10.1007/11787006_15
Krzysztof Pietrzak
Krzysztof Z
Pietrzak
A tight bound for EMAC
LNCS
Springer
2006
2018-12-11T12:02:04Z
2019-05-10T12:19:51Z
conference
https://research-explorer.app.ist.ac.at/record/3216
https://research-explorer.app.ist.ac.at/record/3216.json
We prove a new upper bound on the advantage of any adversary for distinguishing the encrypted CBC-MAC (EMAC) based on random permutations from a random function. Our proof uses techniques recently introduced in [BPR05], which again were inspired by [DGH + 04].
The bound we prove is tight — in the sense that it matches the advantage of known attacks up to a constant factor — for a wide range of the parameters: let n denote the block-size, q the number of queries the adversary is allowed to make and ℓ an upper bound on the length (i.e. number of blocks) of the messages, then for ℓ ≤ 2 n/8 and q≥ł2 the advantage is in the order of q 2/2 n (and in particular independent of ℓ). This improves on the previous bound of q 2ℓΘ(1/ln ln ℓ)/2 n from [BPR05] and matches the trivial attack (which thus is basically optimal) where one simply asks random queries until a collision is found.