BLAKE3

BLAKE3: 32-byte digests, faster than SHA-256 in hardware without SHA instructions, and the hash the compiler’s build cache keys objects with. Also a keyed hash (a MAC), key derivation, and output of any length.

Source: runtime/digest/blake3.pep

Blake3

struct Blake3

An incremental BLAKE3 hasher: feed it bytes with update, any number of times and in pieces of any size, then read the 32-byte digest with finish.

Blake3() is the default hash mode; Blake3.keyed and Blake3.derive_key make hashers for the other two modes, and finish(length) reads output of any length in each.

This is a portable implementation, one block at a time; it does not use SIMD or threads, so it runs well below the speed of the official C and Rust implementations. The digests are the same. finish resets the hasher, so it can hash a new input.

Example

import digest;

var hasher = digest.Blake3();
hasher.update("hello ");
hasher.update("world");
assert(hasher.finish_hex() == digest.to_hex(digest.blake3("hello world")), "same digest");

Constructor

Blake3()

construct()

Creates a hasher in the initial state, with no input.

Static methods

keyed

static keyed(key: u8[]): Blake3

Returns a hasher for BLAKE3’s keyed mode, a MAC: only someone with key can compute or check the digest of an input.

Parameters

• key — the 32-byte secret key

Returns

• a hasher with no input, keyed with key

Panics

• if key is not 32 bytes

Example

import digest;

var key = digest.blake3("a key made some other way");
var mac = digest.Blake3.keyed(key);
mac.update("message");
assert(mac.finish().count == 32, "a 32-byte MAC");

derive_key

static derive_key(context: String): Blake3

Returns a hasher for BLAKE3’s key derivation mode: the digest of its input (the key material, such as a shared secret or a password hash) is a key for the purpose that context names.

context should be a hard-coded string, unique to the application and the purpose, such as "example.com 2026-10-16 session tokens v1"; different contexts give unrelated keys from the same material. Read the key with finish, or finish(length) for one of another length.

Parameters

• context — the application and purpose the key is for

Returns

• a hasher with no input, for keys in context

Example

import digest;

var hasher = digest.Blake3.derive_key("example.com 2026-10-16 session tokens v1");
hasher.update("the shared secret");
var key = hasher.finish();

Methods

reset

reset()

Discards the input given so far, returning the hasher to its initial state.

update

update(bytes: u8[])

Hashes bytes as the next part of the input.

Parameters

• bytes — the bytes to add

update_range

update_range(bytes: u8[], start: ulong, count: ulong)

Hashes count bytes of bytes, from index start, as the next part of the input; those past the end of bytes are left out.

Parameters

• bytes — the bytes
• start — the index of the first byte to add
• count — how many bytes to add

update

update(text: String)

Hashes the UTF-8 bytes of text (without a terminating NUL) as the next part of the input.

Parameters

• text — the text to add

finish

finish(): u8[]

Returns the 32-byte digest of the input given since the hasher was created or last reset, then resets it.

Returns

• the digest

finish

finish(length: ulong): u8[]

Returns length bytes of output for the input given since the hasher was created or last reset, then resets it: BLAKE3’s extended output. The first 32 bytes are the digest finish() returns, and a shorter output is a prefix of a longer one.

Parameters

• length — how many bytes to return

Returns

• the output

Example

import digest;

var long_output = digest.Blake3();
long_output.update("abc");
var bytes = long_output.finish(100);
assert(digest.to_hex(bytes).starts_with(digest.to_hex(digest.blake3("abc"))), "a prefix");

finish_hex

finish_hex(): String

Returns the digest as finish does, written as 64 lowercase hexadecimal digits.

Returns

• the digest in hexadecimal

blake3

blake3(bytes: u8[]): u8[]

Returns the BLAKE3 digest of bytes.

Parameters

• bytes — the input

Returns

• the 32-byte digest

Example

import digest;

var empty = "af1349b9f5f9a1a6a0404dea36dcc9499bcb25c9adc112b7cc9a93cae41f3262";
assert(digest.to_hex(digest.blake3(Array<u8>())) == empty, "BLAKE3 of nothing");

blake3

blake3(text: String): u8[]

Returns the BLAKE3 digest of the UTF-8 bytes of text.

Parameters

• text — the input

Returns

• the 32-byte digest