Specification

Code:

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

Benefits:

• Backwards compatible with many hex parsers that accept mixed case, allowing it to be easily introduced over time
• Keeps the length at 40 characters
• On 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.

Implementation

In javascript:

Note that the input to the Keccak256 hash is the lowercase hexadecimal string (i.e. the hex address encoded as ASCII):

Test Cases