
	Where results make sense

Topic: Hash function

Related Topics

Hash table

Cryptographic hash function

Hash

Pearson hashing

HMAC

MD5

SHA1

Cyclic redundancy check

Linear search

Checksum

Binary search

Algorithm

Big O notation

Luhn algorithm

List of data structures

In the News (Tue 10 Nov 09)

Northern Trust

Marvin Harrison

Peter Chernin

Gary Locke

Match Play

Penelope Cruz

Mickey Rourke

AR Rahman

Danny Boyle

Hugh Jackman

	Q94: What is a Hash Function?
		Hash functions with just this property have a variety of general computational uses, but when employed in cryptography the hash functions are usually chosen to have some additional properties.
		A hash function H is said to be one-way if it is hard to invert, where "hard to invert" means that given a hash value h, it is computationally infeasible to find some input x such that H(x) = h.
		Since hash functions are generally faster than digital signature algorithms, it is typical to compute the digital signature to some document by computing the signature on the document's hash value, which is small compared to the document itself.
	www.x5.net /faqs/crypto/q94.html (311 words)

	Hash function - Wikipedia, the free encyclopedia
		This property is a consequence of hash functions being deterministic.
		Functions intended for cryptographic hashing, such as MD5, are commonly used as stock hash functions.
		Hash functions that are truly random with uniform output (including most cryptographic hash functions) are good in that, on average, only one or two probes will be needed (depending on the load factor).
	en.wikipedia.org /wiki/Hash_function (1342 words)

	What is hashing? - a definition from Whatis.com - see also: hash, hash function (Site not responding. Last check: )
		Hashing is the transformation of a string of characters into a usually shorter fixed-length value or key that represents the original string.
		Hashing is used to index and retrieve items in a database because it is faster to find the item using the shorter hashed key than to find it using the original value.
		The digital signature is transformed with the hash function and then both the hashed value (known as a message-digest) and the signature are sent in separate transmissions to the receiver.
	whatis.techtarget.com /definition/0,289893,sid9_gci212230,00.html (805 words)

	Hash Functions - CryptoDox
		It is often also called a "message digest." Hash functions are used for digital signatures such as RSA and DSA, but also for the construction of MACs (message authentication codes), the protection of passwords, and for the derivation of independent secret keys from a single master key.
		Cryptographic hash functions are an essential building block for applications that require data integrity, such as detectors of computer viruses, Internet security (for example PGP or IPSEC), and the security of electronic commerce and banking.
		A hash function must be a one-way function, which means that finding an input corresponding to a given output string is difficult: Even an opponent who wants to spend a significant amount of money, say $10 million, will have a negligible success probability.
	www.cryptodox.com /index.php?title=Hash_Functions (247 words)

	.:: General Purpose Hash Function Algorithms - By Arash Partow ::.
		When algorithms which contain hash functions are analyzed it is generally assumed that hash functions have a complexity of O(1), that is why look-ups for data in a hash-table are said to be on average of O(1) complexity, where as look-ups of data in maps (Red-Black Trees) are said to be of O(logn) complexity.
		This is achieved through the use of multiple distinct hash functions and also by allowing the result of a query for the existance of a particular type to have a certain amount of error.
		It is a simple hash function using a strange set of possible seeds which all constitute a pattern of 31....31...31 etc, it seems to be very similar to the DJB hash function.
	www.partow.net /programming/hashfunctions (2479 words)

	A Hash Function for Hash Table Lookup
		Most of the two dozen old hashes I've replaced have had owners who wouldn't accept a new hash unless it was a plug-in replacement for their old hash, and was demonstrably better than the old hash.
		hash = (hash ^ (hash>>10) ^ (hash>>20)) & mask;
		Zobrist hashes are especially favored for chess, checkers, othello, and other situations where you have the hash for one state and you want to compute the hash for a closely related state.
	burtleburtle.net /bob/hash/doobs.html (3913 words)

	AspEncrypt.com - Crypto 101: One-way Hash Function
		A one-way hash function, also known as a message digest, fingerprint or compression function, is a mathematical function which takes a variable-length input string and converts it into a fixed-length binary sequence.
		Furthermore, a one-way hash function is designed in such a way that it is hard to reverse the process, that is, to find a string that hashes to a given value (hence the name one-way.) A good hash function also makes it hard to find two strings that would produce the same hash value.
		Although a one-way hash function is used mostly for generating digital signatures, it can have other practical applications as well, such as storing passwords in a user database securely or creating a file identification system.
	www.aspencrypt.com /crypto101_hash.html (307 words)

	Hash tables and hash functions
		The implementer of a hash table must provide some mechanism for resolving collisions, that is, for finding an alternative storage location for an element that cannot be stored in a previously occupied position proposed by the hash function.
		When the keys are integers and their range is many times larger than the range of hash table indices, the best and most commonly used hash function divides each key by the size of the hash table and returns the remainder (adding 1 if the array subscripts start at 1 rather than at 0).
		The hash function is applied to the key to determine which of these lists the new element should be added to; in the event of a collision, one simply puts all of the elements that hash to the same array subscript into the same list (often, in this context, called a bucket).
	www.math.grin.edu /~stone/courses/fundamentals/hash-tables.html (2438 words)

	Integer Hash Function
		Certainly the integer hash function is the most basic form of the hash function.
		One such use for this kind of hash function is to hash a 64 bit virtual address to a hash table index.
		The integer hash function can be used to post condition the output of a marginal quality hash function before the final address calculation is done.
	www.concentric.net /~Ttwang/tech/inthash.htm (1821 words)

	hash function
		Bob Jenkins' fast, parameterizable, broadly applicable hash function (C) including code for and evaluations of many other hash functions.
		Arash Partow's implementations of various General Hash Functions (C, C++, Pascal, Object Pascal, Java, Ruby, Python) and Bloom filter for strings.
		Hash functions for strings (C) and (C and Perl).
	www.nist.gov /dads/HTML/hash.html (265 words)

	ONJava.com -- Optimizing Hash Functions For a Perfect Map
		A hash function cannot generally guarantee every data item maps to a different index, so the structure of a hash table is complicated by needing to maintain a list at every index, allowing multiple objects to be held at any index.
		implementations with perfect hash functions are much simpler than using generic hash functions; they consist of two arrays, one for the keys and one to hold all corresponding values.
		A hash function which maps each key to a unique index and leaves no empty entries in the table is called a minimal perfect hash function).
	www.onjava.com /pub/a/onjava/2001/01/25/hash_functions.html (958 words)

	RSA Laboratories - 2.1.6 What is a hash function?
		A hash function H is a transformation that takes an input m and returns a fixed-size string, which is called the hash value h (that is, h = H(m)).
		Since hash functions are generally faster than encryption or digital signature algorithms, it is typical to compute the digital signature or integrity check to some document by applying cryptographic processing to the document's hash value, which is small compared to the document itself.
		Given a compression function, a hash function can be defined by repeated applications of the compression function until the entire message has been processed.
	www.rsa.com /rsalabs/node.asp?id=2176 (525 words)

	Cryptographic hash function - Wikipedia, the free encyclopedia
		In cryptography, a cryptographic hash function is a hash function with certain additional security properties to make it suitable for use as a primitive in various information security applications, such as authentication and message integrity.
		An ideal hash function would be maximally "boring": it would have no interesting properties such as length extension, and the only interesting way it would differ from a random function would be in that it was deterministic and efficiently computable.
		The SHA hash functions are a series of functions developed by the NSA: SHA, also known as SHA-0, SHA-1 and four flavours of a function known as SHA-2.
	en.wikipedia.org /wiki/Cryptographic_hash_function (1630 words)

	Hash Functions and Block Ciphers
		A hash function for hash table lookup should be fast, and it should cause as few collisions as possible.
		If you know the keys you will be hashing before you choose the hash function, it is possible to get zero collisions -- this is called perfect hashing.
		A block cipher is a reversible function g:KxB->C, which maps a key in K and a block in B into a block in C. Usually B and C are the same set, so the block cipher permutes B in a key-specific way.
	burtleburtle.net /bob/hash (1349 words)

	The Hash Table Library
		Hash tables, sometimes also known as associative arrays, or scatter tables, are a data structure that offers fast lookup, insertion, and deletion of (key, value) pairs.
		Hashing was discovered and first published and implemented on computers in the early 1950s, and is based on a simple idea: transform the key to a number (the hash process), and then use that number to index a table.
		Return the maximum size of the hash table; this is the value used in the final modulo operation in the hash function.
	www.math.utah.edu /~beebe/software/hash/hash.html (2765 words)

	CITI: Projects: Linux scalability: Linux kernel hash behavior
		Hash table lookup operations are often O(n/m) (where n is the number of objects in the table and m is the number of buckets), which is close to O(1), especially when the hash function has spread the hashed objects evenly through the hash table, and there are more hash buckets than objects to be stored.
		The inode cache hash function is a shift-add function similar to the dentry cache hash function.
		Hashing on block numbers, as the Linux buffer cache does, turns out to require a particularly good hash function, as disk block numbers exhibit a great deal of regularity.
	www.citi.umich.edu /projects/linux-scalability/reports/hash.html (5872 words)

	NSPR Reference: Hash Tables (Chapter 33)
		The number of buckets in a hash table may be changed by the library functions during the lifetime of the table to optimize speed and space.
		A hash function maps a key to a hash number, which is then used to compute the index of the bucket.
		A pair of functions is used to allocate and tree the table, and another pair of functions is used to allocate and free the table entries.
	www.mozilla.org /projects/nspr/reference/html/plhash.html (1206 words)

	Hash Function
		A Hash Function is a Unary Function that is used by Hashed Associative Containers: it maps its argument to a result of type
		It is important for a Hash Function to minimize collisions where a collision is defined as two different arguments that hash to the same value.
		This is why Hashed Associative Containers are parameterized by the hash function: no one hash function is best for all applications.
	www.oopweb.com /CPP/Documents/STLGuide/Volume/HashFunction.html (288 words)

	Hash functions.
		MSVC seems to have a hard time optimizing the two faster hash functions, and surprisingly the open source gcc is able to turn in the outright fastest result.
		For the hash function to have the correct properties, it is assumed that CHAR_BIT is 8 and computations use 2s complement arithmetic.
		This is straightforward enough to do, by accepting the "hash" value as a parameter, and initializing it with some non-zero constant (since the point is to assume that the length is not available until all the data is read).
	www.azillionmonkeys.com /qed/hash.html (2215 words)

	Prime Double Hash Table
		Hash table should not be extremely vulnerable to poor hash function choices.
		A defense against hash function of unknown quality is to use hash table whose size is a prime number.
		Hash table traversal is the capability to retrieve key-value pair entries in the hash table sequentially.
	www.concentric.net /~Ttwang/tech/primehash.htm (1051 words)

	CIS Department > Tutorials > Software Design Using C++ > Hash Tables
		If that location is also in use, the rehash function can be applied again to generate a third location, etc. The rehash function has to be such that when we use it in the lookup process we again generate the same sequence of locations.
		A rehash function that skipped some numbers might cause you to not be able to insert an item because the empty locations are at indices that the rehash function cannot produce.
		A good rehash function should also try to avoid clustering as much as possible, whether clustering that occurs when items hash to the same location, or when items that hash to different locations compete for the same locations in their rehash paths.
	cis.stvincent.edu /html/tutorials/swd/hash/hash.html (4075 words)

	SparkNotes: Hash Tables: What is a Hash Table?
		A hash table is made up of two parts: an array (the actual table where the data to be searched is stored) and a mapping function, known as a hash function.
		The hash function is a mapping from the input space to the integer space that defines the indices of the array.
		In other words, the hash function provides a way for assigning numbers to the input data such that the data can then be stored at the array index corresponding to the assigned number.
	www.sparknotes.com /cs/searching/hashtables/section1.html (824 words)

	FNV hash (Site not responding. Last check: )
		All that is needed is to use a larger FNV-1 hash and to move the mask outside of the expression on the final statement.
		To produce a hash range between 0 and X use a n-bit FNV hash where n is smallest FNV hash that will produce values larger than X without the need for xor-folding.
		To ensure that the FNV hash values are the same on both Big Endian and Little Endian CPUs, we recommend that objects you always hash object such as integers from low to high byte significance order.
	www.isthe.com /chongo/tech/comp/fnv (4076 words)

	Dr. Dobb's \| Algorithm Alley \| September 1, 1997
		Bob knows the answer, and he has used his knowledge to design a new hash function that may be better than what you're using now.
		If keys are distributed uniformly, an excellent hash would be to choose the first few bytes of the key and use that as the hash value.
		The mixing function ought to be a permutation.
	www.ddj.com /184410284 (2379 words)

	PHP: hash - Manual
		Note that some of the hash algorithms provided are considered weak (e.g., md5, sha1 and haval128,3).
		With a string length of 1kB the difference is 10% advantage for hash() and shrinks further down to 3% with 10kB strings.
		If the hash functions are not available to you at the moment, and you want to future proof your code, then the code below will emulate two of the important hashing functions, they will also be automatically replaced with the faster versions if available.
	www.php.net /manual/en/function.hash.php (319 words)

	Hash function in C - Dev Shed
		Hash function in C C programming forum discussing all C derivatives, including C#, C++, Object-C, and even plain old vanilla C. These languages are low level languages, and used on projects such as device drivers, compilers, and even whole computer operating systems.
		The input is a pointer to a string to be hashed */
		Rational Functional Tester is an advanced, automated functional and regression testing tool for testers and GUI developers who need superior control for testing applications based on Java, Microsoft Visual Studio.NET, and Web technologies.
	forums.devshed.com /c-programming-42/hash-function-in-c-54284.html (1448 words)

Try your search on: Qwika (all wikis)