Capitalize an Ethereum address the EIP-55 way, or check the capitalization of one you were given. Each hex letter is uppercased when the matching nibble of keccak256(lowercase address) is 8 or more, which hides a checksum in the case — so 0xfb6916095ca1df60bb79ce92ce3ea74c37c5d359 becomes 0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359 .