Hello world for the RAR virtual machine (RarVM)
Believe it or not, rar archives can contain simple, similar to x86, bytecode for the RarVM virtual machine. This was done in order to be able to introduce filters (preprocessors) into the archive for two-way conversion of input data in order to increase redundancy and increase the degree of compression.
For example, there is a filter "Intel E8 preprocessing", the beginnings of which probably come with LZX, which is designed to increase redundancy in the x86 code.
WinRAR includes many standard filters to increase the compression ratio for typical input data, but also allows you to include them directly in the archives!
Tavis Ormandy - the person who found out about it, did not find any tools for working with filters in RAR archives, and therefore wrote his own.
Read more on the Tavis Ormandy page.
For example, there is a filter "Intel E8 preprocessing", the beginnings of which probably come with LZX, which is designed to increase redundancy in the x86 code.
WinRAR includes many standard filters to increase the compression ratio for typical input data, but also allows you to include them directly in the archives!
Tavis Ormandy - the person who found out about it, did not find any tools for working with filters in RAR archives, and therefore wrote his own.
Read more on the Tavis Ormandy page.
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Source: https://habr.com/ru/post/152803/
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