Cryptographic hash function: Difference between revisions

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In practice, collision resistance is insufficient for many practical uses. In addition to collision resistance, it should be impossible for an adversary to find two messages with substantially similar digests; or to infer any useful information about the data, given only its digest. In particular, a hash function should behave as much as possible like a [[random function]] (often called a [[random oracle]] in proofs of security) while still being deterministic and efficiently computable. This rules out functions like the [[SWIFFT]] function, which can be rigorously proven to be collision-resistant assuming that certain problems on ideal lattices are computationally difficult, but, as a linear function, does not satisfy these additional properties.{{sfn|Lyubashevsky|Micciancio|Peikert|Rosen|2008| pp=54–72}}

Checksum algorithms, such as [[CRC32CRC-32]] and other [[cyclic redundancy check]]s, are designed to meet much weaker requirements and are generally unsuitable as cryptographic hash functions. For example, a CRC was used for message integrity in the [[Wired Equivalent Privacy|WEP]] encryption standard, but an attack was readily discovered, which exploited the linearity of the checksum.

=== Degree of difficulty ===

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* {{cite book | first1 = Christof | last1 = Paar | first2 = Jan | last2 = Pelzl | chapter-url = http://wiki.crypto.rub.de/Buch/movies.php | chapter = 11: Hash Functions | title = Understanding Cryptography, A Textbook for Students and Practitioners | publisher = [[Springer Science+Business Media|Springer]] | date = 2009 | url-status = dead | archive-url = https://archive.today/20121208212741/http://wiki.crypto.rub.de/Buch/movies.php | archive-date = 2012-12-08 }} (companion web site contains online cryptography course that covers hash functions)

* {{cite web | url = http://ehash.iaik.tugraz.at/wiki/The_eHash_Main_Page | title = The ECRYPT Hash Function Website }}

* [https://pwcreator.com/advanced-password-generator/ Advanced Encrypt Keys]

* [https://pwcreator.com/online-bcrypt-hash-generator-checker/ Bcrypt Hash Generator]

* {{cite web | url = http://www.guardtime.com/educational-series-on-hashes/ | title = Series of mini-lectures about cryptographic hash functions | first = A. | last = Buldas | date = 2011 | url-status = dead | archive-url = https://archive.today/20121206020054/http://www.guardtime.com/educational-series-on-hashes/ | archive-date = 2012-12-06 }}

* [https://github.com/CRPrinzler/HASH-verify Open source python based application with GUI used to verify downloads.]