About

CRC-32B is the 32-bit Cyclic Redundancy Check defined by the IEEE 802.3 standard, using polynomial 0x04C11DB7 (reflected as 0xEDB88320). It produces an 8-character hexadecimal digest (32 bits) used for error detection in network frames, ZIP archives, PNG chunks, and firmware images. CRC-32B is not cryptographic. It detects accidental corruption but provides zero resistance against intentional tampering. A single flipped bit in a multi-gigabyte file changes the hash entirely, making it effective for integrity verification during transfer. This tool computes the checksum client-side. No data leaves your browser. It processes both raw text (UTF-8 encoded) and binary files. Note: CRC-32B has a collision space of 2³² (4,294,967,296 possible values). For datasets exceeding a few billion entries, collision probability rises per the birthday paradox.

Formulas

The CRC-32B checksum is computed by treating the input as a polynomial over GF(2) and dividing it by the generator polynomial. The reflected table-driven implementation processes one byte at a time:

crc ← 0xFFFFFFFF

for each byte b in input:
index = (crc ⊕ b) ∧ 0xFF
crc = (crc ≫≫≫ 8) ⊕ T[index]

result = crc ⊕ 0xFFFFFFFF

Where T is the precomputed 256-entry lookup table. Each table entry T[i] is generated by iterating 8 times over each index i from 0 to 255:

for j = 0 to 7:
if c ∧ 1:
c = 0xEDB88320 ⊕ (c ≫≫≫ 1)
else:
c = c ≫≫≫ 1

Where c = current value, b = input byte, T = CRC table, ⊕ = bitwise XOR, ≫≫≫ = unsigned right shift, 0xEDB88320 = reflected polynomial of the IEEE 802.3 standard CRC-32.

Reference Data

Algorithm	Polynomial (Normal)	Polynomial (Reflected)	Output Bits	Hex Digits	Common Use
CRC-32B (IEEE 802.3)	0x04C11DB7	0xEDB88320	32	8	Ethernet, ZIP, PNG, gzip
CRC-32C (Castagnoli)	0x1EDC6F41	0x82F63B78	32	8	iSCSI, Btrfs, ext4
CRC-16-CCITT	0x1021	0x8408	16	4	HDLC, Bluetooth, SD cards
CRC-16-IBM	0x8005	0xA001	16	4	Modbus, USB
CRC-8	0x07	0xE0	8	2	ATM HEC, I²C
CRC-64-ECMA	0x42F0E1EBA9EA3693	-	64	16	HDFS, XZ Utils
Adler-32	N/A (sum-based)	N/A	32	8	zlib
MD5	N/A (Merkle - Damgård)	N/A	128	32	Legacy checksums (broken crypto)
SHA-1	N/A (Merkle - Damgård)	N/A	160	40	Git objects (deprecated crypto)
SHA-256	N/A (Merkle - Damgård)	N/A	256	64	TLS, Bitcoin, file integrity
CRC-32/MPEG-2	0x04C11DB7	-	32	8	MPEG-2 transport streams
CRC-32/BZIP2	0x04C11DB7	-	32	8	bzip2 file format
CRC-32/JAMCRC	0x04C11DB7	0xEDB88320	32	8	No final XOR variant
CRC-32/XFER	0x000000AF	-	32	8	XFER protocol

Frequently Asked Questions

In most contexts they are identical. The "B" suffix originates from PHP's hash() function to distinguish the IEEE 802.3 variant (polynomial 0x04C11DB7) from the rarely used CRC-32 variant. CRC-32B matches the checksum used in ZIP, gzip, PNG, and Ethernet. When someone says "CRC-32" without qualification, they almost always mean CRC-32B.

CRC-32B guarantees detection of any single-bit error, any two-bit error, any odd number of bit errors, and any burst error of 32 bits or fewer. For random errors longer than 32 bits, the probability of an undetected error is approximately 1 in 2³² (2.33 × 10⁻¹⁰). It cannot detect intentional (adversarial) modifications because constructing a collision is trivial in constant time.

CRC-32B is a linear function over GF(2). Given any hash value, an attacker can compute a matching input in O(1) time by solving a system of linear equations. It provides zero preimage resistance, zero collision resistance, and zero avalanche guarantees beyond error detection. Use SHA-256 or bcrypt/argon2 for security-sensitive applications.

For text input, no, because UTF-8 encoding produces a fixed byte sequence regardless of platform endianness. For binary files, the CRC is computed over the raw byte stream as stored on disk, so the result is consistent. However, if you serialize multi-byte integers into a buffer manually, you must ensure consistent byte order (typically little-endian for x86) before hashing.

All text is encoded to UTF-8 using the TextEncoder API before hashing. A character like "é" becomes 2 bytes (0xC3 0xA9), and an emoji like "😀" becomes 4 bytes. The CRC-32B is computed over the resulting byte sequence, matching the behavior of PHP's hash('crc32b', $string) and Python's binascii.crc32().

The string "123456789" (9 ASCII bytes) produces CRC-32B cbf43926. An empty input produces 00000000. The single character "a" produces e8b7be43. These are standard test vectors used to verify CRC-32 implementations against the IEEE 802.3 specification.