Pure Rust implementation of the Concatenation Key Derivation Function (Concat KDF) generic over hash function. This function is described in the section 5.8.1 of NIST SP 800-56A, Recommendation for Pair-Wise Key Establishment Schemes Using Discrete Logarithm Cryptography.
The most common way to use Concat KDF is as follows: you generate a shared secret with other party (e.g. via Diffie-Hellman algorithm) and use key derivation function to derive a shared key.
let mut key = [0u8; 32];
concat_kdf::derive_key_into::<sha2::Sha256>(b"shared-secret", b"other-info", &mut key).unwrap();