Function derive_key 

pub fn derive_key<H: Hasher, const N: usize>(
    ikm: &[u8],
    info: &[u8],
    salt: Option<&[u8]>,
) -> Result<[u8; N], HkdfError>

One-shot HKDF: extract-then-expand in a single call.

Example

use crypto::hkdf;
use crypto::sha2::Sha256;

let okm: [u8; 32] = hkdf::derive_key::<Sha256, 32>(
    b"input key material",
    b"context info",
    Some(b"salt"),
).unwrap();

Error

Returns an error if N > 255 * H::OUTPUT_SIZE.