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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.
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 algorithm: 1 decimal digit sum Damm algorithm: 1 decimal digit Quasigroup operation
The simplest checksum algorithm is the so-called longitudinal parity check, which breaks the data into "words" with a fixed number n of bits, and then computes the bitwise exclusive or (XOR) of all those words. The result is appended to the message as an extra word.
A checksum of a message is a modular arithmetic sum of message code words of a fixed word length (e.g., byte values). The sum may be negated by means of a ones'-complement operation prior to transmission to detect unintentional all-zero messages. Checksum schemes include parity bits, check digits, and longitudinal redundancy checks.
The Fletcher checksum is an algorithm for computing a position-dependent checksum devised by John G. Fletcher (1934–2012) at Lawrence Livermore Labs in the late 1970s. [1] The objective of the Fletcher checksum was to provide error-detection properties approaching those of a cyclic redundancy check but with the lower computational effort ...
Reverse-Engineering a CRC Algorithm Archived 7 August 2011 at the Wayback Machine; Cook, Greg. "Catalogue of parameterised CRC algorithms". CRC RevEng. Archived from the original on 1 August 2020; Koopman, Phil. "Blog: Checksum and CRC Central". — includes links to PDFs giving 16 and 32-bit CRC Hamming distances — (April 2023).
The FNV hash algorithms and reference FNV source code [4] [5] have been released into the public domain. [6] The Python programming language previously used a modified version of the FNV scheme for its default hash function. From Python 3.4, FNV has been replaced with SipHash to resist "hash flooding" denial-of-service attacks. [7]
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