Checksumming
From TWUUG
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About Checksums
The concept of a checksum (in the context of linux distributions) is in place to make sure that a file you downloaded (typically an ISO of a linux distribution, or something else) is a valid copy of what the original file is. Minor errors in file transfer that can corrupt files are very common over HTTP/FTP, especialy with very large files such as Linux ISO's.
The following are some highly utilized checksum methods:
- MD5
- SHA1
- ASC
MD5
The most common checksum is an MD5 checksum. The checksum is created by running the data through the MD5 message-digest algorithm. The algorithm outputs a 32 hexadecimal character output. This output is exceedingly hard to duplicate with a non-identical file, this is what makes the MD5 checksums so reliable.
These usually have the same filename as an ISO you downloaded with .md5 at the end, or for a group of files, they may come in a file called MD5SUMS.
It is very easy to use and many tools are freely available to check the validity of your download.
Linux/Unix Tools
- md5sum - An Opensource GPL-Licensed Command Line based MD% generator and checker.
Windows Tools
- md5summer - A Opensource GPL-licensed GUI based MD5summing application that you can use to create and verify checksums.
SHA1
With SHA1 files, the checksum is created by running the data through the SHA1 (US Secure Hash Algorithm 1) message-digest algorithm. The algorithm outputs a 40 hexadecimal character output.
Linux/Unix Tools
Windows Tools
None Entered Yet
ASC and SIG
ASC and SIG files are used for file encryption, author verification and checksums.
For more information go to Single file Encryption and Verification.
Checksumming Tools