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Can a hash function have no collisions?

Can a hash function have no collisions?

Ideally, a hash function returns practically no collisions – that is to say, no two different inputs generate the same hash value. This is particularly import for cryptographic hash functions: hash collisions are considered a vulnerability.

How do you know if a hash function is good?

Characteristics of a Good Hash Function. There are four main characteristics of a good hash function: 1) The hash value is fully determined by the data being hashed. 2) The hash function uses all the input data. 3) The hash function “uniformly” distributes the data across the entire set of possible hash values.

Which of the following hash functions never result in collision?

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In computer science, a perfect hash function h for a set S is a hash function that maps distinct elements in S to a set of m integers, with no collisions. In mathematical terms, it is an injective function. Perfect hash functions may be used to implement a lookup table with constant worst-case access time.

Is a hash value unique?

Any ‘fixed output size’ hash is not unique by math, but rather by our ability to compute things. A sort of ‘pseudo-unique’, if you will, just like ‘pseudo-random’. And we only say hash functions produce unique outputs because we aren’t powerful enough to find two identical hashes of different strings.

Why do hash functions have collisions?

Because hash functions have infinite input length and a predefined output length, there is inevitably going to be the possibility of two different inputs that produce the same output hash. If two separate inputs produce the same hash output, it is called a collision.

Why does hash functions need to be collision resistant?

The pigeonhole principle means that any hash function with more inputs than outputs will necessarily have such collisions; the harder they are to find, the more cryptographically secure the hash function is. Cryptographic hash functions are usually designed to be collision resistant.

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What makes a bad hash function?

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. Similarly, if two keys are simply digited or character permutations of each other (such as 139 and 319), they should also hash into different values.

What characteristics are needed in secure hash function?

SHA Characteristics Cryptographic hash functions are utilized in order to keep data secured by providing three fundamental safety characteristics: pre-image resistance, second pre-image resistance, and collision resistance.

Why do hash functions need to be collision resistant?