ethereum smart contract private value not safe

https://hackernoon.com/your-private-solidity-variable-is-not-private-save-it-before-it-becomes-public-52a723f29f5e


上面範例中，play(100)被呼叫後，從transcation data內得知

0x6587f6ec0000000000000000000000000000000000000000000000000000000000000064

然後先取得play()這部份的data

bytes4(keccak256('play(uint)'))

然後得知 0000000000000000000000000000000000000000000000000000000000000064 就是 uint部份，得到的這個值是經過hex才顯示的
byte32：00 為1個byte(16 bits)，共32個

64=> 6 * (16^1) + 4 * (16^0) = 100


uint256 => 2^256 => 8^32 => byte32