From this generalization it can be assumed that the performance of hash functions and comparisons between other hash functions can be determined by modeling the functions as PRNGs. Analysis techniques such a Poisson distribution can be used to analyze the collision rates of different hash functions for different groups of data. In general there is a theoretical hash function known as the Perfect Hash Function for any specific group of data. The perfect hash function by definition states that no collisions will occur meaning no repeating hash values will arise from different elements of hybrid Cryptography with examples in Ruby and Go group.
In reality it is very difficult to find a perfect hash function for an arbitrary set of data, and furthermore the practical applications of perfect hashing and its variant minimal perfect hashing are quite limited. So instead one may choose to pursue the concept of an Ideal Hash Function, which is commonly defined as a function that produces the least amount of collisions for a particular set of data. One of the fundamental problems with hashing data or specifically mapping values from one domain to another, is that there are soo many permutations of types of data, some highly random, others containing high degrees of patterning or structure that it is difficult to generalize a hash function for all data types or even for specific data types. Each message is hashed using two different hash functions H1 and H2.
H2 returns the same value for each message causing numerous collisions. A hash function should in theory be a very quick, stable and deterministic operation. The hash functions in this essay are known as simple hash functions or General Purpose Hash Functions. They are used to create keys which are used in associative containers such as hash-tables. These hash functions are not cryptographically safe, they can easily be reversed and many different combinations of data can be easily found to produce identical hash values for any combination of data.
A simplified version of this method can be used to easily generate well performing general purpose hash functions. Note: The term Finalize means to take the internal state and prepare the final hash value that will be returned from the function. In the event the IS contains more bits than is required for the hash value, the IS itself will undergo a mixing process that will result in a value that is size compatible with the hash value type. The “Mix” operation denoted above takes as input the internal state and the current message block, performs some computation and returns the value of the internal state.
Putting it all together requires looping over all of the message 32-bits at-a-time, performing the mix operation upon each block, updating the internal state and taking care of any remainder bits after the main loop has completed. In the mix process defined above there are two static values 2 and 3, being used – if one where to utilize a LUT of values, then perhaps as an example a different value can be used on each round, rather than just the values 2 and 3 for each and every round. In the design of cryptographic hash functions and ciphers, the construction of S-Boxes and P-Boxes have become a well studied area. If one is looking to implement a general purpose hash function based on utilizing a list of values during the mixing process, a review of the literature associated with S-Box and P-Box design techniques would be highly recommendable. Recommendation 1: The “mix” operation does not need to be the same on each round. There could be multiple mix operations which are selected based on criteria such as the index of the current round, the value of the internal state etc.
Recommendation 2: When hashing large messages, one could break the message up into chunks and compute the hash of each chunk in parallel then aggregate the hashes using a mix operation, this will dramatically increase the throughput of the hash function when running upon architectures that support multiple cores. This method of hashing is known as a Merkle-Tree or a hash-tree. Recommendation 3: The operations present in the Mix should be carefully chosen, as more often than not the mixing process may result in lowering the entropy of the internal state to the point where the internal state does not change. As an example in the mix operation denoted above if the internal state reaches the value ZERO it will typically end-up returning zero. Recommendation 4: The mix operation should handle repeated values in the message block, without causing a “flush effect on the internal state. A typical scenario might be a message comprised of bytes with the value of zero.
Question: how many consecutive zero bytes will it take to get the internal state of the hash function to become zero? The answer for a well designed hash function should be: A-LOT. This is due to the fact that the pointers will be storing addresses that are multiples of either 4 or 8 depending on the machine’s addressing granularity. The problems that arise here are typically related to the Pigeonhole Principle.
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When using a hash function as part of a hash-table, one will want to quantize or in other words reduce the hash value to be within the range of the number of buckets in the hash-table. It is assumed that a good hash functions will map the message m within the given range in a uniform manner. The problem, assuming uniformly distributed keys in the range , is that the buckets will have a higher probability of having values mapped to them when compared to the other buckets in the range . Simply put this particular problem can’t be resolved by using prime numbers as the quantisation value. Note: This problem also appears when generating random numbers within a specified range, where the underlying random number generator generates values in a range that is larger than and is not a multiple of the desired range.
N is the number of buckets in a hash table and as such is commonly used as the quantisation value. There is an issue which can arise if the keys being hashed are not uniformly distributed. Specifically when the keys result in values before quantisation that are factors or multiples of factors of N. This situation seems to be the only valid reason to use a prime number as a quantisation value. One further thing to consider would be that instead of a prime number we could have chosen a composite number that does not have three as one of its factors. But we would then also have to guarantee that none of the multiples of three, which we intend to quantise, are also not one of its factors – in short the problem becomes very hairy very quickly for little to no gain – Q.
That being said, this particular solution has a slight overhead of its own – that is once a maximum table load factor has been reached the table will need to be re-sized. This is typically achieved by simply doubling the size of the current table, but one must also remember to snap to the next largest prime number as the new size, rather than simply doubling the current size. In conclusion it would be far more productive and effective to mix the keys more thoroughly and rigorously than it would be to faff around with the ever changing quantisation parameter. In implementing the mixing operation, one tries to define a process where by all the bits of the message block, equally affect all the bits of the internal state.
It just seems to be an ongoing self-proclaimed intuition that some professionals in the field seem obliged to follow and preach. Example: Let’s assume a PRNG that produces 8-bit blocks as its output. From this one concludes that even though there are 256 possible values that can be produced with this PRNG, values less than 128 will never be generated. All PRNGs, be they the likes of hash functions, ciphers, m-sequences or anything else that produces a bit sequence will all exhibit some form of bit bias.
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Most PRNGs will attempt to converge their bit biases to an equality, stream ciphers are one example, whereas others will work best with a known yet unstable bit bias. Mixing or scrambling of a bit sequence is one way of producing a common equality in the bit bias of a stream. Though one must be careful to ensure that by mixing they do not further diverge the bit biases. As displayed in the figure below the avalanching process begins with one or more pieces of binary data.
1’th tier data where the number of bits in the current tier will be less than or equal to the number of bits in the previous tier. It should be noted that the figure below is a mere generalisation of the avalanching process and need not necessarily be the only form of the process. Below are some of the more common uses of hash functions. A strong cryptographic hash function has the property of being very difficult to reverse the result of the hash and hence reproduce the original piece of data. Cryptographic hash functions are used to hash user’s passwords and have the hash of the passwords stored on a system rather than having the password itself stored. The process involves initially selecting a region or object of interest.
This set is sometimes called a macro-feature or a constellation of features. A hash value is computed from the constellation of features. This is typically done by initially defining a space where the hash values are intended to reside – the hash value in this case is a multidimensional value normalized for the defined space. Typical examples of geometric hashing include the classification of various kinds of automobiles, for the purpose of re-detection in arbitrary scenes. The level of detection can be varied from just detecting a vehicle, to a particular model of vehicle, to a specific vehicle. In computer science this is known as a membership query and is a core concept in associative containers.
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The guarantee a Bloom filter provides is that for any membership query there will never be any false negatives, however there may be false positives. Subsequent research done in the area of hash functions and their use in bloom filters by Mitzenmacher et al. Each range is associated with one or more nodes, which hold values for keys that hash into that address range. This replication is done to provide resilience against node failures and allow for load balancing and overall latency reductions when data that hashes to a particular node is highly sought after or queried by many clients. The following algorithms vary in usefulness and functionality and are mainly intended as an example for learning how hash functions operate and what they basically look like in code form. I’ve added some simple optimizations to the algorithm in order to speed up its hashing process.
Aho, Sethi and Ulman, recommends the use of hash functions that employ the hashing methodology found in this particular algorithm. It is a widley used hash function on UNIX based systems. It is a simple hash function using a strange set of possible seeds which all constitute a pattern of 31. 3131 etc, it seems to be very similar to the DJB hash function. 31 131 1313 13131 131313 etc. The hash function seems to have a good over-all distribution for many different data sets. It seems to work well in situations where there is a high variance in the MSBs of the elements in a data set.
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Bernstein and shown first to the world on the usenet newsgroup comp. It is one of the most efficient hash functions ever published. Knuth in The Art Of Computer Programming Volume 3, under the topic of sorting and search chapter 6. I took ideas from all of the above hash functions making a hybrid rotative and additive hash function algorithm. There isn’t any real mathematical analysis explaining why one should use this hash function instead of the others described above other than the fact that I tired to resemble the design as close as possible to a simple LFSR. No more missed important software updates! The database recognizes 1,746,000 software titles and delivers updates for your software including minor upgrades.
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The reduced-price devices are not returnable, according to the email. HP originally acquired webOS as part of its takeover of Palm in 2010. The manufacturer originally had big plans for loading the operating system onto a variety of devices, including tablets, smartphones, desktops and laptops. 99, which sparked a surge of consumer interest. In the wake of that, HP made the decision to revive the line for a limited time. In addition, HP plans on dividing its webOS arm into two separate units reporting to different areas of the company, according to two leaked memos that have made their way onto the Web. The webOS software assets will find their way into the arms, however welcoming, of its Office of Strategy and Technology.
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Feedback forms will be available at the show. Let us know who was hot, who was not and get a chance to win admission to a future Briefings of your choice. To those who seek truth through science, even when the powerful try to suppress it. Until his retirement in January 2003, Mr. Clarke was a member of the Senior Executive Service. He served as an advisor to four U.
1973 to 2003: Ronald Reagan, George H. Bush, Bill Clinton and George W. Group, part of the Information Assurance Directorate at the National Security Agency. The mission of the VAO organization is to identify, characterize, and put into operational context vulnerabilities found in the technology, information, and operations of the DoD and the national security community and to help the community identify countermeasures and solutions. Security is both a feeling and a reality.
You can feel secure without actually being secure, and you can be secure even though you don’t feel secure. In the industry, we tend to discount the feeling in favor of the reality, but the difference between the two is important. It explains why we have so much security theater that doesn’t work, and why so many smart security solutions go unimplemented. CTO of BT Counterpane, referred to by The Economist as a “security guru. His influential newsletter, Crypto-Gram, and blog “Schneier on Security,” are read by over 250,000 people. A Dangling Pointer is a well known security flaw in many applications.
In some scenarios, the developer may accidentally use a pointer to an invalid object. In such a case, the application will enter an unintended execution flow which could lead to an application crash or other types of dangerous behaviors. Watchfire, a market-leading provider of software and service to help ensure the security and compliance of websites. Jonathan specializes in network and web application security, reverse engineering and exploit development. Fuzz it Like you Mean it! Even the most expensive commercial fuzzing suites leave much to be desired by way of automation.
Perhaps the reason for this is that even the most rudimentary fuzzers are surprisingly effective. None the less, if you are serious about fuzz testing in as much a scientific process as possible than you have no doubt been disappointed with the current state of affairs. An open source, freely available, full featured and extensible fuzzing framework being released at Black Hat US 2007. Modern day fuzzers are, for the most part, solely focused on data generation. Sulley does this better and more. Sulley watches the network and methodically maintains records.
Sulley instruments and monitors the health of the target, capable of reverting to a good state using multiple methods. In conjunction with his passion for the field, he launched OpenRCE. Pedram holds a computer science degree from Tulane University, finds his current commander in chief rather humerous and recently co-authored a book on Fuzzing titled “Fuzzing: Brute Force Vulnerability Discovery”. His responsibilities include reverse engineering, vulnerability discovery, and tool development. Aaron has discovered critical vulnerabilities affecting a wide range of enterprise vendors including: RSA, Citrix, Symantec, Hewlett-Packard, IBM and others. Virtualization is changing how operating systems function and how enterprises manage data centers. This talk will focus on security model of the system, with emphasis on design choices and deployment considerations.
Aspects of virtualization security related to hardware functions will also be explored. For the past five years he has worked on security and separation kernels at Microsoft of one form or another. Baker was a security architect at a managed data center company. Injecting RDS-TMC Traffic Information Signals a. Founder and Chief Security Engineer, Inverse Path Ltd. FM radio Traffic Information for Satellite Navigation Systems.
All modern in-car Satellite Navigation systems sold in Europe use RDS-TMC to receive broadcasts containing up to date information about traffic conditions such as queues and accidents and provide detours in case they affect the plotted course. The system is increasingly being used around Europe and North America. PC and cheap home-made electronics, with the intent of injecting information in the broadcast RDS-TMC stream manipulating the information displayed by the satellite navigator. In order to maximize the presentation we’ll also demo the injectionhopefully at low power so that we won’t piss off local radio broadcasts.
His professional career began 8 years ago but all really started when a Commodore-64 first arrived in his home when he was 10. Firewalls deployment and administration, forensic analysis, vulnerability assessment, penetration testing, security training and his Open Source projects. In this talk, we will discuss the challenges faced by digital investigators in solving electronic crime committed by knowledgeable insiders. These challenges will be presented in light of three real world investigations conducted by the presenters.
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The first case is the high-profile U. Duronio trial, in which Keith Jones testified as the DoJ’s computer forensics expert. Jones testified for over five days about how Mr. His testimony was key in the prosecution of the accused on charges of securities fraud and electronic crime.
The second incident involved a recently fired employee at a large retail organization. The irked employee made his way from a store wireless network into the company’s core credit card processing systems. The purpose of the attack was to malign the company’s image by releasing the stolen data on the Internet. We will discuss the anatomy of the “hack”, the vulnerabilities exploited along the way, and our sleepless nights in Miami honing in on the attacker. He currently co-teaches a class at Carnegie Mellon University and has been invited to guest lecture at the University of Wisconsin. As an industry expert he has opined on security issues via columns for online publications like Securityfocus and SC magazine, and interviews with BBC UK Radio. Network Security, as well as Addison Wesley’s Extrusion Detection: Security Monitoring for Internal Intrusions.
Belani holds a Bachelor of Engineering in Computer Engineering from Bombay University and a Master of Science in Information Networking from Carnegie Mellon University. He currently leads the OWASP Java Project a world-wide consortium of Java security experts. Associates, a specialized services company which provides Computer Forensics, Electronic Evidence Discovery, Litigation Support and training to commercial and government clients. Jones is the Senior Partner responsible for the electronic evidence discovery and litigation support practices. Jones is an industry-recognized expert in computer security with over ten years experience in computer forensics and incident response.