CRC32 Checksum ieee 802.3

What this tool does

CRC32 produces a 32-bit value from the remainder of a polynomial division, written as eight hexadecimal characters. This tool uses the IEEE 802.3 polynomial, the same one used by Ethernet, ZIP, PNG, and gzip.

CRC is an error-detecting code rather than a cryptographic hash. Its purpose is to catch bits that flip during transmission or storage, and it detects burst errors with very high probability. Computation is a simple table lookup and XOR, which makes it fast in software and easy to implement in hardware.

It offers no protection against deliberate manipulation, because constructing data that yields a chosen CRC value is mathematically straightforward. That makes it appropriate for asking whether a file was corrupted, and inappropriate for asking whether a file was tampered with.

When to use it

Use it to check the checksum recorded in an archive or image, to build a fast key for narrowing down duplicate candidates among many strings, to validate a checksum routine while implementing a protocol, or to confirm data survived a transfer intact.

Input and output examples

Notes and limitations

CRC32 must not be used for security verification. Data can be crafted to produce a specific CRC, so it cannot prove integrity or replace a signature; use SHA-256 or HMAC for that. The 32-bit space also holds only about four billion values, so collisions between different inputs occur in practice once you pass a few hundred thousand records. When using it for duplicate detection, compare the original data again whenever CRCs match.

Frequently asked questions