# Check total

in computer science is **a check total** (English: checksum) a simple measure for the guarantee of data integrity during the data communication or - storage. It is used mainly during the data protection and during the data communication.

There are different check total procedures. The simple procedures always run according to a same patternoff:

Bits, bytes or another fundamental component of data of a message by a certain factor are multiplied and summed afterwards after the order. The arising value is then along-stored or transmitted as well as check total. The receiver of the message can from the datalikewise compute a check total and these with the transmitted as well check total of the transmitter compare. If the two check totals are different, a transfer error is present and the message must be repeated. If the two check totals are identical, the message with high probability was correctly transferred.

A simple examplefor a check total is the checksum of the numbers of a number.

Check total procedures, which work with a certain weighting of the individual addends, are quite safe in relation to coincidental changes, z. B. Indication permutations, - doublings or - omissions. It for example applied with the ISBN (international standard Book NUMBER) andthe EAN - Code.

The term „check total “is used also for aufwändigere testing methods, which make more complex computations in place of the simple summation of the data values, so z. B. for the (carriage return character) - procedures. A (carriage return character) used instead of simple addition a polynomial division and is generally more effective with the recognitionof accidental errors as a primitive check total.

Although a conventional check total is useful, in order to protect against unintentional changes, it offers no in relation to to security intends data changes (manipulation), since it is to be gone around trivially. Is therefore often necessary, in place of a simple check total procedure kryptografisch stronger algorithms, howOne-way Hash - algorithms (z. B. Message Digests) to use. These represent further the basis of electronic signatures .

*See also:* Hash function and the procedures specified there.

## Web on the left of

- Jacksum - platform-independent program for the calculation and verifying of various check totals (with Java - source text)
- VisualHash- Check total formulas for the check total computation of different systems compute Windows program with graphic surface for the calculation of various check totals
- (open SOURCE, needs .NET 1,1) for German identity card (open SOURCE
- program inclusive source code and algorithm)