what is a checksum?

A checksum is a fixed-size datum computed from an arbitrary block of digital data for the purpose of detecting accidental errors that may have been introduced during its transmission or storage. The integrity of the data can be checked at any later time by recomputing the checksum and comparing it with the stored one. If the checksums do not match, the data was almost certainly altered (either intentionally or unintentionally).
Different functions can be used to compute a checksum. Examples include MD5 and SHA1.


Computing a Checksum under Windows

Checksum computing is not featured in windows as a standard functionality, but a several software tools exist for this.

For example, one can use the HashCheck Shell Extension (download).


Computing a Checksum under Linux

Under Linux, computing a checksum is very simple. The following commands can be used in the command line interface:

  • sha1sum filename
  • md5sum filename





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