An SFV file essentially provides a means to assure the individual downloading any binaries from the Usenet that what they've received is not corrupted in any way. These files operate by, to use an analogy, checking the fingerprint of the file as determined by an algorithm. This sounds very technical but, from the end-user's point of view, it is a generally simple task. Some newsgroup readers allow the entire operation to be done via the familiar drag-and-drop file handling so common to users of both Macintosh and PC computers.
The SFV file uses a method of verification known as a "checksum". The checksum figure is generated by running the program data through the CRC32 algorithm. When the user uploads the files to the newsgroup, they generate the SFV by running the various binaries through this algorithm. When the file is downloaded by the recipient, they repeat the process. If both hexadecimal numbers generated by the algorithm match, the file is verified as being undamaged, uncorrupted and as being the entire file as it was intended to be used.
Various newsreader programs have this functionality built into their system. Generally, one will download the SFV files as part of a compressed archive, open the archive and extract the text file. This SFV file will contain the entire list of files included as well as certain sections which will be ignored by the verification software. These lines which will be ignored will be denoted by a semicolon at the beginning of the line. Most often, these lines are comments added to the file to provide for readability. They may contain any information but will not at all affect the processing of the file for verification purposes.
The SFV file may, in some instances, contain pathnames from the original user's computer. As an example, an MP3 file named "Music.MP3" may appear on the file as "C:UsersMain UserMy DocumentsMusic.MP3 " To check the file, one must either remove the path information or drag and drop the file separately into the verification program's interface. Generally, these files will be free of path names but it does happen on occasion and the files should be checked. These files are simply text and can be opened in any text editor included with one's operating system.
An SFV file should not be opened in a word processing program. It is possible that these files could contain macros and running those macros may compromise the security of the machine. Most NBZ programs contain features that allow these files to be handled easily. Remember that any compressed file should be scanned for viruses before it is extracted and that any files within the archive should be scanned again to make certain that there are no malicious programs included in the archive. The SFV algorithm provides not security, but assurance of usability. For those who download large files, it can ensure that they are what was desired before they are burned to a disc or otherwise used.
Marion Marshall specializes in writing and advising people on Usenet technologies. By visiting his website
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