How is CRC-32C different from regular CRC-32?

They use different generator polynomials. Standard CRC-32 (used by zlib, PNG, and Ethernet) uses 0x04C11DB7, while CRC-32C uses the Castagnoli polynomial 0x1EDC6F41. The polynomials produce completely different checksums for the same data.

What is the correct check value for CRC-32C?

For the ASCII string "123456789", CRC-32C must produce 0xE3069283. This tool returns that exact value, confirming the Castagnoli polynomial, reflection, and final XOR are implemented correctly.

Where is CRC-32C actually used?

It is the integrity check for iSCSI, SCTP, the ext4 and Btrfs filesystems, and many NVMe and storage paths. Modern x86 CPUs include an SSE 4.2 instruction that computes it in hardware, which is why it was chosen for high-throughput protocols.

Why are the parameters reflected?

CRC-32C uses reflected input and output and an initial value of 0xFFFFFFFF with a final XOR of 0xFFFFFFFF. Reflection matches how data is shifted least-significant-bit first on the wire and lets the bytewise table method run efficiently.

Can CRC-32C detect malicious changes?

No. Like all CRCs it only catches accidental corruption such as bit flips or dropped bytes. An attacker can craft data with any desired CRC, so use a cryptographic hash or MAC where tampering is a concern.

CRC-32C (Castagnoli) Checksum

What CRC-32C is

CRC-32C is a 32-bit cyclic redundancy check based on the Castagnoli polynomial, chosen for storage and network protocols because it has strong error-detection properties and can be computed in hardware.

How it works

The CRC register is initialised to 0xFFFFFFFF. Each input byte is XORed into the low byte of the register, then the register is shifted right eight times; each time a 1 bit is shifted out, the reflected polynomial 0x82F63B78 (the bit-reversal of 0x1EDC6F41) is XORed back in. After the final byte, the register is XORed with 0xFFFFFFFF to produce the result. Because both input and output are reflected, the whole computation runs least-significant-bit first.

This calculator precomputes a 256-entry table from the polynomial and folds one byte at a time through it — the same byte-slicing approach the Linux kernel and Intel’s CRC libraries use.

Example and notes

The standard test vector 123456789 yields 0xE3069283; matching this value is the quickest way to confirm a CRC-32C implementation. Switch to Hex bytes to checksum binary data such as a disk block or a network segment payload.

Do not confuse CRC-32C with the more common CRC-32 used by zlib, gzip, and PNG — they share the name “CRC-32” but use different polynomials and will never agree on the same input. CRC-32C protects only against accidental corruption and is not a security primitive.