checksum | 易学教程

TCP Checksum calculation doesn't match with the the wireshark calculation

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问题 I am experiencing a problem where the tcp checksum generated by the sample program (copied below) doesn't match with the checksum calculated by wireshark. Can some one please point me where i am going wrong. Here i tried two ways tcp_checksum get_ipv6_udptcp_checksum. with both these, getting two different values and both are not matching with the wireshark value. I am copying here the IP and TCP Header details. IP Header: 0000 60 00 00 00 00 2a 06 80 10 80 a2 b1 00 00 00 00 0010 00 00 00 00

Check Duplicate File content using Java

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We have a 150 Gb data folder. Within that, file content is any format (doc, jpg, png, txt, etc). We need to check all file content against each other to check if there are is duplicate file content. If so, then print the file path name list. For that, first I used ArrayList<File> to store all files, then used FileUtils.contentEquals(file1, file2) method. When I try it for a small amount of files(Folder) it's working but for this 150Gb data folder, it's not showing any result. I think first storing all files in an ArrayList makes the problem. JVM Heap problem, I am not sure. Anyone have better

Checksumming large swathes of prime numbers? (for verification)

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问题 Are there any clever algorithms for computing high-quality checksums on millions or billions of prime numbers? I.e. with maximum error-detection capability and perhaps segmentable? Motivation: Small primes - up to 64 bits in size - can be sieved on demand to the tune of millions per second, by using a small bitmap for sieving potential factors (up to 2^32-1) and a second bitmap for sieving the numbers in the target range. Algorithm and implementation are reasonably simple and straightforward

Confirming file content against hash

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问题 I have a requirement to 'check the integrity' of the content of files. The files will be written to CD/DVD, which might be copied many times. The idea is to identify copies (after they are removed from Nero etc.) which copied correctly. Am rather new to this, but a quick search suggests that Arrays.hashCode(byte[]) will fit the need. We can include a file on the disk that contains the result of that call for each resource of interest, then compare it to the byte[] of the File as read from

xor all data in packet

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I need a small program that can calculate the checksum from a user input. Unfortunately, all I know about the checksum is that it's xor all data in packet. I have tried to search the net for an example without any luck. I know if I have a string: 41,4D,02,41,21,04,02,02,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00 This should result in a checksum of 6A. Hopefully someone could help me. If someone has an example writen in Python 3, could also work for me If i understand "xor all data in packet" correctly, then you should do something like this: #include

How to calculate md5 checksum on directory with java or groovy?

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问题 I am looking to use java or groovy to get the md5 checksum of a complete directory. I have to copy directories for source to target, checksum source and target, and after delete source directories. I find this script for files, but how to do the same thing with directories ? import java.security.MessageDigest def generateMD5(final file) { MessageDigest digest = MessageDigest.getInstance("MD5") file.withInputStream(){ is -> byte[] buffer = new byte[8192] int read = 0 while( (read = is.read

Best 8-bit supplemental checksum for CRC8-protected packet

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I'm looking at designing a low-level radio communications protocol, and am trying to decide what sort of checksum/crc to use. The hardware provides a CRC-8; each packet has 6 bytes of overhead in addition to the data payload. One of the design goals is to minimize transmission overhead. For some types of data, the CRC-8 should be adequate, for for other types it would be necessary to supplement that to avoid accepting erroneous data. If I go with a single-byte supplement, what would be the pros and cons of using a CRC8 with a different polynomial from the hardware CRC-8, versus an arithmetic

More idiomatic way to calculate GS1 check digit in Clojure

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I am trying to calculate a GS1 check digit and have come up with the following code. The algorithm for calculating a check digit is: Reverse the barcode Drop the last digit (calculated check digit) Add the digits together with first, third, fifth, e.t.c. digit multiplied by 3 and even digits multiplied by 1. Subtract the sum from nearest equal or higher multiple of ten It sounds simple typed out but the solution I came up with seemed a bit inelegant. It does work but I want to know if there is a more elegant way of writing this. (defn abs "(abs n) is the absolute value of n" [n] (cond (not

What algorithm to use to calculate a check digit?

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问题 What algorithm to use to calculate a check digit for a list of digits? The length of the list is between 8 and 12 digits. see also: How to generate a verification code/number? 回答1: The Luhn algorithm is good enough for the credit card industry... 回答2: As RichieHindle points out, the Luhn algorithm is pretty good. It will detect (but not correct) any one error or transposition (except a transposition of 0 and 9). You could also consider the algorithm for ISBN check digits, although for old

Is Fletchers16 checksum suitable for small data?

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Using the straight forward implementation on wikipedia Fletcher's checksum we get the same checksum for data such as "BCA" and "CAB" as well as "BAC" and "ACB". Is this expected? Should not the Fletcher16 checksum account for the order of the blocks? The deficiency can easily be fixed by OR'ing the index with the data as shown in the code below.... uint16_t fletcher16( uint8_t *data, int count ) { uint16_t sum1 = 0; uint16_t sum2 = 0; int index; for( index = 0; index < count; ++index ) { //sum1 = (sum1 + data[index]) % 255; // Original sum1 = (sum1 + index | data[index]) % 255; // The "fix"