# Puzzle friendliness

Canonical: https://web4.xpay.bi/en/wiki/wp-en-75952282/

Language: en

Published: 2026-10-24T22:58:56.646Z

Updated: 2026-10-24T22:58:56.646Z

In cryptography, puzzle friendliness is a property of some cryptographic hash functions. SHA-256 is a cryptographic hash function that is thought to have this property. Informally, a hash function is puzzle friendly if no solution exists which is better than just making random guesses, and the only way to find a solution is the brute force method. Although the property is very general, i

## Key facts

## Overview

In cryptography, puzzle friendliness is a property of some cryptographic hash functions. SHA-256 is a cryptographic hash function that is thought to have this property. Informally, a hash function is puzzle friendly if no solution exists which is better than just making random guesses, and the only way to find a solution is the brute force method. Although the property is very general, it is of particular importance to proof-of-work, such as in Bitcoin mining.

## Definition

A hash function H is said to be puzzle friendly if for every possible n-bit output value y, if k is chosen with a distribution with high min-entropy, then it is infeasible to find x such that H(k || x) = y (where the symbol "||" denotes concatenation) in time significantly less than 2n. In the above definition, the distribution has high min-entropy means that the distribution from which k is chosen is hugely distributed so that choosing some particular random  value from the distribution has only a negligible probability.

## Why this property is called puzzle friendliness

Let H be a cryptographic hash function and let an output y be given. Let it be required to find z such that H(z) = y. Let us also assume that a part of the string z, say k,  is known. Then, the problem of determining z boils down to finding x that should be concatenated with k to get z. The problem of determining x can be thought of a puzzle. It is really a puzzle only if the task of finding x is nontrivial and is nearly infeasible. Thus the puzzle friendliness property of a cryptographic hash function makes the problem of finding x closer to being a real puzzle.

## Application in cryptocurrency

The puzzle friendliness property of cryptographic hash functions is used in Bitcoin mining.

## See also

Collision resistance Collision attack Preimage attack

## Sources

- Puzzle friendliness · Wikipedia: https://en.wikipedia.org/?curid=75952282

Source: Wikipedia contributors — https://en.wikipedia.org/?curid=75952282&oldid=1369959732

Licence: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/

Adaptation notice: Reformatted for XPay; the source may be abridged, restructured or translated. Consult the cited revision for the original.