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x - Faculty of Computer Science - Technische Universität Dresden

x - Faculty of Computer Science - Technische Universität Dresden

Remaining problems

Remaining problems of password based authentication based one way functions • Brute Force attack – function h() is public – value of h(x) is known to the attacker �try all possible values for x Considerations: • usually >> 1 Mio. h(x)/s on ordinary hardware • assumption: password uses only small letters • password length = 8 time needed: • first countermeasures: – limit false attempts • first password rules: 26 8 1 000 000 ∙ 60 ∙ 60 ≈ 58h – use a large alphabet (small and capitalised letters, numbers, specials) – use a long password Login Password … … dog h(bone) … … 81

Remaining problems of password based authentication based one way functions • first password rules: – use a large alphabet • (small, capitalised letters, numbers, specials) • time needed: – use a long password • remaining possible attacks: (26+ 26+10+ 30) 8 1 000 000 ∙ 60 ∙ 60 ∙ 24 ∙ 365.25 – increase in computation power • distributed approach • GPU • Moore’s law – pre-computation: • attacker creates lockup table • search time (example above): ld 26 + 26 + 10 + 30 8

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