Consider a folder containing the following files:

(file1.txt, file2.doc, file3.pdf) all zipped and password protected, if attacker had one of these file, can use it for decrypting all without knowing the password?

Note: I used very strong password which is 100 in length for example:



That would be a form of know plain-text attack. Zip uses AES these days to encrypt files and AES is not susceptible to these type of attacks.

Please refer to: Compute the AES-encryption key given the plaintext and its ciphertext?

  • I also found that here: If you have a file from the encrypted ZIP archive in your hands, the whole archive can be usually unlocked in minutes by applying the known-plaintext attack. Similar ARJ archives are unlocked instantly. Fast recovery available only in case of "classical" encryption, not AES. – Akam Mar 7 '13 at 10:43

In don't believe that that would work on modern versions of zip software (as @lucasKauffman says), however there is a known plaintext attack for older version of zip crypto (more details here ), so if the archive uses that then it would enable the other files to be extracted potentially.

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