Checksummed addresses

[stefanofornari]

AS A user
I WANT to see checksummed addressed
SO THAT I can use them more securely and prevent mistakes

see:

• https://ethereum.stackexchange.com/questions/2045/is-ethereum-wallet-address-case-sensitive
• Yet another cool checksum address encoding ethereum/EIPs#55 (comment)

For reference:

The checksum works like so:

    lowercase address and remove 0x prefix
    sha3 hash result from #1
    change nth letter of address according to the nth letter of the hash:

    0,1,2,3,4,5,6,7 → Lowercase
    8, 9, a, b, c, d, e, f → Uppercase

So, you sha3 hash the address, and look at each Nth character of the sha result. If it's 7 or below, the Nth character in the address is lowercase. If it is 8 or above, that character is uppercase.

(Brought from an old Ethereum forum whose [link is now broken](https://forum.ethereum.org/discussion/9220/eth-address-upper-and-lower-characters-does-not-matter).)