Bitcoin mining sha 256 hash generator

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This article needs additional citations for verification. This is the so-called avalanche effect. A cryptographic hash function is a special class of hash function that has certain properties which make it suitable for use in cryptography. Most cryptographic hash functions are designed to take a string of any length as input and produce a fixed-length hash value. A cryptographic hash function must be able to withstand all known types of cryptanalytic attack. This concept is related to that of a one-way function.

Functions that lack this property are vulnerable to preimage attacks. Functions that lack this property are vulnerable to second-preimage attacks. Such a pair is called a cryptographic hash collision. This property is sometimes referred to as strong collision resistance. Collision resistance implies second pre-image resistance, but does not imply pre-image resistance.

Informally, these properties mean that a malicious adversary cannot replace or modify the input data without changing its digest. Thus, if two strings have the same digest, one can be very confident that they are identical. Second pre-image resistance prevents an attacker from crafting a document with the same hash as a document the attacker cannot control. A function meeting these criteria may still have undesirable properties.

This property can be used to break naive authentication schemes based on hash functions. The HMAC construction works around these problems. In practice, collision resistance is insufficient for many practical uses. Checksum algorithms, such as CRC32 and other cyclic redundancy checks, are designed to meet much weaker requirements, and are generally unsuitable as cryptographic hash functions. In cryptographic practice, “difficult” generally means “almost certainly beyond the reach of any adversary who must be prevented from breaking the system for as long as the security of the system is deemed important”. The meaning of the term is therefore somewhat dependent on the application since the effort that a malicious agent may put into the task is usually proportional to his expected gain. For messages selected from a limited set of messages, for example passwords or other short messages, it can be feasible to invert a hash by trying all possible messages in the set.

In some theoretical analyses “difficult” has a specific mathematical meaning, such as “not solvable in asymptotic polynomial time”. An illustration of the potential use of a cryptographic hash is as follows: Alice poses a tough math problem to Bob and claims she has solved it. Bob would like to try it himself, but would yet like to be sure that Alice is not bluffing. An important application of secure hashes is verification of message integrity. For this reason, most digital signature algorithms only confirm the authenticity of a hashed digest of the message to be “signed”. Verifying the authenticity of a hashed digest of the message is considered proof that the message itself is authentic. MD5, SHA1, or SHA2 hashes are sometimes posted along with files on websites or forums to allow verification of integrity.

Storing all user passwords as cleartext can result in a massive security breach if the password file is compromised. One way to reduce this danger is to only store the hash digest of each password. In 2013 a Password Hashing Competition was announced to choose a new, standard algorithm for password hashing. The winner, selected in July 2015, was a new key stretching algorithm, Argon2. Verifiers SHALL store memorized secrets in a form that is resistant to offline attacks.

Memorized secrets SHALL be salted and hashed using a suitable one-way key derivation function. One of the main applications of a hash function is to allow the fast look-up of a data in a hash table. Being hash functions of a particular kind, cryptographic hash functions lend themselves well to this application too. However, compared with standard hash functions, cryptographic hash functions tend to be much more expensive computationally. Hash functions can also be used in the generation of pseudorandom bits, or to derive new keys or passwords from a single secure key or password.

There are several methods to use a block cipher to build a cryptographic hash function, specifically a one-way compression function. The methods resemble the block cipher modes of operation usually used for encryption. However, that approach can have costs in efficiency and security. A hash function must be able to process an arbitrary-length message into a fixed-length output. This can be achieved by breaking the input up into a series of equal-sized blocks, and operating on them in sequence using a one-way compression function. The compression function can either be specially designed for hashing or be built from a block cipher.