There is additionally a distinction between the file format and compression algorithm used. For a decompression utility to correctly expand an archive of either the self-extracting or standard variety, it must be able to operate on both the file format and algorithm used. The exact executable code placed at the beginning of a self-extracting archive may therefore need to be varied depending on what options were used to create the archive.
Several programs can create self-extracting archives. There are also programs that create self-extracting archives on Unix as shell scripts which utilizes programs like tar and gzip which must be present in destination system. An early example of a self-extracting archive was the Unix shar archive in which one or more text files were combined into a shell script that when executed recreated the original files. Self-extracting archives can be used to archive any number of data as well as executable files.
They must be distinguished from executable compression, where the executable file contains a single executable only and running the file does not result in the uncompressed file being stored on disk, but in its code being executed in memory after decompression. Archiving files rather than sending them separately allows several related files to be combined into a single resource.
It also has the benefit of reducing the size of files not already efficiently compressed many compression algorithms cannot make already compressed data any smaller. Compression will therefore usually reduce the size of a plain text document but hardly affect a JPEG picture or a word processor document. This is because most modern Word Processor file formats now involve a certain level of compression already.
Self-extracting archives also extend the advantages of compressed archives to users who do not have the necessary programs installed on their computer to otherwise extract their contents, but are running a compatible operating system.
However, for users who do have archive managing software, a self-extracting archive may still be slightly more convenient. Self-extracting archives also allow for their contents to be encrypted for security, provided the chosen underlying compression algorithm and format allow for it.
In many cases though the file and directory names are not part of the encryption and can be seen by anyone, even without the key or password.
Additionally, some encryption algorithms rely on there being no known partial plaintexts available so if an attacker is able to guess part of the contents of the files from their names or context alone they may be able to break the encryption on the entire archive with only a reasonable amount of computing power and time. Care therefore needs to be taken or a more suitable encryption algorithm used.
A disadvantage of self-extracting archives is that running executables of unverified reliability, for example when sent as an email attachment or downloaded from the Internet, may be a security risk. An executable file described as a self-extracting archive may actually be a malicious program. One protection against this is to open it with an archive manager instead of executing it losing the minor advantage of self-extraction ; the archive manager will either report the file as not an archive or will show the underlying metadata of the executable file - a strong indication that the file is not actually a self-extracting archive.
Additionally, some systems for distributing files do not accept executable files in order to prevent the transmission of malicious programs. These systems disallow self-extracting archive files unless they are cumbersomely renamed by the sender to, say, somefiles.
This technique is gradually becoming less effective however as an increasing number of security suites and antivirus software packages instead scan file headers for the underlying format rather than relying on a correct file extension.
These security systems will not be fooled by an incorrect file extension and are particularly prevalent in the analysis of email attachments. By using this website, you consent to the use of cookies. For more detailed information regarding the use of cookies on this website, please see our "Privacy Policy". If you prefer not to have cookies stored within your web-browser, please adjust your browser settings accordingly.
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