- A good hash function should have the following properties: Efficiently computable. Should uniformly distribute the keys (Each table position equally likely for each key) For example: For phone numbers, a bad hash function is to take the first three digits. A better function is considered the last three digits
- cs50-section / code / 7 / sample-hash-functions / good-hash-function.c Go to file Go to file T; Go to line L; Copy path Neel Mehta Improve comment. Latest commit 67404df Oct 22, 2015 History. 0 contributors Users who have contributed to this file 26 lines (23 sloc) 694 Bytes Raw Blame /* * Most.
- // Initialize hash lookup so that it maps the characters // in your string to integers between 0 and 31 int hashLookup[256]; // Hash function for six character strings. int hash(const char *str) { int ret = 0, mult = 1; for (const char *p = str; *p; *p++, mult *= 32) { assert(*p >= 0 && *p < 256); ret += mult * hashLookup[*p]; } return ret;
- Hash Table is a data structure which stores data in an associative manner. In hash table, the data is stored in an array format where each data value has its own unique index value. Access of data becomes very fast, if we know the index of the desired data. Implementation in C

By using a Global Hash Function, one can query the address space to determine the node(s) that will be holding the data corresponding to the key and then subsequently query the node directly for the required data Good hash functions tries to use every bit of the input while keeping the calculation time minimal. If you only need some hash code, try to multiply the bytes with prime numbers, and sum them. Shar Let's call B the number of buckets, and H the hash code of the key. Adding an entry to a hash table looks like this (pseudo code): // Calculate the hash code of the key H = key.GetHashCode() // Calculate the index of the bucket where the entry should be added bucketIndex = H mod B // Add the entry to that bucket buckets[bucketIndex].Add(entry Answer: Hashtable is a widely used data structure to store values (i.e. keys) indexed with their hash code. Hash code is the result of the hash function and is used as the value of the index for storing a key. If two distinct keys hash to the same value the situation is called a collision and a good hash function minimizes collisions

A hash table is a randomized data structure that supports the INSERT, DELETE, and FIND operations in expected O(1) time. The core idea behind hash tables is to use a hash function that maps a large keyspace to a smaller domain of array indices, and then use constant-time array operations to store and retrieve the data.. 1. Dictionary data types. A hash table is typically used to implement a. With a good hash function, this kind of hash table requires an average of one operation per lookup, plus the time to hash the key (but often the keys are relatively short string) FNV-1 is rumoured to be a good hash function for strings. For long strings (longer than, say, about 200 characters), you can get good performance out of the MD4 hash function. As a cryptographic function, it was broken about 15 years ago, but for non cryptographic purposes, it is still very good, and surprisingly fast Let hash function is h, hash table contains 0 to n-1 slots. Now we want to insert an element k. Apply h (k). If it results x and the index x already contain a value then we again apply hash function that h (k, 1) this equals to (h (k) + 1) mod n. General form: h1 (k, j) = (h (k) + j) mod n. Example: Let hash table of size 5 which. A Hash Table in C/C++ (Associative array) is a data structure that maps keys to values. This uses a hash function to compute indexes for a key. Based on the Hash Table index, we can store the value at the appropriate location. If two different keys get the same index, we need to use other data structures (buckets) to account for these collisions

** The hash function is a function that uses the constant-time operation to store and retrieve the value from the hash table, which is applied on the keys as integers and this is used as the address for values in the hash table**. Types of a Hash Function In C. The types of hash functions are explained below: 1. Division method. In this method, the. Characteristics of good hashing function. The hash function should generate different hash values for the similar string. The hash function is easy to understand and simple to compute. The hash function should produce the keys which will get distributed, uniformly over an array

- I think the function ht_hash has some severe flaws. First, as did owensss notice, the variable hashval is not initialized. On most architectures it will have the value that was left in the stack by the last function that used that location, maybe this one
- Hash functions for strings It is common to want to use string-valued keys in hash tables What is a good hash function for strings? The basic approach is to use the characters in the string to compute an integer, and then take the integer mod the size of the tabl
- Jenkins hash function: 32 or 64 bits XOR/addition Bernstein's hash djb2: 32 or 64 bits shift/add or mult/add or shift/add/xor or mult/xor PJW hash / Elf Hash: 32 or 64 bits add,shift,xor MurmurHash: 32, 64, or 128 bits product/rotation Fast-Hash: 32, 64 bits xorshift operations SpookyHash 32, 64, or 128 bits see Jenkins hash function: CityHash: 32, 64, 128, or 256 bits FarmHas
- general hashing function with good distribution. the actual function is hash(i) = hash(i - 1) * 65599 + str[i];what is included below is the faster version used in gawk. [there is even a faster, duff-device version] the magic constant 65599 was picked out of thin air while experimenting wit

- Well, suppose at some moment c == 'Z', so this expression amounts to 'Z' - '0'. If we substitute ASCII codes for these characters, then we get 90 - 48, this is equal to 42 which is ASCII code for '*' character. So you have transformed 'Z' into '*'. Is this somehow supposed to improve the quality of your hash function? I'm in doubt
- imize duplication of output values (collisions). Hash functions rely on generating favorable probability distributions for their effectiveness, reducing access time to nearly constant
- If the hash table size M is small compared to the resulting summations, then this hash function should do a good job of distributing strings evenly among the hash table slots, because it gives equal weight to all characters in the string. This is an example of the folding approach to designing a hash function

Hash functions are extremely useful and appear in almost all information security applications. A hash function is a mathematical function that converts a numerical input value into another compressed numerical value. The input to the hash function is of arbitrary length but output is always of fixed length This video walks through how to develop a good hash function. The keys to remember are that you need to find a uniform distribution of the values to prevent. **Good** **Hash** **Functions**. A **good** **hash** **function** may not prevent the collisions completely however it can reduce the number of collisions. Here, we will look into different methods to find a **good** **hash** **function**. 1. Division Method. If k is a key and m is the size of the **hash** table, the **hash** **function** h() is calculated as: h(k) = k mod The values returned by a hash function are called hash values, hash codes, hash sums, or simply hashes. To achieve a good hashing mechanism, It is important to have a good hash function with the following basic requirements: Easy to compute: It should be easy to compute and must not become an algorithm in itself

Providing a good hash function on a class can significantly affect the performance of adding those objects to a hash table. In a hash table with keys that provide a good implementation of a hash function, searching for an element takes constant time (for example, an O(1) operation) * A cryptographic hash function (CHF) is a mathematical algorithm that maps data of arbitrary size (often called the message) to a bit array of a fixed size (the hash value, hash, or message digest)*. It is a one-way function, that is, a function which is practically infeasible to invert. Ideally, the only way to find a message that produces a given hash is to attempt a brute-force search.

Different hash functions are given below: Hash Functions. The following are some of the Hash Functions −. Division Method. This is the easiest method to create a hash function. The hash function can be described as −. h(k) = k mod n. Here, h(k) is the hash value obtained by dividing the key value k by size of hash table n using the remainder Choose a Hash Function. The first step is to choose a reasonably good hash function that has a low chance of collision. But, since this is for illustration, I will be doing the opposite! Reverse Psychology, eh? We will be working only with strings (or character arrays in C) in this article Developed by Troy D. Hanson, any C structure can be stored in a hash table using uthash. Just include #include uthash.h then add a UT_hash_handle to the structure and choose one or more fields in your structure to act as the key. Then use HASH_ADD_INT, HASH_FIND_INT and macros to store, retrieve or delete items from the hash table

Hash functions. If we have an array that can hold M key-value pairs, then we need a function that can transform any given key into an index into that array: an integer in the range [0, M-1]. We seek a hash function that is both easy to compute and uniformly distributes the keys. Typical example * Currently the hash function has no relation to the size of your table*. i.e, you may have a table of 1000, but this hash function will spit out values waaay above that. I would start by investigating how you can constrain the outputted hash value to the size of your tabl

Hash tables. So, if GetHashCode doesn't return an id and cannot be used to test equality, what is it good for? GetHashCode mostly exists for one purpose: to serve as a hash function when the object is used as a key in a hash table. OK, but what is a hash table * Using primes for hash tables is a good idea because it minimizes clustering in the hashed table*. Item (2) is nice because it is convenient for growing a hash table in the face of expanding data. Item (3) has, allegedly, been shown to yield especially good results in practice eofbit, failbit and badbit are member constants with implementation-defined values that can be combined (as if with the bitwise OR operator). goodbit is zero, indicating that none of the other bits is set. Parameters none Return Value true if none of the stream's state flags are set. false if any of the stream's state flags are set (badbit, eofbit or failbit) Unary function object class that defines the default hash function used by the standard library. The functional call returns a hash value of its argument: A hash value is a value that depends solely on its argument, returning always the same value for the same argument (for a given execution of a program) I'll spend the rest of it showing you four good ways to define a hash function for use in unordered_map under C++0x, and with Google's help, it may end up providing the missing manual for this particular problem. Method 1 - A simple function

** The hash function H( i, k, r ) yields the offset of the desired record within the group**. As new records are inserted, groups grow in size. When the size of a group increases, a new hash function H<sub>m</sub> must be found, and new storage in D must be found for the group Your getKey(char*) function should be called hash or getIndex. It's getting an index into an array, whereas the word key is usually reserved for an associative array (i.e. a Hash Map, whereas this is a Hash Table) A collision cannot be avoided in case of hashing even if we have a large table size. We can prevent a collision by choosing the good hash function and the implementation method. Though there are a lot of implementation techniques used for it like Linear probing, open hashing, etc

- A good hash function requires avalanching from all input bits to all the output bits. (Incidentally, Bob Jenkins overly chastizes CRCs for their lack of avalanching -- CRCs are not supposed to be truncated to fewer bits as other more general hash functions are; you are supposed to construct a custom CRC for each number of bits you require.
- More about that under part 2: hash! part 1: load. Calling the load function on a dictionary text file stores the words in the dictionary data structure into a hash table, which basically maps keys.
- The goal of a good hash function is to make it extremely difficult for attackers to find ways of generating inputs that hash to the same value. Computing a hash should not be way too efficient,.
- With a good hash function, it should be hard to distinguish between a truely random sequence and the hashes of some permutation of the domain. Hash function ought to be as chaotic as possible. A small change in the input should appear in the output as if it was a big change. This is called the hash function butterfly effect

In computing, a hash table (hash map) is a data structure that implements an associative array abstract data type, a structure that can map keys to values.A hash table uses a hash function to compute an index, also called a hash code, into an array of buckets or slots, from which the desired value can be found.During lookup, the key is hashed and the resulting hash indicates where the. • A hash function should be consistent with the equality testing function • If two keys are equal, the hash function should map them to the same table location • Otherwise, the fundamental hash table operations will not work correctly • A good choice of hash function can depend on the type of keys, th

A hash function in cryptography is one of the big players, Because the hashing has non-reversible nature, you can't retrieve the original data from the hashed value. Now, this is a good thing when your intention is to keep hackers from accessing your plaintext data The purpose of hashing is to achieve search, insert and delete complexity to O(1). Hash function is designed to distribute keys uniformly over the hash table. Load factor α in hash table can be defined as number of slots in hash table to number of keys to be inserted. For open addressing, load factor α is always less than one Salting hashes sounds like one of the steps of a hash browns recipe, but in cryptography, the expression refers to adding random data to the input of a hash function to guarantee a unique output, the hash, even when the inputs are the same.Consequently, the unique hash produced by adding the salt can protect us against different attack vectors, such as hash table attacks, while slowing down. ** Hash functions are used for data integrity and often in combination with digital signatures**. With a good hash function, even a 1-bit change in a message will produce a different hash (on average, half of the bits change). With digital signatures, a message is hashed and then the hash itself is signed

Hash tables are fast only when their hash function is fast. Hash operations are dependent on the hash function. Most hash functions are not fast (as in a single computation without a loop fast). The performance of hash is not as good as people think. In general, assuming a good hash function, is it similar in performance to other techniques MCQ - Hashing Function in Data Structure. 11. What is direct addressing? A. Distinct array position for every possible key B. Fewer array positions than keys C. Fewer keys than array positions D. None of the mentioned View Answe Good Hash Functions. A good hash function may not prevent the collisions completely however it can reduce the number of collisions. Here, we will look into different methods to find a good hash function. 1. Division Method. If k is a key and m is the size of the hash table, the hash function h() is calculated as: h(k) = k mod A hash function takes an input of any size (eg : your email password, the full text of the Illiad, or a blu-ray video of Inception) The output of a hash function is of fixed size ( say, a 64. Hash function with n bit output is referred to as an n-bit hash function. Popular hash functions generate values between 160 and 512 bits. Efficiency of Operation. Generally for any hash function h with input x, computation of h(x) is a fast operation. Computationally hash functions are much faster than a symmetric encryption

- g it has five, otherwise stop where it ends)
- If h is a good hash function, then our hope is that the lists will be small. One great property of hashing is that all the dictionary operations are incredibly easy to implement. To perform a lookup of a key x, simply compute the index i = h(x) and then walk down the lis
- Hash functions for hash table lookup. 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.Otherwise, the best you can do is to map an equal number of keys to each possible hash value and make.
- Fowler-Noll-Vo is a non-cryptographic hash function created by Glenn Fowler, Landon Curt Noll, and Kiem-Phong Vo.. The basis of the FNV hash algorithm was taken from an idea sent as reviewer comments to the IEEE POSIX P1003.2 committee by Glenn Fowler and Phong Vo in 1991. In a subsequent ballot round, Landon Curt Noll improved on their algorithm

- And then it turned into making sure that the hash functions were sufficiently random. FNV-1a algorithm. The FNV1 hash comes in variants that return 32, 64, 128, 256, 512 and 1024 bit hashes. The FNV-1a algorithm is: hash = FNV_offset_basis for each octetOfData to be hashed hash = hash xor octetOfData hash = hash * FNV_prime return hash
- imum number of collisions. If the probability that a key, k, occurs in our collection is P(k), then if there are m slots in our hash table, a uniform.
- Basic Operations. Following are the basic primary operations of a hash table. Search − Searches an element in a hash table.. Insert − inserts an element in a hash table.. delete − Deletes an element from a hash table.. DataItem. Define a data item having some data and key, based on which the search is to be conducted in a hash table
- In general, a hash function is a function from E to 0..size-1, where E is the set of all possible keys, and size is the number of entry points in the hash table. We want this function to be uniform: it should map the expected inputs as evenly as possible over its output range. Java's implementation of hash functions for strings is a good example

What are **Hash** **Functions** and How to choose a **good** **Hash** **Function**? 20, Aug 19. Rearrange characters in a string such that no two adjacent are same using hashing. 19, Jun 19. Polynomial Division using Linked List. 23, Nov 20. **Hash** **Function** for String data in **C**#. 04, Jan 19 A good password hashing function must be tunable, slow, and include a salt. hashlib.pbkdf2_hmac (hash_name, password, salt, iterations, dklen=None) ¶ The function provides PKCS#5 password-based key derivation function 2. It uses HMAC as pseudorandom function Tuning hash table performance is actually easier than optimizing other parts of your code: you just replace a bad hash function with a good one, and the program instantly becomes faster. You don't have to change other functions; you don't even have to write any new code, because other people wrote some good hash functions for you hash functions are used so that each possible key hashes to one bucket location in each hash table. Each bucket holds a list of items that hash to that bucket, as in the case of chained hashing. When a key is inserted, it is inserted into the table whose corresponding bucke

** You want a powerful hash table, all you need is a good hash function**. The hash function we used above, that is the sum of ASCII codes modulo array size was a bad one. In any case, we have permutations of the same letters in the set, we will end up with the same value for the sum and leading same key which leads to disastrous collisions Hash functions are one of the foundational pillars of the blockchain technology. In fact, hashing singlehandedly imparts one of the most important properties to the blockchain: immutability. -AMAZONPOLLY-ONLYWORDS-START- The In's and Out's of Cryptographic Hash Functions In this article, we will acquaint ourselves with some of the most commonly used cryptographic hash functions in.

A collision is when two words have the same hash generated. Safe algorithms have a good collision resistance. That's to say that you have low chances to get the same hash for different words. But MD5 has a low collision resistance. So if you know that abc and def have the same generated hash (just an example) Techopedia Explains Hash Function. Hashing is used with a database to enable items to be retrieved more quickly. Hashing can also be used in the encryption and decryption of digital signatures. The hash function transforms the digital signature, then both the hash value and signature are sent to the receiver SHA-family. Secure Hash Algorithm is a cryptographic hash function developed by the NSA. Their first algorithm, SHA-0 (released in 1993) has been compromised years ago. SHA-1 (1995) generates a 160-bit (20-byte) hash output. SHA-1 improved MD5 by just increasing the hash value to a 40 digits long hexadecimal number. The algorithm also became compromised in 2005 as there were discovered. This function sums the ASCII values of the letters in a string. If the hash table size \(M\) is small compared to the resulting summations, then this hash function should do a good job of distributing strings evenly among the hash table slots, because it gives equal weight to all characters in the string. This is an example of the folding method to designing a hash function There are many hash functions, especially for c. Which one you want mainly depends on whether you need cryptographic strength or not. The SHA [1] family [2] of hashes is the standard for crypographic strength hash functions. If speed is important,..

usage: cmph [-v] [-h] [-V] [-k nkeys] [-f hash_function] [-g [-c algorithm_dependent_value][-s seed] ] [-a algorithm] [-M memory_in_MB] [-b algorithm_dependent_value] [-t keys_per_bin] [-d tmp_dir] [-m file.mph] keysfile Minimum perfect hashing tool -h print this help message -c c value determines: * the number of vertices in the graph for the algorithms BMZ and CHM * the number of bits per. A good hashing algorithm would exhibit a property called the avalanche effect, where the resulting hash output would change significantly or entirely even when a single bit or byte of data within a file is changed. A hash function that does not do this is considered to have poor randomization, which would be easy to break by hackers Only cryptographic hash functions may be used to implement password hashing. Hash functions like SHA256, SHA512, RipeMD, and WHIRLPOOL are cryptographic hash functions. It is easy to think that all you have to do is run the password through a cryptographic hash function and your users' passwords will be secure. This is far from the truth SMHasher is a test suite designed to test the distribution, collision, and performance properties of non-cryptographic hash functions - it aims to be the DieHarder of hash testing, and does a pretty good job of finding flaws with a number of popular hashes

insertion operations. Brie y, Cuckoo Hashing maintains two hash tables T 1 and T 2 with two independent hash functions h 1 and h 2, respectively, and a key is stored in exactly one of two locations, with one possible location in each hash table Hashing Function: The Core of Hashing Algorithm Behind every successful man, there is a great woman. — Groucho Marx Behind every successful hash algorithm, there is a great hash function. - We just made that up. Let's put the jokes aside for a moment and concentrate on the crux of the matter In cryptography, SHA-1 (Secure Hash Algorithm 1) is a cryptographic hash function which takes an input and produces a 160-bit (20-byte) hash value known as a message digest - typically rendered as a hexadecimal number, 40 digits long. It was designed by the United States National Security Agency, and is a U.S. Federal Information Processing Standard A good hash function has few collisions - i.e., If x 6= y, H(x) 6= H(y) with high probability An easy and powerful hash function is a polynomial mod some prime p - Consider each letter as a number (ASCII value is ﬁne

But not all hash functions are made the same, meaning different hash functions have different abilities. In Bitcoin's blockchain hashes are much more significant and are much more complicated because it uses one-way hash functions like SHA-256 which are very difficult to break Alternatives Functions. To use other hash functions can be a solution, but what criteria is used to choose a good one? The answer is simple, use hash functions with a bigger domain of results. For example, MD5 generates a 128 bits value, so the space of possible resulting values is 2 128 in size Good hash functions include cryptographic hash functions (e.g., SHA2-256, BLAKE2) and other hash functions that tend to produce wildly dispersed hash codes for nearby inputs. Poor hash functions include linear PRNGs such as LCGs and the Xorshift family You also want to have your hash functions be fast--you don't want to lose all the time savings you're getting from the hash table because you're computing the hash function really slowly. It's a delicate balance. For one good hash function, check out this hash algorithm. Now you're ready to implement your first hash table! Give it a try

A uniform hash function produces clustering C near 1.0 with high probability. A clustering measure of C > 1 greater than one means that the performance of the hash table is slowed down by clustering by approximately a factor of C.For example, if m=n and all elements are hashed into one bucket, the clustering measure evaluates to n.If the hash function is perfect and every element lands in its. Double Hashing: In this method: we follow the idea of applying a second hash function on the key whenever a collision occurs. It can be done as follows: (hash1(key) + c * hash2(key)) % Table_Size , where c keeps incremented by 1 upon every collision to find the next free slot

The hdestroy_r() function performs the analogous task for a hash table described by *htab, which was previously created using hcreate_r(). The hsearch () function searches the hash table for an item with the same key as item (where the same is determined using strcmp(3) ), and if successful returns a pointer to it Hash Tables are one of the most widely used data structures in computing. Knowing how they work and why they are efficient is important even if you never dir.. SpookyHash: a 128-bit noncryptographic hash. SpookyHash is a public domain noncryptographic hash function producing well-distributed 128-bit hash values for byte arrays of any length. It can produce 64-bit and 32-bit hash values too, at the same speed, just use the bottom n bits SHA-256 is a member of the SHA-2 cryptographic hash functions designed by the NSA. SHA stands for Secure Hash Algorithm. Cryptographic hash functions are mathematical operations run on digital data; by comparing the computed hash (the output from execution of the algorithm) to a known and expected hash value, a person can determine the data's integrity Although it is a good idea to understand the issues involved in choosing a hash function, if you program in Java, you can simply use the hashCode method that is supplied for every Object (including Strings).The method returns an integer j, and you can just use j mod TABLE_SIZE as your hash function. Of course, if your keys are members of a class that you define, you will need to implement the.

Fortunately, with an appropriately chosen hash table size and a good hash function, this situation happens very rarely. Still, every hashing scheme must have a collision resolution mechanism. This mechanism is different in the two principal versions of hashing: open hashing (also called separate chaining ) and closed hashing (also called open addressing ) Draw a hash table with open addressing and a size of 9. Use the hash function k%9. Insert the keys: 5, 29, 20, 0, 27 and 18 into your table (in that order). Suppose you are building an open address hash table with double hashing. The hash table capacity is n, so that the valid hash table indexes range from 0 to n. Fill in the blanks

Two or more keys hash to the same slot!! For a given set of n keys If n ≤ N, collisions may or may not happen, depending on the hash function If n > N, collisions will definitely happen (i.e., there must be at least two keys that have the same hash value) Avoiding collisions completely is hard, even with a good hash function 11 1 This operation usually returns the same hash for a given key. A good hash function should be efficient to compute and uniformly distribute keys. Hash functions help to limit the range of the keys to the boundaries of the array, so we need a function that converts a large key into a smaller key. This is the job of the hash function I am trying to optimize my hash function, for a separate chaining hash table that I have created from scratch. My hash function is as follows: Menu DaniWeb. Log In Sign Up Read Contribute Your algorithm is a common variation of a good hash that uses 33 instead of 37. It should work well in the general case. 0 0. Share This function returns a positive integer between 0 and NBUCKETS, which can be used as an index into the key and the value arrays. For example, hash_function(Tudor) returns 31687 and hash_function(Dumitras) returns 48160. Implement the hash function in enee140_hashtable.c. In the same file, declare the storage of the hash table as follows

Hashing Function Methods (Hashing Methods) Division Hash Method The key K is divided by some number m and the remainder is used as the hash address of K. h(k)=k mod m This gives the indexes in the range 0 to m-1 so the hash table should be of size m This is an example of uniform hash function if value of m will be chosen carefully Introduction Let's start with the core features of my C++ hashing library: computes CRC32, MD5, SHA1 and SHA256 (most common member of the SHA2 functions), Keccak and its SHA3 sibling optional HMAC (keyed-hash message authentication code); no external dependencies, small code size can work chunk-wise (for example when reading streams block-by-block Or you can verify a file's integrity by checking its hash value. Every file has unique data contained within it, and when you apply a certain algorithm called a cryptographic hash function to it, a string value is returned which is only valid for that file in its current state FNV hash history. The basis of the FNV hash algorithm was taken from an idea sent as reviewer comments to the IEEE POSIX P1003.2 committee by Glenn Fowler and Phong Vo back in 1991. In a subsequent ballot round: Landon Curt Noll improved on their algorithm. Some people tried this hash and found that it worked rather well. In an EMail message to Landon, they named it the ``Fowler/Noll/Vo'' or. With hashing, this element is stored in the slot h(k). This means that we use a hash function h(k) to compute the slot using the key. The hash function h maps the universe U into slots in the table T[0, 1, 2, . . . m-1] h: U → {0, 1, 2, . . . , m-1} where the size of the hash table m is much less than the size of the universe U

Key derivation¶. Key derivation and key stretching algorithms are designed for secure password hashing. Naive algorithms such as sha1(password) are not resistant against brute-force attacks. A good password hashing function must be tunable, slow, and include a salt.. hashlib.pbkdf2_hmac (hash_name, password, salt, iterations, dklen=None) ¶ The function provides PKCS#5 password-based key. A hash function is used to map data to other data of fixed size. A perfect hash function is injective, so there are no collisions. Every input has one fixed output. A cryptographic hash function is used for verification. With a cryptographic hash function you should to not be able to compute the original input. A very common use case is. 4-byte integer hash, half avalanche. Full avalanche says that differences in any input bit can cause differences in any output bit. A weaker property is also good enough for integer hashes if you always use the high bits of a hash value: every input bit affects its own position and every higher position. I'll call this half avalanche