I've now programmed a solution for the above mentioned problem which was easier than I initially thought it would be. I found several articles about how one can forge a CRC. That means how to patch data that way that the calculated CRC value will have a predefined value. Using...

To use a byte-wise CRC routine, you need to convert your sequence of bits into a sequence of bytes. The order of the bits depends on the order of the CRC, which in this case (CCITT-false) is not reflected, so you consider the stream of bits to be most significant...

You can create the function yourself, this is a working example for PostgreSQL 9.4 CREATE OR REPLACE FUNCTION crc32(text_string text) RETURNS bigint AS $$ DECLARE tmp bigint; i int; j int; byte_length int; binary_string bytea; BEGIN IF text_string = '' THEN RETURN 0; END IF; i = 0; tmp =...

I wrote the code you're linking to, so I will attempt to answer your questions. Using ~0L. This is necessary because the algorithm works on 32-bit numbers, and the Arduino's code uses 16-bit numbers by default. The "L" suffix tells the compiler that the value is "long", so it does...

reverse-engineering,checksum,crc,crc16

Here you go, in C: #include <stddef.h> unsigned crc16old(unsigned crc, unsigned char *buf, size_t len) { int k; if (buf == NULL) return 0xffff; while (len--) { crc ^= *buf++; for (k = 0; k < 8; k++) crc = crc & 1 ? (crc >> 1) ^ 0x8408 :...

This tutorial (also here, here, and here for those who will complain about link rot), in particular "10. A Slightly Mangled Table-Driven Implementation", explains well the optimization to avoid feeding an extra 32 zero bits at the end. The bottom line is that you feed the bits into the end...

algorithm,hash,gzip,digital-signature,crc

The CRC in zip files is mainly used to make sure that the file is not damaged during storage or transit. It is not used to provide authenticity or protect against files being changed by an attacker. So the cryptographic safety is not required. Cryptographic hashes do provide the same...

If you look at the RevEng 16-bit CRC Catalogue, you see that there are two different CRCs called "CCITT", one of which is labeled there "CCITT-False". Somewhere along the way someone got confused about what the CCITT 16-bit CRC was, and that confusion was propagated widely. The two CRCs are...

The problem is on these lines: proc crc8{} { Because Tcl really cares about putting spaces between things, and treats newline as a statement terminator, you have to write them as: proc crc8 {} { (You could also use a backslash at the end of the line to prevent the...

This is what I managed to put together for CRC-8. Still, I cannot fully understand how the polynomial is produced, especially why we should/could use the reversed version! I also miss a CRC-16, CRC-32 and maybe a CRC-64 complete example as the one I provide below. Hopefully someone else will...

update() is for incrementally calculating the checksum over a sequence of bytes. Your code calculates the crc32 over the concatentation of all the ciphertexts provided to update() on the same CRC32 object. Try c.reset() c.update(ciphertext); System.out.println("Now ciphertext = " + ciphertext + ", and CRC = " + c.getValue()); ...

Refer to this answer: Convert a string representation of a hex dump to a byte array using Java? Add the hexStringToByteArray function to your code and call it like this: byte[] bytes = hexStringToByteArray(str); ...

After a bit more searching I found this: http://reveng.sourceforge.net/crc-catalogue/1-15.htm#crc.cat-bits.5 It provides the following information (copied to ensure that it doesn't disappear): In case it is not clearly visible, the relevant information is: width=5 poly=0x09 init=0x09 refin=false refout=false xorout=0x00 check=0x00 name="CRC-5/EPC" As you can see, they don't just give the information...

This code: #include <stdio.h> #define POLY 0xa001 unsigned crc16(unsigned crc, unsigned char *buf, size_t len) { while (len--) { crc ^= *buf++; crc = crc & 1 ? (crc >> 1) ^ POLY : crc >> 1; crc = crc & 1 ? (crc >> 1) ^ POLY : crc...

This line is incorrect: res = (tmp & 0xff) + (tmp >> 8); In the original code CRC is an uint8_t, so the result of that calculation should be in the range 0-255. Hence you want this instead: res = ((tmp & 0xff) + (tmp >> 8)) & 0xff; What's...

Koopman's notation represents a polynomial, but it is not a polynomial. You cannot use it as an input to the lookup table generator you used. Your first table is useless, since the implied polynomial does not have a low bit of 1. Koopman's notation depends on the fact that all...

Yes. You can see how in zlib's crc32_combine(). If you have two sequences A and B, then the pure CRC of AB is the exclusive-or of the CRC of A0 and the CRC of 0B, where the 0's represent a series of zero bytes with the length of the corresponding...

The appending the CRC thing only works for "pure" CRCs without pre and post-conditioning. Most real world CRCs however have pre and post-conditioning, mainly so that the CRC of strings of zeros are not zero. The way to check a CRC is the same as any other check value. You...

python,algorithm,hash,crc,crc32

You can use CRC RevEng to search for CRCs. This one turns out to be easy, as it is a standard CRC: % ./reveng -w 32 -s 2630303a30323a39423a39333a34413a38342631323926315d2852c5 width=32 poly=0x04c11db7 init=0xffffffff refin=false refout=false xorout=0x00000000 check=0x0376e6e7 name="CRC-32/MPEG-2" % ./reveng -w 32 -s 2646463a46463a46463a46463a46463a46462631323826319546841e width=32 poly=0x04c11db7 init=0xffffffff refin=false refout=false xorout=0x00000000 check=0x0376e6e7 name="CRC-32/MPEG-2"...

You can find a complete implementation of the CRC calculation (and PNG encoding in general) in this public domain code: http://upokecenter.dreamhosters.com/articles/2011/04/png-image-encoder-in-c/ static uint[] crcTable; // Stores a running CRC (initialized with the CRC of "IDAT" string). When // you write this to the PNG, write as a big-endian value static...

I was able to produce the same checksum with implementation like below: define('CRC16POLYN', 0x1021); function CRC16Normal($buffer) { $result = 0xFFFF; if (($length = strlen($buffer)) > 0) { for ($offset = 0; $offset < $length; $offset++) { $result ^= (ord($buffer[$offset]) << 8); for ($bitwise = 0; $bitwise < 8; $bitwise++) {...

You're receiving ArrayIndexOutOfBoundException probably, so I think the hex value might have zero in its most significant nibble. Try to find out those values(x) and check whether (x >>> 12) == 0 or (x & 0xf000) == 0. If this returns true, you can pad your string with necessary number...

crc,crc32,crc16,error-detection,crc64

The polynomial chosen determines the error detection capability of the CRC. This capability is measured in Hamming Distance, which is the minimum number of bit errors that can be introduced in the message while leaving the CRC unchanged. This would be a false positive, where the CRC says the message...

There are 2 solutions: 1. Solution: You can compute the CRC over all your input data and append zeros at the end where the CRC will be inserted. The receiver calculates the CRC with the same algorithmn over all data (payload + crc). The CRC is zero if all data...

Try it like this: function crc8_calc($hex_string) { $bin_data = pack('H*',$hex_string); $bin_length = strlen($bin_data); $CRC = 0; $tmp = 0; $pos = 0; while($bin_length>0) { $tmp = $CRC << 1; $tmp = $tmp + ord($bin_data[$pos]); //Added ord $CRC = ($tmp + ($tmp >> 8)) & 0xFF; $bin_length --; $pos++ ; }...

CRC implementations use tables for speed. They are not required. Here is a short CRC32 using either the Castagnoli polynomial (same one as used by the Intel crc32 instruction), or the Ethernet polynomial (same one as used in zip, gzip, etc.). #include <stddef.h> #include <stdint.h> /* CRC-32C (iSCSI) polynomial in...

Yes. You can see how in the implementation of crc32_combine() in zlib. It takes crc1, crc2, and len2, where len2 is the number of bytes in the block on which crc2 was calculated. It takes O(log(len2)) time. The combination can be repeated for following blocks. The approach is to continue...

What will happen is that the frame will be considered valid by the data link layer and its payload will be passed to the upper layers. The upper layers might have their own error detection mechanisms (e.g. TCP/IP checksum) so the might detect the error themselves and throw out the...

Works for me, all I did is pad the dividend out to 32bits 10101001101000001010000000000000 11101101001 01000100100000001010000000000000 11101101001 00110010000100001010000000000000 11101101001 00001001010110001010000000000000 11101101001 00000111100010101010000000000000 11101101001 00000000111000111010000000000000 11101101001 00000000000011101000000000000000 11101101001 00000000000000000101001000000000 11101101001 00000000000000000010010010010000 11101101001 00000000000000000001111111011000 11101101001...

The result 0x29b1 is for the "false" CCITT CRC-16. That CRC uses the polynomial unreflected, so you would use 0x1021 instead. See this list of CRC definitions. You also need to change the initialization of the zero operator, and account for the initialization of the CRC. Below is code (in...