CRC32 and Checksum Calculator

About the CRC32 and Checksum Calculator

A checksum is a short number calculated from data, so that damaged or changed data gives a different number. A cyclic redundancy check, or CRC, treats the data as a long binary number and divides it by a fixed polynomial, keeping the remainder. Each CRC is defined by its width, its polynomial, its starting value, whether bits are reflected and a final XOR, and different combinations give different answers for the same data, which is why "CRC-16" alone is ambiguous. The catalogue check value for each model is its result for the nine characters 123456789: CRC-32 gives CBF43926, CRC-32C gives E3069283, CRC-16/ARC gives BB3D and CRC-8/SMBUS gives F4. CRC-32 is used by ZIP, PNG, gzip and Ethernet, and CRC-32C by iSCSI and many storage systems. Adler-32 is the checksum at the end of a zlib stream. It keeps two running sums modulo 65521 and is faster than a CRC but weaker, especially on short data: the text Wikipedia gives 11E60398. Text is converted to UTF-8 bytes before the checksum is taken, so accented letters and emoji count as several bytes, and you can switch to hex input to checksum raw bytes. None of these are secure hashes. They are built to catch accidental damage, and anyone can change data and adjust it to keep the same checksum, so use SHA-256 or another cryptographic hash when tampering matters.