How to Calculate Checksum Procedures
Checksums are values calculated from data using a variety of algorithms. Ideally, a checksum is unique for a given set of data and can be compared against a known checksum in order to verify the integrity of transmitted data. Common checksum algorithms include MD5, SHA1, and SHA256. Checksum algorithms are implemented through software utilities, many of them freeware. For example, you can use the md5sum checksum utility for Linux and verify the integrity of the file vlc-data_1.1.3-1squeeze6_all.deb.
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Instructions
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Determine that there is published checksum data for the file you wish to check. The file vlc-data_1.1.3-1squeeze6_all.deb is available at http://packages.debian.org/squeeze/all/vlc-data/download. On the download page are MD5, SHA1, and SHA256 checksums for the file. The MD5 checksum is c3d87384619652e404a929f35c9c28a1.
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Download the file.
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Calculate the checksum of the downloaded file by invoking md5sum followed by the file name. If vlc-data_1.1.3-1squeeze6_all.deb was downloaded to the directory /var/cache/apt/archives, then type at the command line (the # sign is the prompt and not part of what you would type): # md5sum /var/cache/apt/archives/vlc-data_1.1.3-1squeeze6_all.deb
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Verify that the result given to you by the checksum utility is the same value as the published result. The output from the command in the previous step should be c3d87384619652e404a929f35c9c28a1. If it is not, then the file has been either corrupted in transmission or tampered with.
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Tips & Warnings
SHA256 is considered to be the strongest checksum algorithm currently in use.
An incorrect checksum could indicate that a file has been maliciously tampered with. Do not install such files. Instead, look for another download site where you can obtain the file.
References
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