Guaranteed WinZip attack
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That's the most powerful attack available in ARCHPR. It works similarly to known-plaintext attack described above, but doesn't require you to have any files from the archive. However, the archive itself should have at least 5 encrypted (password-protected) files, and have to be created with WinZip or any other ZIP archiver based on Info-ZIP sources.
Please note that only WinZip versions 8.0 and below are vulnerable for this particular attack (because of using weak random number generator). In version 8.1, the hole has been fixed, and so for archives created with this version (as well as newer ones) you will not be able to use this attack at all.
Just select the archive file name, Guaranteed WinZip attack from Type of attack drop-down box, and press Run; no other options needed. If the archive has been created with some other archiver, or contains less than 5 files, ARCHPR will show an error message.
The attack consists of three stages: first two are for searching the encrypted keys (needed to decrypt the archive), and the last one searches for the actual password (up to 10 characters).
Usually, first stage takes just a few minutes (the program may show Estimated remaining time as a few hours, but actually, that's the theoretical maximum, and in most cases it is MUCH faster). Second one is from 10 to 30 minutes, and the last stage (where the password itself is being recovered) is 2-3 minutes only. For the second stage, the time estimation is also not very accurate (to make it better, it would be needed to perform a lot of additional operations, while ARCHPR does its best to recover keys/password as fast as possible).
That attacks works in most cases (as already noted, for WinZip files only), and even if the password is very long (so it could not be found during the 3rd stage), ARCHPR will be able to decrypt the whole archive, so you will not need to supply a password to extract files from it. However, in some very rare cases (the probability is 1/256, i.e. 0,4% only), WinZip may create ZIP archives this attack fails on. ARCHPR identifies such archives and prints a warning message into the log window; actually, this message does not mean that the ARCHPR will definitely fail, but if first stage will be completed but no encryption keys found – sorry, you're out of luck. Just try the other attacks.
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