SquarePants Sponge Hashing
In 2007, the NIST (National Institue of Standards and Technology) announced a Cryptographic Hash Algorithm Competition, with the winner being awarded the grant to be standardized as the new SHA-3. It ended in 2012 with 
being announced as the winner.
The function uses a sponge construction, but what the hell is even this thing? Let's take a look!
We have a message 
as our input and the final hash 
. We then have two "registers": 
and 
, which both make up our state 
. These two are initialized with 
s in them.
The message is first padded so that it can fit in exactly 
parts 
, each of size . The process of "absorption" is the following:
- XOR (denoted
) the message-part with the register bit-by-bit - Scramble the whole register ( and ) altogether to produce a new state
by applying 
The function needs to generate a pseudo-random permutation of the bits in
Example permutation via f
- Pass on the state to the next iteration
We can now "squeeze" our sponge to extract the hash from it, by applying again and taking a small chunk 
( bits) over and over until we have enough for our desired output length.
This whole process can be described with the following diagram:
Sponge construction algorithm, inspired by Keccak's diagram
This whole process can also be modified to fit streaming needs, by combining both absorption and squeezing steps at each iteration.
