Fletcher-16 Checksum

Calculate the two-sum Fletcher-16 checksum of UTF-8 text modulo 255.

Description

Calculate Fletcher-16 Checksum over UTF-8 text and display the result as uppercase hexadecimal.

Fletcher-16 Checksum is intended for interoperability and accidental-error detection. Fletcher-16 maintains two sums modulo 255: one accumulates bytes and the other accumulates the first sum. Their two 8-bit residues form the result.^[1]

When to use Fletcher-16 Checksum

Use this checksum only when a file format, device, protocol, or published test vector specifies the same named profile and parameters. Profiles with the same width can still produce unrelated results.

How Fletcher-16 Checksum works

Fletcher-16 maintains two sums modulo 255: one accumulates bytes and the other accumulates the first sum. Their two 8-bit residues form the result.^[1]

How the Fletcher-16 function processes input

Encode the entered text as UTF-8 bytes.
Process the bytes with the selected algorithm and its exact parameters.
Render the result in the canonical textual form shown by the tool.

Limitations and assumptions

Checksums are not collision-resistant and must not be used as digital signatures or security proofs.
Text is encoded as UTF-8; a checksum over a file's raw bytes can differ.
Every CRC parameter—including reflection and initialization—must match the other implementation.

Alternative or Complementary approaches

Use a cryptographic hash such as SHA-256 when malicious modification is in scope. Use the custom CRC calculator when a documented profile is not available as a preset.

References

Fletcher's checksum — Wikipedia contributors

Similar or alternative tools

CRC-32 Checksum
Use the common ISO-HDLC CRC-32 profile.
SHA-256 Hash Generator
Use a cryptographic digest for adversarial integrity.