Required Methods

fn new_from_context_key(context_key: &ContextKey) -> Self

Similar to Hasher::new_derive_key but using a pre-hashed ContextKey from hash_derive_key_context.

The hash_derive_key_context function is the only valid source of the ContextKey. Any other source (hash, keyed_hash, arbitrary bytes from the caller) violates the security requirements.

Calling derive_key or Hasher::new_derive_key in a loop will re-hash the context string every time. This constructor function is a performance optimization to avoid that repeated work. If you hardcode the ContextKey, the derive-key mode becomes zero-overhead, like the keyed mode.

Example

use blake3::Hasher;
use blake3::hazmat::HasherExt;

let context_key = blake3::hazmat::hash_derive_key_context("foo");
let mut hasher = Hasher::new_from_context_key(&context_key);
hasher.update(b"bar");
let derived_key = *hasher.finalize().as_bytes();

assert_eq!(derived_key, blake3::derive_key("foo", b"bar"));

fn set_input_offset(&mut self, offset: u64) -> &mut Self

Configure the Hasher to process a chunk or subtree starting at offset bytes into the whole input.

You must call this function before processing any input with update or similar. This step isn't required for the first chunk, or for a subtree that includes the first chunk (i.e. when the offset is zero), but it's required for all other chunks and subtrees.

The starting input offset of a subtree implies a maximum possible length for that subtree. See max_subtree_len and section 2.1 of the BLAKE3 paper. Note that only subtrees along the right edge of the whole tree can have a length less than their maximum possible length.

See the module level examples.

Panics

This function panics if the Hasher has already accepted any input with update or similar.

This should always be paired with finalize_non_root. It's never correct to use a non-zero input offset with finalize or finalize_xof. The offset must also be a multiple of CHUNK_LEN. Violating either of these rules will currently fail an assertion and panic, but this is not guaranteed.

fn finalize_non_root(&self) -> ChainingValue

Finalize the non-root hash ("chaining value") of the current chunk or subtree.

Afterwards you can merge subtree chaining values into parent nodes using merge_subtrees_non_root and ultimately into the root node with either merge_subtrees_root (similar to Hasher::finalize) or merge_subtrees_root_xof (similar to Hasher::finalize_xof).

See the module level examples, particularly the discussion of valid tree structures.