A method for determining data packet checksum after data modification

Abstract

This invention discloses a method of method of determining the packet check-sum of the modified data, the method includes: (A) Add all the data before being modified corresponding to the related modified data segments in the packet, and obtain a sum value x; (B) Add all the modified data corresponding to the related modified data segments in the packet, and obtain a sum value y; (C) Obtain the check-sum Z of the packet before being modified; (D) Obtain the check-sum after being modified based on the value of the equation: (M<<k)+(Z-M)-x+y, wherein, (M<<k) means that moving left the M for k bits, k is the number of the bits of the data segments, the M is the number of the related modified data segments. The usage of this invention can simplify the priority method of determining the packet check-sum of the modified data, and it can save the resource of the processor, improve the efficiency of working.

Description

technical field [0001] The invention relates to data check technology, in particular to a method for determining the check sum of data packets after data modification. Background technique [0002] The checksum is used to verify the consistency of data from the source host to the destination host. The 16-bit checksum is used in the TCP / IP protocol suite, and the checksum of each part has its own meaning. In the prior art, the basic algorithm for determining the 16-bit checksum includes the following steps: [0003] a. Divide all the data to be used to determine the checksum into N segments of 16 bits. If the number of bytes is not an even number, add a byte of all 0 padding. This padding is only to determine the checksum. Discard it when it is determined; [0004] b. Sum the N data segments to obtain a sum value that may be greater than 16 bits; [0005] c. Add the carry value greater than 16 bits to the lower 16 bits according to the above rules, if a carry is generated...

AI Technical Summary

Problems solved by technology

[0012] The disadvantage of the above method is: when the data in the TCP data packet is changed, the change includes the modification of the source and destination IP addresses of the pseudo-header, and the checksum needs to be re-determined according to the above method. It is necessary to recalculate the checksum based on all the data according to the above method, thus wasting processor resources and resulting in low efficiency. This shortcoming is more obvious when the TCP data packet is long

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