Blake-256

BLAKE-256 is a cryptographic hash function that takes input data of any length and produces a fixed 256-bit output, often called a digest or hash. It is the 256-bit member of the BLAKE family, designed in 2008 by Jean-Philippe Aumasson, Luca Henzen, Willi Meier and Raphael C.-W. Phan. BLAKE was one of five finalists in the US National Institute of Standards and Technology's competition to choose the SHA-3 standard, which was won by Keccak in 2012.

Although it did not become SHA-3, BLAKE was widely praised for its speed and security, and its successors BLAKE2 and BLAKE3 are used in many software products. In cryptocurrency, BLAKE-256 is best known as the basis of the proof-of-work algorithm of Decred, a network launched in 2016, while variants of BLAKE2 appear in several other projects. It is often compared with SHA-256, the hash function used in Bitcoin mining.

Imagine a machine that can take any document, from a single word to a whole library, and turn it into a short code of fixed length. The same document always gives the same code, but changing a single comma gives a completely different one. And there is no practical way to work backwards from the code to the document, or to find two documents that produce the same code.

BLAKE-256 is one of those machines. Computers use such codes to check that files have not been tampered with, to protect passwords, and in some blockchains to make miners do work: they keep feeding slightly different inputs into the machine until the code that comes out starts with enough zeros.

BLAKE-256 processes data in 512-bit blocks and keeps an internal state of 16 words of 32 bits each. Its design has several stages:

• Padding. The input is padded so that its length fits whole blocks, and its length is recorded to prevent certain attacks.
• Initialisation. The state is filled with fixed constants, the current chaining value and a counter of how many bits have been processed.
• Rounds. Each block is mixed through a series of rounds built from a function called G, which adds, rotates and XORs words of the state. The original BLAKE-256 used 14 rounds.
• Finalisation. After the last block, parts of the state are combined to produce the 256-bit output.

The G function is based on the ChaCha stream cipher designed by Daniel J. Bernstein, which is one reason BLAKE runs quickly on ordinary processors. The structure, known as HAIFA, includes the counter to make the hash resistant to some weaknesses found in older designs.

Decred, a cryptocurrency launched in February 2016, uses BLAKE-256 with 14 rounds for its proof-of-work mining, combined with a proof-of-stake voting system in a hybrid design discussed under hybrid PoW/PoS consensus. In 2023 Decred changed its mining algorithm to BLAKE3 to reduce the dominance of specialised mining hardware. Other projects have used BLAKE-based hashes: Siacoin adopted a BLAKE2b variant, and Zcash uses BLAKE2b inside its Equihash algorithm and elsewhere. As with SHA-256, popular BLAKE-based mining algorithms soon attracted ASIC miners, which perform the calculations much more efficiently than general computers and raise the hashrate of the network.

BLAKE2, released in 2012, simplified the original design and reduced the number of rounds, making it faster than MD5 and SHA-2 on many systems while remaining secure. It comes in two main versions, BLAKE2b for 64-bit platforms and BLAKE2s for smaller devices, and is used in password hashing, file integrity tools and secure messaging software. BLAKE3, released in 2020, goes further by arranging the computation as a tree, so that large inputs can be hashed in parallel across many processor cores. Both are free to use and widely implemented in open-source libraries.

No practical attack has broken full BLAKE-256 or its successors, and published cryptanalysis has only reached reduced-round versions. During the SHA-3 competition, NIST described BLAKE as having a large security margin. The choice between BLAKE and SHA-2 or SHA-3 often comes down to speed, hardware support and standards requirements: SHA-256 has dedicated instructions on many processors and is required in some regulated settings, while BLAKE2 and BLAKE3 are often faster in software. Hash functions underpin much of modern cryptography, including digital signatures, Merkle trees and salted password storage, so their strength matters well beyond mining.

For mining, the choice of hash function also shapes who can take part. A function that runs well on ordinary processors lets hobbyists join at first, but if the coin becomes valuable, manufacturers design dedicated chips for it, and the network's security then rests on a smaller group of industrial miners. Projects that value broad participation sometimes change algorithms to reset this process, as Decred did, though each change disrupts existing miners and can be controversial within the community.

• BLAKE2
• Decred