blockchains-security-toolkit/basic_knowledge/cryptography/keccak.md

🥐 keccak

hashing

• hashing is a mathematical op converting an input message into a digest
• the transformation of a str of characters into a (usually shorter) fixed-length value or key that represents the original string.
• used to determine the integrity of a message, fast data retrieval and to encrypt/decrypt digital signatures
• collisions found: MD5 (128, 1992), SHA-1 (160, 1995)
• no collisions found: SHA-2 (224/256/384/512, 2001)

secure hash algorithm (SHA)

• family of cryptographic hash functions by NIST
• preprocessing: padding the data for blocking (fixed size message blocks)

SHA-3/keccak

• 2012 as the winner of the NIST hash function competition
• based on the sponge function: variable input and output length
• parameters (decides the strength):
  • r bits: rate, defines speed
  • c bits: capacity, defines the security level
• no key schedule, instead round constants
• state us 5x5x64 bits block
• the rho module rotates each 64-bit element by a triangular number: 0, 1, 3, 6, 10, 15...
• the pi module permutes the 64-bit elements
• the chi module adds a non-linear aspect to the permutation round
• the iota module breaks up any symmetry caused by the other modules, through XORing one of the array elements to a round constant

application & strength

• high level of parallelism
• flexibility, bit interleaving
• suited for protection against side-channel attack