CRC-32 Calculator (CRC-32 & CRC-32C)
Developer
CRC-32 is a 32-bit cyclic redundancy check — a fast, non-cryptographic checksum used to detect accidental corruption in zip and gzip archives, PNG chunks, Ethernet frames, and many file formats. This calculator implements the standard reflected, table-driven algorithm (initial value 0xFFFFFFFF, final XOR 0xFFFFFFFF) and matches the well-known test vector CRC-32("123456789") = 0xCBF43926. It also offers CRC-32C (Castagnoli, polynomial 0x1EDC6F41), the variant used by iSCSI, SCTP, ext4 metadata, and Intel's SSE4.2 CRC instruction, whose vector for "123456789" is 0xE3069283. Feed it UTF-8 text or raw hex bytes and read the result as lowercase hex, uppercase hex, and an unsigned 32-bit decimal. Use it to verify a download against a published CRC, sanity-check data you're hashing yourself, or debug a checksum mismatch. Everything runs locally — nothing is uploaded. Note: CRC-32 detects accidental errors only; it is not a security hash, so never use it to verify untrusted or adversarial data.
CRC-32 detects accidental corruption, not tampering. For security use a cryptographic hash (SHA-256).
How to use
- Pick the variant (CRC-32 is the common one; CRC-32C for iSCSI/ext4/SSE4.2).
- Choose whether your input is UTF-8 text or hex bytes.
- Type or paste, and copy the hex or decimal result.
Frequently asked questions
- Which CRC-32 is this?
- The default is the standard CRC-32/ISO-HDLC (also called IEEE 802.3, zlib's crc32) — reflected input and output, init 0xFFFFFFFF, final XOR 0xFFFFFFFF, polynomial 0x04C11DB7 (0xEDB88320 reflected). It's what zip, gzip, and PNG use. It matches CRC-32("123456789") = 0xCBF43926.
- What's CRC-32C for?
- CRC-32C uses the Castagnoli polynomial (0x1EDC6F41) and has better error-detection properties. It's used by iSCSI, SCTP, Btrfs/ext4 metadata, and is hardware-accelerated by Intel's SSE4.2 CRC32 instruction. Its vector for "123456789" is 0xE3069283. A CRC computed with one variant won't match the other.
- Can I checksum binary data?
- Yes — switch the input format to Hex and paste the bytes (e.g. 0xDEADBEEF or 'de ad be ef'). The tool also accepts UTF-8 text, which it encodes to bytes before checksumming. Whitespace and an optional 0x prefix are ignored in hex mode.
- Is CRC-32 secure?
- No. CRC-32 is designed to catch random transmission or storage errors, not deliberate tampering — it's trivial to forge a different input with the same CRC. For integrity against an adversary, use a cryptographic hash like SHA-256 instead.
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