techniques to provide a de-amortization of cuckoo hashing suitable for hardware, and in particular for high-performance routers.

Abstract: Embodiments include methods, apparatus, and systems for virtual address hashing. One embodiment evenly distributes page-table entries throughout a hash table so applications do not generate a same hash index for mapping virtual addresses to physical addresses.

Abstract: Methods and apparatus, including computer program products, implementing and using techniques for generating a hash. A data store including multiple hashing tables is provided. A set of data is received on which the hash is to be based. The set of data includes one or more components. An identifier is received. The identifier identifies one or more hashing tables to use when generating the hash. The received one or more components are processed in accordance with rules defined in the identified one or more hashing tables. The processed components are combined into a final hash.

Abstract: In RFID system, the problem of the collision between tags is a focus topic. The Hash-tree anti-collision algorithm was proposed in the paper, which adopted hash operation to allocate slots for tags and used tree searching method to identify collision tags in the queue of collision slots. The proposed algorithm doesn't require readers to test the precise location of collision bits, and its performance beyond 36.8% is better than ALOHA- based algorithms.

Abstract: It is known that when searching the table for data,comparison is made with the keyword which exit in the table.In another word,comparison is the base of common searching method in finding out the data.Such methods are: Sequential Search,Binary Search and Binary Sort Tree Search.But the efficiency of these methods depends on the times of comparisons made.Even more,sometimes data in the bad sector takes a long time to finish the comparison.The ideal method is the one that needs no comparison in the process of searching;and this ideal goal can be achieved by application of the Hash Table.

Abstract: At Eurocrypt'05, Wang et al presented efficient collision attacks on MD5 and MD4 hash functions They found a collision of MD5 with a complexity of less than 237 MD5 hash operations, and a collision of MD4 with complexity less than 28 MD4 hash operations In their attack, the procedure to generate a collision is divided into 4 steps First, they determine the message differential and output differentials of chaining variables in each step, which generates a collision with small complexity Second, they construct sufficient conditions that guarantee that the desired differential is always calculated Third, they find a message modification that can satisfy the sufficient conditions with high probability Finally, they search for a message that satisfies all sufficient conditions In this paper, we focus on the message modification of MD5 and MD4, and propose a new message modification Using our message modification, a collision of MD5 can be found with complexity less than 229 MD5 hash operations, and a collision of MD4 can be found with complexity less than 3 MD4 hash operations To improve the complexity from previous attacks, we mainly use two ideas The first idea is to use message modification that can satisfy more sufficient conditions in the second round than in previous attacks The second idea is to use message modification that can enable us to search for a collision starting from an intermediate step