Payment Address Checksum

Overview

Mechanism and important distinctions

A checksum adds redundancy so accidental changes to an encoded address have a chance of being detected. In Ethereum's ERC-55 format, upper- and lowercase letters encode information derived from hashing the address's hexadecimal characters. Bitcoin's Base58Check combines payload data with checksum bytes. These schemes use different constructions and should not be treated as one universal cross-chain validation rule.

Not every blockchain address format has a checksum with the same strength or conventions. For EVM addresses, implementations may accept lower-case forms, which means mixed-case validation cannot be assumed for every input. A checksum never proves the human identity of the owner. Software should report a format error before broadcast, then require independent confirmation that the valid address is the recipient actually intended.

Testing should deliberately modify individual address characters and confirm the wallet rejects malformed values where the chosen format supports detection. Also test an entirely different valid address, which should pass the checksum but require manual recipient verification. Those two tests demonstrate why format checking and beneficiary authentication must be separate steps in a secure checkout process.

Related glossary concepts

Payment Address Normalization; One-Time Payment Address; Crypto Payment Address Screening

Primary reference

ERC-55: Mixed-case checksum address encoding