| | 24 | ''p'' is the success probability of an attack (0 < ''p'' <= 1). ''N'' is the number of targets for preimage attacks; this assumes that the attacker has stored the relevant hashes for ''N'' files and is content with finding a preimage for any of them. Note that since the attacker must also expend work to obtain each target hash, the cost of brute force cannot be reduced below a "square root" attack. For example, the work to forge an immutable file (attack !#3) by brute force cannot be reduced to less than sqrt(''p'').2^(''r''+''t'')/2^ (roughly the same work as a collision attack), no matter how many targets are available. |
