ecies 0.2.11

Elliptic Curve Integrated Encryption Scheme for secp256k1
Documentation 
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use hkdf::Hkdf;
use sha2::Sha256;

use crate::compat::Vec;
use crate::consts::{SharedSecret, EMPTY_BYTES, ZERO_SECRET};

pub fn hkdf_derive(part1: &[u8], part2: &[u8]) -> SharedSecret {
    let size = part1.len() + part2.len();
    let mut master = Vec::with_capacity(size);
    master.extend(part1);
    master.extend(part2);
    hkdf_sha256(&master)
}

fn hkdf_sha256(master: &[u8]) -> SharedSecret {
    let h = Hkdf::<Sha256>::new(None, master);
    let mut out = ZERO_SECRET;
    // never fails because 32 < 255 * chunk_len, which is 32 on SHA256
    h.expand(&EMPTY_BYTES, &mut out).unwrap();
    out
}

#[cfg(test)]
mod tests {
    use super::hkdf_sha256;

    use crate::utils::tests::decode_hex;

    #[test]
    fn test_known_vector() {
        assert_eq!(
            hkdf_sha256(b"secret").to_vec(),
            decode_hex("2f34e5ff91ec85d53ca9b543683174d0cf550b60d5f52b24c97b386cfcf6cbbf")
        );
    }
}