In this scenario, it is not important to consider the expected number of AES operations for brute-force search of the AES key ( $2^$ of CPU time to find a password, that is less than 2 hours of wall clock time with a single 8-core PC, minutes for a powerful adversary. some header of the encrypted file(s) is known, for a file encrypted with AES, where the key has been determined from a user-supplied password. The question considers a (partially) known plaintext attack, where e.g. Yes, in the question's situation, a password-recovery attacks is entirely reasonable. So is this method plausible? or is there something wrong with it, like maybe the actual address of the bytes in the zip is different from the address in the unzipped file. ![]() Hence a list of possible passwords to rearrange the sequence begin to be narrowed down as the cracking progresses. This is the key that the document is encrypted with. A PDF will do two things when a password is entered for an encrypted PDF - It will derive a symmetric key from the user password. For instance, a 3ds file always starts with a header containing the bytes "4D4D". 2 Answers Sorted by: 7 Generally the target hash you want to break in the case of a PDF is the user hash, which is derived from the users password. However, the condition for this type of cracking is that the zip file contains known file types which have a determined data format and places certain data in certain locations in the file. Then by comparing the scrambled bytes with the 'expected' unscrambled bytes, the password can easily be determined by computing an algorithm that converts those bytes because both the scrambled bytes and the unscrambled bytes are known. Say if a portion of the data in the file is known, for example a string at the end of a file, or a header containing an expected sequence of bytes in a known file type. But I can't help thinking there's got to be a faster way.īecause the AES encryption scrambles the data contained in a zip file, the password could be found by unscrambling that data correctly. ![]() I heard that the fastest method to crack an AES-128 encryption, or and AES-256 encryption is by brute force, which can take billions of years.
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