Definitions
from Wiktionary, Creative Commons Attribution/ShareAlike License
 n. The set containing exactly every member of the domain of a function such that the member is mapped by the function onto an element of a given subset of the codomain of the function. Formally, of a subset B of the codomain Y under a function ƒ, the subset of the domain X defined by
Etymologies
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Examples

The functions are different from cryptographic hash functions, because they should be much faster and don't need to be resistant to preimage attack.

A preimage collision on MD5 (as requested in the article) is quite difficult.

Currently the strength of our standard digest algorithms (SHAx) against preimage attacks is roughly that of the output length, and against collision attacks it's something less than half the output length (this is a topic of active research on SHA1, which currently stands at
leaden commented on the word preimage
“. . . The subset . . . defined by . . .”? Well? (The suspense is killing me.)
Continues [obsessively refreshing the page]
November 9, 2011