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Benjamin Walker
Benjamin Walker

( )( ) - .zip 3

If trailing or unmatched values are important to you, then you can use itertools.zip_longest() instead of zip(). With this function, the missing values will be replaced with whatever you pass to the fillvalue argument (defaults to None). The iteration will continue until the longest iterable is exhausted:

( )( ) - .zip 3


Here, you use itertools.zip_longest() to yield five tuples with elements from letters, numbers, and longest. The iteration only stops when longest is exhausted. The missing elements from numbers and letters are filled with a question mark ?, which is what you specified with fillvalue.

Files are compressed using the DEFLATE compression, as described in the "Appnote.txt" file. However, files are stored without compression if they are already compressed. zip/2 and zip/3 check the file extension to determine if the file is to be stored without compression. Files with the following extensions are not compressed: .Z, .zip, .zoo, .arc, .lzh, .arj.

$ zipinfo archive.zipArchive: 1743 bytes 5 files-rw-r--r-- 2.1 unx 4068 bX defN 11-May-13 14:25 magicsample.conf-rw-r--r-- 2.1 unx 204 bX defN 16-May-13 09:38 magicfile-rw-r--r-- 2.1 unx 132 bX defN 21-May-13 12:44 testingsomething.txt5 files, 4486 bytes uncompressed, 991 bytes compressed: 77.9%

$ unzip -l archive.zipArchive: Length Date Time Name -------- ---- ---- ---- 4068 05-11-13 14:25 magicsample.conf 204 05-16-13 09:38 magicfile 132 05-21-13 12:44 testingsomething.txt -------- ------- 4486 5 files

So you need to first concatenate the pieces, then repair the result. cat* concatenates all the files called* where the wildcard * stands for any sequence of characters; the files are enumerated in lexicographic order, which is the same as numerical order thanks to the leadings zeroes. > directs the output into the file

For a multipart zip coming from a Google Drive download I tried several of the explained methods but didn't work (well). I could finally do it in a simple way from the terminal:unzip finished extracting the same with the next part:unzip so on ...

If you compressed a single file, the zip archive takes the same name and adds a zip extension. If you compressed more than one file or folder, the zip archive will be named "" by default.

Compression bombs that use the zip formatmust cope with the fact that DEFLATE,the compression algorithm most commonly supported by zip parsers,cannot achieve a compression ratio greater than 1032.For this reason, zip bombs typically rely on recursive decompression,nesting zip files within zip files to get an extra factor of 1032 with each layer.But the trick only works on implementations thatunzip recursively, and most do not.The best-known zip bomb,,expands to a formidable 4.5 PBif all six of its layers are recursively unzipped,but a trifling 0.6 MB at the top layer.Zip quines,like those of Ellingsenand Cox,which contain a copy of themselvesand thus expand infinitely if recursively unzipped,are likewise perfectly safe to unzip once.

The giant-steps feature only pays when you are not constrained by maximum output file size.In, we actually want to slow file growth as much as possibleso that the smallest file, containing the kernel, can be as large as possible.Using giant steps in actually decreases the compression ratio.

Given that the N filenames in the zip fileare generally not all of the same length,which way should we order them,shortest to longest or longest to shortest?A little reflection shows that it is better toput the longest names last, because those names are the most quoted.Ordering filenames longest lastadds over 900 MB of outputto,compared to ordering them longest first.It is a minor optimization, though,as those 900 MBcomprise only 0.0003%of the total output size.

Suppose we want a zip bomb that expands to4.5 PB,the same size that recursively expands to.How big must the zip file be?Using binary search, we find that the smallestzip file whose unzipped size exceeds the unzipped size of 42.ziphas a zipped size of46 MB.

A version of this articleappeared at theUSENIX WOOT 2019workshop.The workshop talkvideo, slides, and transcriptare available.The source code of the paper is available.The artifactsprepared for submission are renamed to zblg.odt or zblg.docxwill cause LibreOffice tocreate and delete a number of 4 GB temporary filesas it attempts to determine the file format.It does eventually finish, and it deletesthe temporary files as it goes,so it's only a temporary DoS that doesn't fill up the disk.Caolán McNamara replied to my bug report.

Tavis Ormandy points outthat there are a number of "Timeout" results inthe VirusTotal for 2019-07-06).AhnLab-V3, ClamAV, DrWeb, Endgame, F-Secure, GData, K7AntiVirus, K7GW, MaxSecure, McAfee, McAfee-GW-Edition, Panda, Qihoo-360, Sophos ML, VBA32.The results for 2019-07-06)are similar, though with a different set of timed-out engines:Baido, Bkav, ClamAV, CMC, DrWeb, Endgame, ESET-NOD32, F-Secure, GData, Kingsoft, McAfee-GW-Edition, NANO-Antivirus, Acronis.Interestingly, there are no timeouts inthe results for;(screenshot 2019-07-06)perhaps this means that some antivirus doesn't support Zip64?

In ClamAV bug 12356,Hanno Böck reported that caused high CPU usagein clamscan.An initial patchto detect overlapping filesturned out to be incompletebecause it only checked adjacent pairs of files.(I personally mishandled this issueby posting details of a workaround on the bug tracker,instead of reporting it privately.)A later patchimposed a time limit on file analysis.


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