According to the whitepaper, Blake3 can be used as a key derivation function (function key_derive). Currently, as a key derivation function, I used Rust's Hkdf::<Sha256> which takes as input the master key and salt. Adding salt allows to ensure that even in the case I reuse the master key, the output of the Hkdf is randomized and cannot be linked to previous derivations.
Since Blake3 is much faster than Sha256 I would like to use it as my KDF, however, according to the whitepaper Blake3 takes only a key material and context string, which should be " hardcoded, globally unique and application-specific (...) should not contain variable data like salts, IDs or current time".
How can I then add salt to Blake3 key derivation function, to ensure that even if I reuse the same master key multiple times, the output of the key derivation is randomized?
