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.

CRC-32 options

Data

Type text or upload files. Text can be up to 100 MiB, read as UTF-8, and each file up to 2 GiB. Every input is checked on its own.

Variant

ISO-HDLC (the default), AIXM, AUTOSAR, BASE91-D, BZIP2, CD-ROM-EDC, POSIX cksum, CRC-32C (iSCSI), JAMCRC, MPEG-2 or XFER.

Output

An unsigned integer, fixed-width hexadecimal, and the raw 4-byte checksum.

Why CRC-32 has eleven variants

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. CRC-32C (iSCSI), also called Castagnoli, 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 and XFER.

CRC-32 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, SHA-256 or SHA3.

Things to know about CRC-32

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