EIP 55: Mixed-case checksum address encoding

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Note: The following is an excerpt from the official Ethereum site. It is provided here as a connivence and is not authoritative. Refer to the original document as the authoritative reference.

Data sheet for Mixed-case checksum address encoding

Title	Mixed-case checksum address encoding
Author	Vitalik Buterin, Alex Van de Sande
Status	Final
Created	2016-01-14
Description	http://eips.ethereum.org/EIPS/eip-55
Specification	http://eips.ethereum.org/EIPS/eip-55#Specification
Category	ERC

Abstract

In English, convert the address to hex, but if the ith digit is a letter (ie. it’s one of abcdef) print it in uppercase if the 4*ith bit of the hash of the lowercase hexadecimal address is 1 otherwise print it in lowercase.

Rationale

Benefit

Backwards compatible with many hex parsers that accept mixed case, allowing it to be easily introduced over timeKeeps the length at 40 charactersOn average there will be 15 check bits per address, and the net probability that a randomly generated address if mistyped will accidentally pass a check is 0.0247%. This is a ~50x improvement over ICAP, but not as good as a 4-byte check code.