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I was testing the hash value of null values for different types and I'm curious how it generates different results for different types. Here are the results. 

String = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470
Address = 0x5380c7b7ae81a58eb98d9c78de4a1fd7fd9535fc953ed2be602daaa41767312a
Bytes = 0x290decd9548b62a8d60345a988386fc84ba6bc95484008f6362f93160ef3e563
Uint = 0x290decd9548b62a8d60345a988386fc84ba6bc95484008f6362f93160ef3e563
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The results are for hashing different numbers of zero bytes:

  • keccak256('') is the hash of 0 zero bytes.

  • keccak256(address(0)) is the hash of 20 zero bytes

  • keccak256(uint(0)) is the hash of 32 zero bytes (same for bytes32 type)

The way keccak pads the input accounts for the different outputs.

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  • Oh ok thanks. So the input is converted to bytes and then hashed?
    – arete
    Commented Jan 4, 2018 at 13:41
  • You could look at it like that... but everything is already just bytes under the hood, so no conversion necessary. An address is just a block of 20 bytes.
    – benjaminion
    Commented Jan 4, 2018 at 15:35

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