Sha1sum

sha1sum is a computer program which calculates and verifies SHA-1 hashes. It is commonly used to verify the integrity of files. It (or a variant) is installed by default in most Unix-like operating systems, including Mac OS X. Variants include shasum (which permits SHA1 through SHA512 hash functions to be selected manually) and sha224sum, sha256sum, sha384sum and sha512sum, which use a specific larger hash function than SHA-1. Versions for Microsoft Windows also exist.

Some cryptographical weaknesses have been found in SHA1.Fact|date=September 2008 However, sha1sum is still usable for general-purpose file checksumming, and is widely considered more secure than MD5 or a CRC.Fact|date=September 2008

Usage

To calculate the SHA1 hash of a file, simply give the filename as an argument to sha1sum.

$ sha1sum somefile da39a3ee5e6b4b0d3255bfef95601890afd80709 somefile

The output of sha1sum can be saved into a text file and used to verify the integrity of a file. If the output above is stored in the file somefile.sha1, the following command will compare the SHA1 hash of somefile with the hash stored in somefile.sha1.

$ sha1sum -c somefile.sha1 somefile: OK

The sha1sum command can also be used in an interactive mode to calculate the SHA1 hash of any arbitrary string of characters. After typing the sha1sum command without any arguments, type the string of characters in the terminal. End the string with an End-of-file character. The SHA1 hash will be displayed on the terminal next to the input string. For example:

$ sha1sum somestring CTRL+D CTRL+D

will result in the following output.

$ sha1sum somestringda63fb69aeb03c776bd23e91e2c1cb3df30135d3 -

See also

* GNU Core Utilities
* md5sum
* cksum

External links

* [http://www.linuxmanpages.com/man1/sha1sum.1.php The program's man page]
* [ftp://ftp.gnupg.org/gcrypt/binary/sha1sum.exe An implementation for Microsoft Windows]
* [http://www.mirrorservice.org/sites/ftp.gnupg.org/gcrypt/binary/sha1sum.exe Mirror for Windows version]
* [http://www.mirrorservice.org/sites/ftp.gnupg.org/gcrypt/binary/sha1sum.c Mirror for Windows version C sourcecode]
*The sha1sum program is part of the GNU Core Utilities package
* [http://www.slavasoft.com/fsum/ SlavaSoft FSUM - Fast File Integrity Checker]
* [http://jsummer.sourceforge.net/ JSummer] - a platform independent open source message digest tool for Unix/Linux and Windows with a GUI supporting sha1sum and other algorithms.