Keccak secure hash

This module implements the interface to Keccak secure hash functions. There is a lot of confusion about the relation between Keccak hash functions and SHA3 hash functions. The NIST organized a contest to develop the next standard secure hash function to use in place of SHA2. The Keccak team won the competition with its reference implementation known as Keccak secure hash. However the NIST changed the Keccak implementation before making it a standard known as SHA3 in 2015. The standard SHA3, described in FIPS202 is therefore different from the original Keccak (by the value of the padding bytes). Even if SHA3 is now the standard, Keccak hash is still important because, since the contest lasted from 2008 to 2015, in that time many software projects recognized the enhanced security of Keccak and included the original implementation before the standard was published. One of such project is the blockchain Ethereum . Sadly, both Keccak and official SHA3 are often simply called SHA3, arising much confusion. One simple way to test an implementation of a SHA3 algorithm is to generate the hash of the empty string:

  • c5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is the original Keccak-256
  • a7ffc6f8bf1ed76651c14756a061d662f580ff4de43b49fa82d80a4b80f8434a is the NIST SHA3-256

The module is used in the same way as all crypto hash modules: an instance of the Keccak class is created, then feed this object with arbitrary strings/bytes using the update() method, and at any point you can ask it for the digest of the concatenation of the strings fed to it so far.

The class supports 4 variants of Keccak, selectable in the constructor with one of the following constants:

  • KECCAK224
  • KECCAK256
  • KECCAK284
  • KECCAK512

The module is based on a patched version of the C library cifra.

The Keccak class

class Keccak(hashtype=KECCAK256)

This class allows the generation of Keccak hashes. It is thread safe. By default, it calculates the Keccak-256 variant. This behaviour can be changed by passing a different value for hashtype


Update the sha object with the string data. Repeated calls are equivalent to a single call with the concatenation of all the arguments: m.update(a); m.update(b) is equivalent to m.update(a+b).


Return the digest of the strings passed to the update method so far. This is a byte object with length depending on the Keccak variant.


Like digest except the digest is returned as a string containing only hexadecimal digits.