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marmoser

Member

From: Vienna, Austria

Registered: 2015-12-02

Posts: 13

Website

Trying to recover the zip password of an encrypted plaintext file

Hello Community!

I recently rediscovered my 15 year old journal, which I stored in an encrypted zip file. Of course I can't remember the password anymore. I've tried several applications to recover the password, but with no success.

-The encrypted file is entirely utf8 plaintext.
-I might be able to reconstruct certain phrases contained in the file, but not their exact location
-The archive does not include another file
-The unencrypted file is about 30kb
-The password should be quite long ( > 20 characters, at least I remember that  )

Is it theoretically possible to recover the password with the information given above or should I give up?

olive

Member

From: Belgium

Registered: 2008-06-22

Posts: 1,490

Re: Trying to recover the zip password of an encrypted plaintext file

It depends on the length of the encryption key. Due to (now abolished) US law, old softwares use no more than 40 bits encryption keys which might be recoverable (although stronger encryption has always been available on non-US servers). There a lot of tools available here and there on the web. If you used a stronger encryption key, I think you should give up. What's the point of using encryption if you expected it to be cracked easily?

Last edited by olive (2016-11-15 09:44:46)

marmoser

Member

From: Vienna, Austria

Registered: 2015-12-02

Posts: 13

Website

Re: Trying to recover the zip password of an encrypted plaintext file

Thanks for the reply! Encryption was done by a zip-plugin of a Norton Commander clone for Windows, which allowed to access zip files like a virtual file system. Since this app has never been open source, I can't look through the code. Is there a way to determine the length of the encryption keys?

marmoser

Member

From: Vienna, Austria

Registered: 2015-12-02

Posts: 13

Website

Re: Trying to recover the zip password of an encrypted plaintext file

Method = ZipCrypto Deflate
Host OS = FAT
Version = 20

'7z -l slt file.zip' provided this information.
So its not AES256, good! What should I do next? Where could I start?

frostschutz

Member

Registered: 2013-11-15

Posts: 1,418

Re: Trying to recover the zip password of an encrypted plaintext file

fcrackzip?