Re: How long to crack a five, six, and seven digit passphrase in WinZip, WinRar, 7-Zip?

Ertugrul Söylemez wrote:
[...]
In your example, N would be 62 (all alphanumerics). Then,

L = 5 => T = 458066416 / V
L = 6 => T = 28400117792 / V
L = 7 => T = 1760807303104 / V

and none of them being very secure. Modern systems can well test 10
million passphrases in a second, which makes even the L = 7 password
breakable in about 48 hours in average.

From what I recall WinZip does use key strengthning [1] to increase the time it takes to test one password, so I don't think you can really test 10 million passwords per second on a regular PC.

Also, you can use symbols and spaces in the password ("!"#$%&/()", etc.), so the alphabet is actually larger than 62.

I recommend at least L = 14 for real security.

Having said that, I also agree with this statement. If you're concerned about the data on the zip file, use 14 letters at least...

--
Paulo Marques

[1] http://en.wikipedia.org/wiki/Key_strengthening
.