Checksum

In computer science, a checksum (English checksum ) is a simple measure to approximate ensuring data integrity during data transmission or storage. It is used primarily for data backup and data transmission.

Simple procedures

There are different checksum. The simple method always run off to a same scheme:

Will be bits, bytes, or any other fundamental component of a data message is multiplied by a certain factor, and then summed up in order. The resulting value is then saved as a checksum or transferred. The recipient of the message can also calculate a checksum and compare it with the co-transmitted checksum of the transmitter from the data. If the two checksums are different, there is a transmission error and the message must be repeated. If the two checksums are identical, the message has been transmitted with a high probability of correct.

A simple example of a checksum is the checksum of the digits of a number. However, with this method, for example, be " transposed digits ", ie a common error in the entry of numerical information by people, not detected. These errors arise, inter alia, due to the expression of numbers in the German language, in which the one to be called before the tens. For example, thirty-seven, seven then three.

Checksum, which operate with a certain weighting of the individual summands are quite safe against accidental changes, such Zeichenvertauschungen, doublings or omissions. They are for example used in the ISBN (International Standard Book Number ) and the EAN code.

More complex procedures

The term " checksum " is also used for more sophisticated testing methods that perform complex calculations instead of the simple sum of the data values ​​, such as the Cyclic Redundancy Check ( CRC Sheet ). A Cyclic Redundancy Check is used instead of simple addition of a polynomial, and is generally effective in the detection of random errors as a primitive checksum.

Although a conventional checksum is useful to protect against inadvertent changes, it does not provide security against data plan changes ( manipulation), as it is trivial to bypass. It is often necessary therefore, instead of a simple check summing cryptographically stronger algorithms such as one-way hash functions (eg, message digests ) to use. These continue to form the basis of electronic signatures dar.

Related Topics

• Checksums are part of most error correction procedures.
• Mathematical model of many checksums is the dihedral group.