CRC-32 Checksum Generator

What is a CRC-32?

A cyclic redundancy check treats your data as a large polynomial, divides it by a fixed one, and keeps the remainder. CRC-32 keeps 32 bits of it. The result catches the error patterns that actually happen on wires and disks: flipped bits, short bursts of damage, truncated transfers.

Pick a variant and hash typed text or uploaded files. You get an unsigned integer, fixed-width hexadecimal, and the raw 4-byte checksum.

Why there are eleven of them

Because CRC-32 is not one algorithm. Variants differ in polynomial, initial value, whether the bits are reflected, and what gets XORed into the final result, and those choices produce completely different checksums over identical data.

ISO-HDLC is what software usually means when it just says CRC-32, and it is the default here. iSCSI is CRC-32C, also called Castagnoli, and is the one modern storage and networking code tends to use because processors implement it directly. The rest exist because a specific format or protocol pinned them: BZIP2, MPEG-2, AIXM, AUTOSAR, BASE91-D, CD-ROM EDC, JAMCRC, XFER.

Use the exact variant the thing you are matching requires. There is no sensible way to guess it from a checksum alone.

Are there alternatives?

CRC-64 gives a wider result for large data sets where 32 bits leaves more collisions than you want. Adler-32 is cheaper to compute and weaker. FNV-1 suits hash tables rather than integrity.

When an attacker is in the picture rather than a faulty cable, none of these apply. Use BLAKE3, SHA256, or SHA3.

Fun facts and more info

The POSIX cksum command incorporates the file length into its calculation, so selecting the CKSUM polynomial over just the input bytes will not necessarily reproduce what the command line prints.

CRC-32 detects accidental corruption and nothing more. Anyone can modify data and recompute a matching checksum, so it offers no protection against deliberate modification, forgery, passwords, or signatures.