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'''cksum''' is a [[command (computing)|command]] in [[Unix-like]] operating systems that generates a [[checksum]] value for a file or stream of data. The cksum command reads each file given in its arguments, or [[Standard streams|standard input]] if no arguments are provided, and outputs the file's [[cyclic redundancy check|CRC]] checksum and [[byte]] count.

The <tt>cksum</tt> command can be used to verify that files transferred by unreliable means arrived intact. However, the CRC checksum calculated by the cksum command is not [[Cryptographic hash function|cryptographically secure]]: While it guards against ''accidental'' corruption (it is unlikely that the corrupted data will have the same checksum as the intended data), it is not difficult for an attacker to ''deliberately'' corrupt the file in a specific way that its checksum is unchanged. Unix-like systems typically include other commands for cryptographically secure checksums, such as [[sha256sum]].

== Interoperability ==

The standard <tt>cksum</tt> command, as found on most UNIX-like operating systems (including GNU/Linux, *BSD, Mac OS X, and Solaris) uses a CRC algorithm based on the [[Frame check sequence|ethernet standard frame check]] and is therefore interoperable between implementations. This is in contrast to the [[Sum (Unix)|sum command]], which is not as interoperable. It is however not compatible with the CRC-32 calculation. On [[Tru64]] operating systems, the <tt>cksum</tt> command returns a different CRC value, unless the [[environment variable]] <code>CMD_ENV</code> is set to <code>xpg4</code>.

== Algorithm ==
cksum uses the [[generator polynomial]] 0x04C11DB7 and appends to the message its length in [[little endian]] representation. That length has [[null byte]]s trimmed on the right end.

== Syntax ==

<source lang="bash">
cksum [FILE]...
cksum [OPTION]
</source>

==Usage example==
<source lang="console">
$ cksum test.txt
4038471504 75 test.txt
</source>

where <code>4038471504</code> represents the checksum value and <code>75</code> represents the file size of <code>test.txt</code>.

== See also ==
* [[Cyclic redundancy check]]

==Source==
[http://wikipedia.org/ http://wikipedia.org/]

[[Category:Cryptography]]
[[Category:Checksum algorithms]]

Cksum - Revision history

Admin: Created page with "'''cksum''' is a command in Unix-like operating systems that generates a checksum value for a file or stream of data. The cksum command reads e..."