No CRC64 implementation equal to CommonCrypto?

Question

I am porting some code from C on OSX to C# that uses CommonCrypto with the kCN_CRC_64_ECMA_182 CRC64 implementation. For example, using CommonCrypto the CRC would be computed with:

CNCRC(kCN_CRC_64_ECMA_182, bytes, bytesLen, &crcResult)

This outputs the correct value. When using the C# library HashLib (or any other code), the output is completely different, for example, the equivalent to the above using HashLib would be:

var checksum = HashFactory.Checksum.CreateCRC64(0x42F0E1EBA9EA3693UL); // ECMA 182 var result = checksum.ComputeBytes(bytes);

Any ideas? Is there an implementation in C# that is equivalent to Apple's CommonCrypto in terms of output?

Answer 1

Here is some simple C code to compute the ECMA-182 CRC:

#include <stddef.h>
#include <stdint.h>

#define POLY UINT64_C(0x42f0e1eba9ea3693)
#define TOP UINT64_C(0x8000000000000000)

/* Return crc updated with buf[0..len-1].  If buf is NULL, return the initial
   crc.  So, initialize with crc = crc64_ecma182(0, NULL, 0); and follow with
   one or more applications of crc = crc64_ecma182(crc, buf, len); */
int64_t crc64_ecma182(int64_t crc, unsigned char *buf, size_t len)
{
    int k;

    if (buf == NULL)
        return 0;
    while (len--) {
        crc ^= (uint64_t)(*buf++) << 56;
        for (k = 0; k < 8; k++)
            crc = crc & TOP ? (crc << 1) ^ POLY : crc << 1;
    }
    return crc;
}

I think HashLib is simply wrong, judging by what I found on github. It is doing the CRC reflected, whereas the CRC64 defined in ECMA-182 is not reflected.