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Cryptographic hash functions must have several properties: Resistance to preimages: given x, it should be infeasible to find m such that h(m) = x. Resistance to second-preimages: given m, it should be infeasible to find m' such that h(m) = h(m'). Resistance to collisions: it should be infeasible to find m and m' such that m ≠ m' and h(m) = h(m'). These ...


3

The assessment of any strong 256 bit cryptographic hash as having a security level of either 128 or 256 bit depends entirely on how it is used. In an application where an attacker can succeed simply by finding any hash collision, the security level cannot exceed 128 bit since a simple birthday attack will (probabilitiscally) succeed after 2^128 random ...


3

No. In the context of a hash, "bits of security" is a measure of how many possible outputs a hash function has, and thus, how hard it is to find an input with a given output. It's on a logarithmic scale, so each additional bit doubles the security. You can't compare the security of SHA-256, AES-128, and ECC-256. They're totally different things: SHA-256 ...


1

Even a non-cryptographic hash can usually not be reversed (that is irrespective of other special properties of cryptographic hashes, such as collision/preimage resistance). The reason why it usually isn't possible is that you simply do not have enough information. A hash function (generally) turns N bits of input into M bits of output, where M is a small ...


8

The definition of a cryptographic hash function includes resistance to preimages: given h(x), it should be infeasible to recover x. A hash function being "reversible" is the exact opposite of that property. Therefore, you can have no more a "reversible hash function" than you can have a fish allergic to water. Possibly you might want a hash function ...



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