●●●●● ●●●● ●●0 Brute-Force Attack ●●● ●●●● o Attacker tries every possible key on a piece of ciphertext until an intelligible translation into plaintext is obtained proportional to key size assume either know /recognise plaintext Number of Alternative Time required at 10 Key Size(bits) Key Time required at I encryption/ps encryptions 32 232=43x10 21s=358mus 2. 15 milliseconds 20=72x10 As=ll42 years 10.01 hours 212=34x103 21271s=54x102yeas 5. x 10 years 2168=37x1030 s=59×10yean 59 x 100yean 26 characters 26=4×102x1°15s=64x10yean 6.4 x I( years (permutation)COMP4690, HKBU 8 Brute-Force Attack ⚫ Attacker tries every possible key on a piece of ciphertext until an intelligible translation into plaintext is obtained. ⚫ proportional to key size ⚫ assume either know / recognise plaintext