42.zip Download

There are also zip files that, when uncompressed, yield identical copies of themselves.[5][6] A sophisticated form of zip bomb exploits the specifications of zip files and the Deflate compression algorithm to create bombs without the use of nested layers as used in 42.zip.[7]

Therefore, it is necessary to use nested zip files to achieve really outrageous compression ratios. If you have 2 layers of compression, the maximum ratio becomes 1032^2 = 1065024. For 3, it's 1099104768, and so on. For the 5 layers used in 42.zip, the theoretical maximum compression ratio is 1170572956434432. As you can see, the actual 42.zip is far from that level. Part of that is the overhead of the zip format, and part of it is that they just didn't care.

42.zip Download

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If I had to guess, I'd say that 42.zip was formed by just creating a large empty file, and repeatedly zipping and copying it. There is no attempt to push the limits of the format or maximize compression or anything - they just arbitrarily picked 16 copies per layer. The point was to create a large payload without much effort.

"Compression bombs that use the zip format must 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 that unzip recursively, and most do not. The best-known zip bomb, 42.zip, expands to a formidable 4.5 PB if all six of its layers are recursively unzipped, but a trifling 0.6 MB at the top layer. Zip quines, like those of Ellingsen and Cox, which contain a copy of themselves and thus expand infinitely if recursively unzipped, are likewise perfectly safe to unzip once."

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,42.zip,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.

Suppose we want a zip bomb that expands to4.5 PB,the same size that 42.zip 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.

No discussion on zip bombs is complete without the infamous 42.zip. It is a zip file consisting of 42 kilobytes of compressed data, containing five layers of nested zip files in sets of 16, each bottom layer archive containing a 4.3 gigabyte (4.3x109 bytes) file for a total of 4.5 petabytes (4.5x1015 bytes) of uncompressed data.

A zip bomb is a compressed ZIP archive file that halts or crashes the system which reads it. The decompression software, when uncompresses such an archive file, takes an enormous amount of disk space, processing time, or memory. This makes the executing system go out of resources and crash eventually. One such example of ZIP Bomb files is 42.zip compressed archive whose size is 42 kilobytes but expands to 4.5 petabytes of uncompressed data.

42.zip is the best-known example zip archive file that has a size of just 42kb, but when expanded, it reaches to a size of 4.5 PB, which is well over the size of any available storage system. It consists of recursively nested zip-files, where the lowest level zip file decompresses to a sie of 4.3 GB. The construction uses the most common DEFLATE compression algorithm which is compatible with most zip parsers. 006ab0faaa