查看“CheckSum”的源代码


== 校验和 ==

原文出处：[https://help.ubuntu.com/community/Checksum Ubuntu Documentation]

原文作者：Ubuntu Community

授权许可：
* [http://creativecommons.org/licenses/by-sa/2.0/ 创作共用协议Attribution-ShareAlike 2.0]
* [http://www.gnu.org/copyleft/fdl.html GNU自由文档许可证]

翻译人员：MillenniumDark

校正人员：farproc

贡献人员：

适用版本：
文章状态：[[翻译完成]]

根据2006-02-20 13:07:56的英文版翻译完成。
----



=== Definition（定义） ===
A checksum is like a signature of data given in a standard fashion. This representation has a fixed length, and is unique for different strings of data. '''Files like this usually ends with md5, md5sum, sha, checksum, sum, or something similar'''

checksum是以标准方式给出的数据的签名。它具有固定的长度，不同的数据串具有各自不同的checksum。'''这一类checksum文件通常以md5、  md5sum、sha、 checksum、sum或者类似的东西结尾。'''

The idea is that it is virtually impossible to modify the data without affecting the signature so that a package cannot be corrupted or manipulated without affecting this signature and once it is corrupted or manipulated, you can know about it.

它的思想是决不可能修改数据而不影响其签名，所以一个包被破坏或被改动后其签名一定会受到影响。同时一旦它被破坏或被改动过，你通过检查签名就会得知。

=== Normal Usage（通常使用） ===
This feature can be used to verify file downloads. If the owner/maintainer/provider of a file creates a checksum, eg an MD5 or SHA file. You can download the file and also download this checksum file. And once the downloads are finished, you can natively calculate your own checksum using the checksum program. These downloaded and calculated values can be verified, thus telling you that the file downloaded is an exact copy of the original. Another use is to verify larger automatic backup solutions, such as common mirroring applications as rsync or wget.

Checksum的这一特性通常用于校验文件下载。如果文件的拥有者、维护者、提供者创建了一个，比如说，MD5或者SHA的Checksum文件, 下载这一文件的使用者可以同时下载这个Checksum文件。一旦下载完成，他/她就可以在本地通过计算得出自己的checksum文件。通过  校验，两者相符，使用者就知道下载所得和预期完全一致。另一个用处是校验巨大的自动备份。也可用于一些常见的镜像软件，比如  rsync和wget。

=== History（历史） ===
This system has been used almost since the dawn of computers. And it is used even today without you knowing it, for example there is CRC checking as you transfer TCP/IP packages to view this page.

几乎在电脑产生的时候这一系统就使用了。如今，它（checksum）依然无处不在，即使你没察觉到；比如，当你传送TCP/IP包来查看本页面时，就使用checksum进行了即时的CRC校验。

==== xmodem ====
----
Xmodem, a popular file-transfer protocol, uses a 1-byte checksum, which is calculated by adding all the ASCII values for all 128 data bytes and ignoring any numeric overflow. The checksum is added to the end of the Xmodem data packet. This type of checksum does not always detect all the errors. In the later versions of the Xmodem protocol, cyclical redundancy check (CRC) is used instead of more rigorous error control. ''(Ref: Dyson, Dictionary of Networking)''

Xmodem，通行的文件传输协议，使用一字节的checksum。这一checksum是这样计算的：将所有128个数据字节的ASCII值相加，忽略所有（相加所得和的）溢出部分的数值。checksum附加在Xmodem数据包的最后。这种checksum并不总能检测出所有错误。在Xmodem协议后续版本中，它被换成cyclical redundancy check (CRC)，以支持更严格的错误控制。''（参见：Dyson，Dictionary of Networking) ''

----

=== Link（链接） ===
[http://freshmeat.net/browse/19/ Freshmeat software repository. [[category:Category]] System Archiving]

[http://ee.tut.fi/~heikki/foss/ckmd5/ chkmd5, a popular md5 checksum verifier]

[http://cfv.sourceforge.net/ cfv, a general checksum creator/checker. This can even verify .torrent files!]

[http://winmd5sum.solidblue.ca/ winmd5sum is a free, open source, easy to use md5 checker for Windows]