Andrew F writes: > So lets look at this from another view. How fast does a computer have to > be to fully bruit force a 64,128,256 key? ZettaFlops? YottaFlops? > http://en.wikipedia.org/wiki/Flops Lets assume a classical > computer. > > George, crankup that abacus of yours and let us know. I for one would be > very interested. > Or anyone else with big fat calculator? My is the wimpy drugstore kind...
As Gregory pointed out, "flops" is not the right measurement here because cryptographic operations are not floating-point operations. Checking a candidate key doesn't involve any floating-point math, but rather something like a block cipher decryption, which is a different sort of computation. The calculations to figure out brute-force speeds are really about simple multiplication and division. Just as the distance traveled by a moving object is given by distance = speed × elapsed time the number of decryptions attempted by a brute force search is given by decryptions = speed × elapsed time For example, if you have a 128-bit symmetric key, and you want to talk about a situation in which every possible key value has been checked, the relationship is 2¹²⁸ = speed × elapsed time or, if you prefer, 340282366920938463463374607431768211456 = speed × elapsed time If you want the time, just divide 2¹²⁸ by the speed. If you want the requisite speed to finish in a specified time, just divide 2¹²⁸ by that time. You just need to use consistent units, like measuring speed in trial decryptions per second and measuring elapsed time in seconds. In 1998 EFF built a brute-force cracking machine https://en.wikipedia.org/wiki/EFF_DES_cracker which "was capable of testing over 90 billion keys per second", against the DES system which used 56-bit keys. To find the time it would take that machine to be sure of testing every possible key, just divide 2⁵⁶ by 90 billion; the answer is given in seconds. (To convert seconds to days, divide by 86400.) -- Seth Schoen <[email protected]> Senior Staff Technologist https://www.eff.org/ Electronic Frontier Foundation https://www.eff.org/join 815 Eddy Street, San Francisco, CA 94109 +1 415 436 9333 x107 _______________________________________________ tor-talk mailing list [email protected] https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-talk
