Dev & Computing · CRC 校验（Cyclic Redundancy Check） · Updated 2026-10-25
What Is CRC Checksum?
Definition
CRC treats data as one large binary number, divides it by an agreed generator polynomial, and appends the remainder as the check value; the receiver recomputes and compares — any mismatch means corruption. CRC32 is used in ZIP, PNG and Ethernet frames. Its math reliably detects all 1- and 2-bit errors, all odd-bit errors and burst errors up to 32 bits. CRC detects accidental damage, not tampering — an attacker can recompute the CRC, which is the job of cryptographic hashes (SHA-256).
Formula
CRC = remainder of data ÷ generator polynomial; e.g. CRC-32 uses 0x04C11DB7
Worked Example
After downloading a 4.7 GB Linux ISO, matching the locally computed CRC32 against the published value proves no bit flipped in transit; one wrong bit means re-downloading. That is exactly its value as an accidental-damage detector.
Common Misconception
Using CRC for tamper-proofing or password checking — CRC is neither collision- nor forgery-resistant; an attacker can craft a malicious file with identical CRC. Security contexts require cryptographic hashes like SHA-256.
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