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 ===