CipherTools

Python BLAKE3 Hash Code Example (Online Runner)

Python BLAKE3 hashing examples with digest length control, keyed hashing, and context strings matching the online tool.

Online calculator: use the site BLAKE3 text tool.

Note: This snippet requires locally installed dependencies and will not run in the online runner.

Calculation method

BLAKE3 supports variable digest lengths, keyed hashing, and context-based derivation. The online tool exposes digest length, optional key, and optional context. Only one of key or context can be set at a time.

Python requires the blake3 package: pip install blake3.

Implementation notes

  • Package: blake3 implements the official BLAKE3 algorithm with keyed and context modes.
  • Implementation: BLAKE3 is an XOF, so digest_length controls output size in bytes. Keys must be exactly 32 bytes.
  • Notes: keyed mode is a MAC; context mode is for domain separation (derive_key_context) and cannot be combined with a key.
python
from typing import Optional
from blake3 import blake3

DEFAULT_DIGEST_LENGTH = 32
MAX_DIGEST_LENGTH = 64
KEY_LENGTH = 32


def blake3_text(
    text: str,
    digest_length: Optional[int] = None,
    key: Optional[str] = None,
    context: Optional[str] = None,
    encoding: str = "utf-8",
) -> str:
    if key and context:
        raise ValueError("Use either key or context, not both")
    digest_length = digest_length or DEFAULT_DIGEST_LENGTH
    if digest_length < 1 or digest_length > MAX_DIGEST_LENGTH:
        raise ValueError("Digest length must be between 1 and 64 bytes")
    key_bytes = key.encode(encoding) if key else None
    if key_bytes is not None and len(key_bytes) != KEY_LENGTH:
        raise ValueError("BLAKE3 keys must be exactly 32 bytes")

    hasher = blake3(text.encode(encoding), key=key_bytes, derive_key_context=context)
    return hasher.hexdigest(digest_length)

# Example usage
payload = "hello world"

print(blake3_text(payload))
print(blake3_text(payload, digest_length=16))
print(blake3_text(payload, key="k" * 32))
print(blake3_text(payload, context="my-app-v1"))

File hashing example

python
from pathlib import Path
import tempfile
from blake3 import blake3


def blake3_file(path: Path, digest_length: int = 32) -> str:
    hasher = blake3()
    with path.open("rb") as handle:
        for chunk in iter(lambda: handle.read(1024 * 1024), b""):
            hasher.update(chunk)
    return hasher.hexdigest(digest_length)


with tempfile.TemporaryDirectory() as temp_dir:
    sample_path = Path(temp_dir) / "example.bin"
    sample_path.write_bytes(b"example payload\n")
    print(blake3_file(sample_path))

Test vectors

InputExpected BLAKE3 (32-byte)
(empty string)af1349b9f5f9a1a6a0404dea36dcc9499bcb25c9adc112b7cc9a93cae41f3262

Complete script (implementation + tests)

python
from blake3 import blake3

TEST_VECTOR_EMPTY = "af1349b9f5f9a1a6a0404dea36dcc9499bcb25c9adc112b7cc9a93cae41f3262"


def blake3_text(text: str, digest_length: int = 32) -> str:
    hasher = blake3(text.encode("utf-8"))
    return hasher.hexdigest(digest_length)


def run_tests() -> None:
    assert blake3_text("") == TEST_VECTOR_EMPTY
    print("All BLAKE3 test vectors passed.")


if __name__ == "__main__":
    run_tests()