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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 IPv4 packet header, and represents the 16-bit result of the summation of the header words. [3] The IPv6 protocol does not use header checksums.
The method used to compute the checksum is defined in RFC 768, and efficient calculation is discussed in RFC 1071: Checksum is the 16-bit ones' complement of the ones' complement sum of a pseudo header of information from the IP header, the UDP header, and the data, padded with zero octets at the end (if necessary) to make a multiple of two octets.
The content of such spam may often vary in its details, which would render normal checksumming ineffective. By contrast, a "fuzzy checksum" reduces the body text to its characteristic minimum, then generates a checksum in the usual manner. This greatly increases the chances of slightly different spam emails producing the same checksum.
Fast-Hash [3] 32 or 64 bits xorshift operations SpookyHash 32, 64, or 128 bits see Jenkins hash function: CityHash [4] 32, 64, 128, or 256 bits FarmHash [5] 32, 64 or 128 bits MetroHash [6] 64 or 128 bits numeric hash (nhash) [7] variable division/modulo xxHash [8] 32, 64 or 128 bits product/rotation t1ha (Fast Positive Hash) [9] 64 or 128 bits
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.
In this example, we shall encode 14 bits of message with a 3-bit CRC, with a polynomial x 3 + x + 1. The polynomial is written in binary as the coefficients; a 3rd-degree polynomial has 4 coefficients (1x 3 + 0x 2 + 1x + 1). In this case, the coefficients are 1, 0, 1 and 1. The result of the calculation is 3 bits long, which is why it is called ...
For computing the checksum UDP-Lite uses the same checksum algorithm used for UDP (and TCP). [1] Modern multimedia codecs, like G.718 and Adaptive Multi-Rate (AMR) for audio and H.264 and MPEG-4 for video, have resilience features already built into the syntax and structure of the stream. This allows the codec to (a) detect errors in the stream ...
The TCP protocol's alternate checksum has Fletcher-16 with a 256 modulus, [3] as do the checksums of UBX-* messages from a U-blox GPS. [4] Which modulus is used is dependent on the implementation. Example calculation of the Fletcher-16 checksum