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Jack O'Connor
This will let us add big endian testing to CI for our C code. (We were
already doing it for our Rust code.)

This is adapted from test_vectors/ It works around the
limitation that the `cross` tool can't reach parent directories. It's an
unfortunate hack, but at least it's only for testing. It might've been
less hacky to use symlinks for this somehow, but I worry that would
break things on Windows, and I don't want to have to add workarounds for
my workarounds.

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BLAKE3 is a cryptographic hash function that is:

  • Much faster than MD5, SHA-1, SHA-2, SHA-3, and BLAKE2.
  • Secure, unlike MD5 and SHA-1. And secure against length extension, unlike SHA-2.
  • Highly parallelizable across any number of threads and SIMD lanes, because it's a Merkle tree on the inside.
  • Capable of verified streaming and incremental updates, again because it's a Merkle tree.
  • A PRF, MAC, KDF, and XOF, as well as a regular hash.
  • One algorithm with no variants, which is fast on x86-64 and also on smaller architectures.

The chart below is an example benchmark of 16 KiB inputs on modern server hardware (a Cascade Lake-SP 8275CL processor). For more detailed benchmarks, see the BLAKE3 paper.

performance graph

BLAKE3 is based on an optimized instance of the established hash function BLAKE2 and on the original Bao tree mode. The specifications and design rationale are available in the BLAKE3 paper. The default output size is 256 bits. The current version of Bao implements verified streaming with BLAKE3.

This repository is the official implementation of BLAKE3. It includes:

  • The blake3 Rust crate, which includes optimized implementations for SSE2, SSE4.1, AVX2, AVX-512, and NEON, with automatic runtime CPU feature detection on x86. The rayon feature provides multithreading.

  • The b3sum Rust crate, which provides a command line interface. It uses multithreading by default, making it an order of magnitude faster than e.g. sha256sum on typical desktop hardware.

  • The C implementation, which like the Rust implementation includes SIMD code and runtime CPU feature detection on x86. Unlike the Rust implementation, it's not currently multithreaded. See c/

  • The reference implementation, which is discussed in Section 5.1 of the BLAKE3 paper. This implementation is much smaller and simpler than the optimized ones above. If you want to see how BLAKE3 works, or you're writing a port that doesn't need multithreading or SIMD optimizations, start here.

  • A set of test vectors that covers extended outputs, all three modes, and a variety of input lengths.

  • Actions Status

BLAKE3 was designed by:

The development of BLAKE3 was sponsored by Teserakt and Electric Coin Company.

NOTE: BLAKE3 is not a password hashing algorithm, because it's designed to be fast, whereas password hashing should not be fast. If you hash passwords to store the hashes or if you derive keys from passwords, we recommend Argon2.


The b3sum utility

The b3sum command line utility prints the BLAKE3 hashes of files or of standard input. Prebuilt binaries are available for Linux, Windows, and macOS (requiring the unidentified developer workaround) on the releases page. If you've installed Rust and Cargo, you can also build b3sum yourself with:

cargo install b3sum

If rustup didn't configure your PATH for you, you might need to go looking for the installed binary in e.g. ~/.cargo/bin. You can test out how fast BLAKE3 is on your machine by creating a big file and hashing it, for example:

# Create a 1 GB file.
head -c 1000000000 /dev/zero > /tmp/bigfile
# Hash it with SHA-256.
time openssl sha256 /tmp/bigfile
# Hash it with BLAKE3.
time b3sum /tmp/bigfile

The blake3 crate

To use BLAKE3 from Rust code, add a dependency on the blake3 crate to your Cargo.toml. Here's an example of hashing some input bytes:

// Hash an input all at once.
let hash1 = blake3::hash(b"foobarbaz");

// Hash an input incrementally.
let mut hasher = blake3::Hasher::new();
let hash2 = hasher.finalize();
assert_eq!(hash1, hash2);

// Extended output. OutputReader also implements Read and Seek.
let mut output = [0; 1000];
let mut output_reader = hasher.finalize_xof();
output_reader.fill(&mut output);
assert_eq!(&output[..32], hash1.as_bytes());

// Print a hash as hex.
println!("{}", hash1.to_hex());

Besides hash, BLAKE3 provides two other modes, keyed_hash and derive_key. The keyed_hash mode takes a 256-bit key:

// MAC an input all at once.
let example_key = [42u8; 32];
let mac1 = blake3::keyed_hash(&example_key, b"example input");

// MAC incrementally.
let mut hasher = blake3::Hasher::new_keyed(&example_key);
hasher.update(b"example input");
let mac2 = hasher.finalize();
assert_eq!(mac1, mac2);

The derive_key mode takes a context string of any length and key material of any length, and it outputs a derived key of any length. The context string should be hardcoded, globally unique, and application-specific. A good default format for the context string is "[application] [commit timestamp] [purpose]":

// Derive a couple of subkeys for different purposes.
const EMAIL_CONTEXT: &str = "BLAKE3 example 2020-01-07 17:10:44 email key";
const API_CONTEXT: &str = "BLAKE3 example 2020-01-07 17:11:21 API key";
let input_key = b"some very secret key material (>'-')> <('-'<) ^('-')^";
let mut email_key = [0; 32];
blake3::derive_key(EMAIL_CONTEXT, input_key, &mut email_key);
let mut api_key = [0; 32];
blake3::derive_key(API_CONTEXT, input_key, &mut api_key);
assert!(email_key != api_key);

The C implementation

See c/

Other implementations

We post links to third-party bindings and implementations on the @BLAKE3team Twitter account whenever we hear about them. Some highlights include an optimized Go implementation, Wasm bindings for Node.js and browsers, and binary wheels for Python.


Please see

Intellectual property

The Rust code is copyright Jack O'Connor, 2019-2020. The C code is copyright Samuel Neves and Jack O'Connor, 2019-2020. The assembly code is copyright Samuel Neves, 2019-2020.

This work is released into the public domain with CC0 1.0. Alternatively, it is licensed under the Apache License 2.0.


the official Rust and C implementations of the BLAKE3 cryptographic hash function




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