What is Keccak?

Keccak, standardized as SHA-3, is crucial in Ethereum's EVM for hashing transactions and smart contracts, ensuring blockchain security.

Apr 08, 2025 at 11:28 am

Keccak is a cryptographic hash function that was selected as the winner of the NIST hash function competition and subsequently standardized as SHA-3 (Secure Hash Algorithm 3). In the world of cryptocurrencies, Keccak plays a crucial role, particularly in the Ethereum blockchain, where it is used as the basis for the Ethereum Virtual Machine's (EVM) hash function. This article will delve into the details of Keccak, its significance in the cryptocurrency ecosystem, and how it is implemented in Ethereum.

The Origins and Development of Keccak

Keccak was designed by Guido Bertoni, Joan Daemen, Michaël Peeters, and Gilles Van Assche. The name "Keccak" is derived from the Ket language, spoken by the Ket people in Siberia. The algorithm was first introduced in 2008 and was submitted to the NIST competition in 2008. After rigorous testing and evaluation, Keccak was selected as the winner in 2012 and was standardized as SHA-3 in 2015.

The design of Keccak is based on the sponge construction, a novel approach to hash function design. The sponge construction allows for variable output lengths and is highly flexible, making it suitable for a wide range of cryptographic applications. This flexibility is one of the reasons why Keccak was chosen for use in Ethereum.

How Keccak Works

Keccak operates using a sponge function, which consists of two phases: the absorbing phase and the squeezing phase. During the absorbing phase, the input message is broken into fixed-size blocks and processed by the Keccak-f permutation function. The squeezing phase then extracts the desired output from the internal state of the sponge.

Here is a simplified overview of how Keccak processes data:

• Initialization: The internal state of the sponge is initialized to a fixed value.
• Absorbing Phase: The input message is padded and divided into blocks. Each block is XORed with the first part of the internal state, and then the entire state is processed by the Keccak-f permutation function.
• Squeezing Phase: After all blocks have been processed, the desired output is extracted from the internal state by repeatedly applying the Keccak-f permutation function and reading out parts of the state.

The Keccak-f permutation function is the core of the Keccak algorithm. It operates on a state array of 5x5 lanes, where each lane is a fixed number of bits (e.g., 64 bits for Keccak-f[1600]). The permutation function consists of five rounds of operations: theta, rho, pi, chi, and iota. These operations are designed to ensure that the output is highly unpredictable and resistant to various types of attacks.

Keccak in Ethereum

In the Ethereum blockchain, Keccak is used as the basis for the Ethereum Virtual Machine's (EVM) hash function, known as Keccak-256. This function is used for various purposes within the Ethereum ecosystem, including:

• Transaction Hashing: Each transaction in the Ethereum network is hashed using Keccak-256 to create a unique identifier.
• State Trie Hashing: The state of the Ethereum blockchain is stored in a trie data structure, and each node in the trie is hashed using Keccak-256.
• Smart Contract Execution: Keccak-256 is used within smart contracts to generate unique identifiers for events and to hash data.

The use of Keccak-256 in Ethereum ensures that the blockchain remains secure and resistant to various types of attacks. The cryptographic properties of Keccak, such as its resistance to collision attacks and preimage attacks, make it an ideal choice for securing the Ethereum network.

Implementing Keccak in Cryptocurrency Projects

For developers working on cryptocurrency projects, implementing Keccak can be a crucial step in ensuring the security of their systems. Here are some steps to implement Keccak in a cryptocurrency project:

• Choose the Right Library: There are several libraries available that implement Keccak, such as the Keccak Code Package and the SHA-3 library in OpenSSL. Choose a library that is well-maintained and widely used.

• Integrate the Library: Integrate the chosen library into your project. This typically involves adding the library to your project's dependencies and importing it into your code.

• Use the Keccak Function: Use the Keccak function provided by the library to hash your data. For example, in JavaScript using the keccak library, you can hash a string like this:

  const keccak256 = require('keccak256');
  const input = 'Hello, World!';
  const hash = keccak256(input);
  console.log(hash.toString('hex'));

• Test and Verify: Thoroughly test your implementation to ensure that it produces the correct output. You can use test vectors provided by the Keccak team to verify your implementation.

• Optimize for Performance: Depending on your project's requirements, you may need to optimize the performance of your Keccak implementation. This can involve using hardware acceleration or implementing the algorithm in a lower-level language like C or Rust.

Security Considerations with Keccak

While Keccak is considered to be a secure hash function, there are still some security considerations that developers should be aware of:

• Collision Resistance: Keccak is designed to be highly resistant to collision attacks, where two different inputs produce the same output hash. However, it is still important to use a sufficient output size (e.g., 256 bits) to minimize the risk of collisions.
• Preimage Resistance: Keccak is also designed to be resistant to preimage attacks, where an attacker tries to find an input that produces a specific output hash. However, it is important to use a sufficiently large input size to ensure that preimage attacks are infeasible.
• Side-Channel Attacks: Implementations of Keccak may be vulnerable to side-channel attacks, such as timing attacks or power analysis attacks. Developers should take care to implement Keccak in a way that minimizes the risk of side-channel attacks.

Keccak Variants and Their Uses

Keccak comes in several variants, each with different parameters and use cases. The most commonly used variants in the cryptocurrency space are:

• Keccak-224: This variant produces a 224-bit output and is used in some lightweight cryptographic applications.
• Keccak-256: This variant produces a 256-bit output and is the most commonly used variant in Ethereum and other cryptocurrency projects.
• Keccak-384: This variant produces a 384-bit output and is used in applications that require a higher level of security.
• Keccak-512: This variant produces a 512-bit output and is used in applications that require the highest level of security.

Each variant of Keccak is designed to provide a different balance between security and performance, allowing developers to choose the variant that best fits their specific needs.

Frequently Asked Questions

Q: How does Keccak differ from SHA-2?

A: Keccak and SHA-2 are both cryptographic hash functions, but they have different designs and properties. Keccak is based on the sponge construction, while SHA-2 is based on the Merkle–Damgård construction. Keccak is also designed to be more flexible and resistant to certain types of attacks, such as length extension attacks, which are a concern for SHA-2.

Q: Can Keccak be used for digital signatures?

A: Yes, Keccak can be used as part of a digital signature scheme. However, it is typically used in conjunction with other cryptographic primitives, such as elliptic curve cryptography, to create a complete digital signature algorithm.

Q: Is Keccak used in any other cryptocurrencies besides Ethereum?

A: Yes, Keccak is used in several other cryptocurrencies and blockchain projects. For example, the IOTA cryptocurrency uses a variant of Keccak called Curl-P, and the Zcash cryptocurrency uses Keccak as part of its Equihash proof-of-work algorithm.

Q: How can I verify the correctness of a Keccak implementation?

A: To verify the correctness of a Keccak implementation, you can use test vectors provided by the Keccak team. These test vectors are input-output pairs that can be used to check whether your implementation produces the correct output for a given input. You can find these test vectors on the official Keccak website.