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A checksum is a small-sized block of data derived from another block of digital data for the purpose of detecting errors that may have been introduced during its transmission or storage. By themselves, checksums are often used to verify data integrity but are not relied upon to verify data authenticity .
It worked by breaking up the data to be sent into 128-byte packets, adding a 3-byte header and 1-byte checksum footer, and sending the resulting 132-byte packets out in order. The receiving computer recalculated the checksum from the 128 bytes of data, and if it matched the checksum sent in the footer it sent back an ACK , and if it did not ...
SYSV checksum (Unix) 16 bits sum with circular rotation sum8 8 bits sum Internet Checksum: 16 bits sum (ones' complement) sum24 24 bits sum sum32 32 bits sum fletcher-4: 4 bits sum fletcher-8: 8 bits sum fletcher-16: 16 bits sum fletcher-32: 32 bits sum Adler-32: 32 bits sum xor8: 8 bits sum Luhn algorithm: 1 decimal digit sum Verhoeff ...
The Fletcher checksum cannot distinguish between blocks of all 0 bits and blocks of all 1 bits. For example, if a 16-bit block in the data word changes from 0x0000 to 0xFFFF, the Fletcher-32 checksum remains the same. This also means a sequence of all 00 bytes has the same checksum as a sequence (of the same size) of all FF bytes.
The prefix checksum is the 8-bit sum of the four-bit hexadecimal value of the six digits that make up the address and byte count. Data— contains the data to be transferred, followed by a 2 character (1 byte) checksum. The data checksum is the 8-bit sum, modulo 256, of the 4-bit hexadecimal values of the digits that make up the data bytes. [4] [2]
This is two-error-correcting, being of minimum distance 5. This adds 4 bytes of redundancy, forming a new frame: . The resulting 28-symbol codeword is passed through a (28.4) cross interleaver leading to 28 interleaved symbols.
The Internet checksum, [1] [2] also called the IPv4 header checksum is a checksum used in version 4 of the Internet Protocol (IPv4) to detect corruption in the header of IPv4 packets. It is carried in the IP packet header , and represents the 16-bit result of summation of the header words.
cksum is a command in Unix and Unix-like operating systems that generates a checksum value for a file or stream of data. The cksum command reads each file given in its arguments, or standard input if no arguments are provided, and outputs the file's 32-bit cyclic redundancy check (CRC) checksum and byte count. [1]