Date: Thu, 04 Dec 2014 19:56:50 +0100 From: magnum <john.magnum@...hmail.com> To: john-users@...ts.openwall.com Subject: Re: Cracking multiple AES Zip files On 2014-12-04 17:08, Matt Weir wrote: > AES encrypted zip files have a high number of false positives in them. From > the Winzip spec: > > Password verification value > > This two-byte value is produced as part of the process that derives the > encryption and decryption keys from the password. When encrypting, a > verification value is derived from the encryption password and stored with > the encrypted file. Before decrypting, a verification value can be derived > from the decryption password and compared to the value stored with the > file, serving as a quick check that will detect *most*, but not all, > incorrect passwords. There is a 1 in 65,536 chance that an incorrect > password will yield a matching verification value; therefore, a matching > verification value cannot be absolutely relied on to indicate a correct > password. > > It also appears that the AES Zip verification value includes a salt. So my > question is, if I have multiple AES encrypted zip files that all use the > same password, would it be possible to have JtR see if a password matches > them all to reduce false positives? I'm not 100% sure we're talking about the same things here but Jim has fixed the zip "WinZIP" format in bleeding-jumbo (five months ago) so it no longer has false positives. I do not know the details other than it did not appear to involve actual unzipping. magnum
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