Checksum
CRC-64
A 64-bit cyclic redundancy check. The wider output catches longer error bursts than CRC-32 and reduces the collision rate on multi-GiB files to a negligible level. Two common polynomials live in production code, and they produce different digests for the same input , pick deliberately.
At a glance
| Output | 64 bits (16 hex chars) |
|---|---|
| Operation | Polynomial division in GF(2) |
| Throughput | ~3-7 GiB/s with SIMD |
| Status | Non-cryptographic; accidental-corruption detection only |
The two common variants
| Name | Polynomial | Where |
|---|---|---|
| CRC-64 (ISO) | 0x000000000000001B | ISO 3309, tape archives, some checksum tools |
| CRC-64 (ECMA-182) | 0x42F0E1EBA9EA3693 | XZ utils, .xz archives |
Where it shows up
- XZ utils / .xz archives , ECMA-182 CRC-64 per block.
- Tape archives, magnetic disks , ISO 3309 polynomial.
- Distributed storage , quick integrity checks for large objects.
- Bioinformatics tools , CRC-64 of a sequence as a quick ID.
vs CRC-32
CRC-64 catches all single-bit errors, all double-bit errors within a span of 264−1 bits, and all error bursts up to 64 bits. The expected collision rate on random inputs is 232, so it’s comfortably overspecified for any single-file integrity check.
References
Visualize
CRC-64 on your input
11 bytes · 0-bit digest
Hex digest
Bit grid (0 bits, teal = 1, slate = 0)
Byte pixel art (0 bytes, hue = byte value mod 360°)
Avalanche , flipping the lowest bit of the first input byte changed 0 of 0 output bits
Quick quiz
Test yourself on crc-64
10 multiple-choice questions. Pick an answer for each, then submit to see explanations.
Q1.What is the output size of CRC-64?
Q2.Which polynomial does XZ utils use for CRC-64?
Q3.ISO 3309 polynomial value:
Q4.Are CRC-64 and CRC-32 cryptographic?
Q5.Expected random-collision rate for CRC-64:
Q6.Two .xz archives produce CRC-64s using:
Q7.Could CRC-64 reasonably authenticate a remote API request?
Q8.Which of these uses CRC-64?
Q9.Does CRC-64 protect against bit-flips in long error bursts better than CRC-32?
Q10.Which compression / archive format does NOT typically use CRC-64?