In cryptography, the preimage attack is a classification of attacks on cryptographic hash functions for finding a message that has a specific hash value. A cryptographic hash function should resist attacks on its preimage (message).
In the context of attack, there are two types of preimage resistance:
- preimage resistance: for essentially all pre-specified outputs, it is computationally infeasible to find any input which hashes to that output, i.e., to find any preimage x′ such that h(x′) = y when given any y for which a corresponding input is not known.
- second-preimage resistance: it is computationally infeasible to find any second input which has the same output as any specified input, i.e., given x, to find a 2nd-preimage x' != x such that h(x) = h(x′).
These can be compared with a collision resistance, in which it is computationally infeasible to find any two distinct inputs x, x′ which hash to the same output, i.e., such that h(x) = h(x′).
Collision resistance implies 2nd-preimage resistance of hash functions; and collision resistance does not guarantee preimage resistance.
Read more about Preimage Attack: Applied Preimage Attacks
Famous quotes containing the word attack:
“It is well worth the efforts of a lifetime to have attained knowledge which justifies an attack on the root of all evil—viz. the deadly atheism which asserts that because forms of evil have always existed in society, therefore they must always exist; and that the attainment of a high ideal is a hopeless chimera.”
—Elizabeth Blackwell (1821–1910)