Checksum

n. final check, examination of several of the bits which are transferred in order to discover transfer errors (Computers)

This article is about checksums calculated using addition. The term "checksum" is sometimes used in a more general sense to refer to any kind of redundancy check. Checksums on decimal numbers are discussed under check digit. A checksum is a form of redundancy check, a simple way to protect the integrity of data by detecting errors in data that are sent through space (telecommunications) or time (storage). It works by adding up the basic components of a message, typically the asserted bits, and storing the resulting value. Anyone can later perform the same operation on the data, compare the result to the authentic checksum, and (assuming that the sums match) conclude that the message was probably not corrupted.
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Noun
1. a digit representing the sum of the digits in an instance of digital data; used to check whether errors have occurred in transmission or storage
(hypernym) confirmation, verification, check, substantiation

1. The sum of a group of data items, which sum is used for checking purposes. Note 1: A checksum is stored or transmitted with the group of data items. Note 2: The checksum is calculated by treating the data items as numeric values. Note 3: Checksums are used in error detecting and correcting. 2. [The] value computed, via some parity or hashing algorithm, on information requiring protection against error or manipulation. Note: Checksums are stored or transmitted with data and are intended to detect data integrity problems. [NIS]

<storage, communications> A computed value which depends on the contents of a block of data and which is transmitted or stored along with the data in order to detect corruption of the data. The receiving system recomputes the checksum based upon the received data and compares this value with the one sent with the data. If the two values are the same, the receiver has some confidence that the data was received correctly.
The checksum may be 8 bits (modulo 256 sum), 16, 32, or some other size. It is computed by summing the bytes or words of the data block ignoring overflow. The checksum may be negated so that the total of the data words plus the checksum is zero.
Internet packets use a 32-bit checksum.
See also digital signature, cyclic redundancy check.
(1996-03-01)