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I am trying to recover a 7z file, but have forgotten the password. It's completely AES-256 encrypted (i.e. not even the filenames are available).

Steps:

  1. Generated hash file with 7z2hashcat.pl
  2. Ran a mask attack using hashcat -a 3 -m 11600 my.hash masks\rockyou-7-2592000.hcmask
  3. After ~55 hours, hashcat completed with status cracked
  4. The password identified in the hashcat.potfile is rejected by 7-zip

I found a discussion on hash collisions with old Office files here: https://security.stackexchange.com/a/211924

Is 7zip similarly vulnerable to hash collisions?

I would just try the steps in the linked post and see if I could generate more passwords, but given it could tie up my GPU for weeks, I'd appreciate any thoughts!

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  • And, the version of 7-Zip? – kelalaka Aug 26 '20 at 14:08
  • Unknown, the file was created in 2016, so not a recent version – Ben Owen Aug 26 '20 at 14:29
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    I suggest you try the hashcat forum at: hashcat.net/forum – user10216038 Aug 26 '20 at 17:23
  • Ironically, I didn't manage to sign up to the forum earlier because I couldn't answer the CAPTCHA! (the current stable version is 6.1.1, right?) – Ben Owen Aug 27 '20 at 18:41
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    (Thanks for the report! I forwarded this to the hashcat team, and they say that the CAPTCHA has been fixed) – Royce Williams Aug 30 '20 at 2:19

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