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A checksum is an error-detection method in a the transmitter computes a numerical value according to the number of set or unset bits in a message and sends it along with each message frame. At the receiver end, the same checksum function (formula) is applied to the message frame to retrieve the numerical value. If the received checksum value matches the sent value, the transmission is considered to be successful and error-free.
A checksum may also be known as a hash sum.
A mismatched checksum shows that the entire message has not been transmitted. TCP/IP and User Datagram Protocol (UDP) provide a checksum count as one of their services.
The procedure of generating checksums from messages is called a checksum function and is performed using a checksum algorithm. Efficient checksum algorithms produce different results with large probabilities if messages are corrupted. Parity bits and check digits are special checksum cases suitable for tiny blocks of data. Certain error-correcting codes based on checksums are even capable of recovering the original data.
The most commonly-used checksum tools include: