Cryptographic hash function

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Pigeon
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Cryptographic hash function

Post by Pigeon » Wed Mar 21, 2012 5:35 am

A cryptographic hash function is a hash function that can be defined as a deterministic procedure that takes an arbitrary block of data and returns a fixed-size bit string, the (cryptographic) hash value, such that an accidental or intentional change to the data will change the hash value. The data to be encoded is often called the "message," and the hash value is sometimes called the message digest or simply digest.

The ideal cryptographic hash function has four main or significant properties:

* it is easy to compute the hash value for any given message
* it is infeasible to generate a message that has a given hash
* it is infeasible to modify a message without changing the hash
* it is infeasible to find two different messages with the same hash

Cryptographic hash functions have many information security applications, notably in digital signatures, message authentication codes (MACs), and other forms of authentication. They can also be used as ordinary hash functions, to index data in hash tables, for fingerprinting, to detect duplicate data or uniquely identify files, and as checksums to detect accidental data corruption. Indeed, in information security contexts, cryptographic hash values are sometimes called (digital) fingerprints, checksums, or just hash values, even though all these terms stand for functions with rather different properties and purposes.

Verifying the integrity of files or messages

An important application of secure hashes is verification of message integrity. Determining whether any changes have been made to a message (or a file), for example, can be accomplished by comparing message digests calculated before, and after, transmission (or any other event).

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.

A related application is password verification. Passwords are usually not stored in cleartext, to improve security, but instead in digest form. To authenticate a user, the password presented by the user is hashed and compared with the stored hash. This also means that the original passwords cannot be retrieved if forgotten or lost, and they'll have to be replaced with new ones.


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Royal
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Re: Cryptographic hash function

Post by Royal » Wed Mar 21, 2012 3:49 pm

To be used in the alien interface parser?

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Pigeon
Posts: 18055
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Re: Cryptographic hash function

Post by Pigeon » Wed Mar 21, 2012 4:13 pm

...says the cryto parser

and yes

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