cryptokit.shared.swift

let salt = "Salt".data(using: .utf8)!

let firstPrivateKey = P256.KeyAgreement.PrivateKey()
let firstPublicKey = firstPrivateKey.publicKey

let secondPrivateKey = P256.KeyAgreement.PrivateKey()
let secondPublicKey = secondPrivateKey.publicKey

let firstSharedSecret = try! firstPrivateKey.sharedSecretFromKeyAgreement(with: secondPublicKey)
let firstSymmetricKey = firstSharedSecret.hkdfDerivedSymmetricKey(using: SHA256.self,
                                                                  salt: salt,
                                                                  sharedInfo: Data(),
                                                                  outputByteCount: 32)

let secondSharedSecret = try! secondPrivateKey.sharedSecretFromKeyAgreement(with: firstPublicKey)

let secondSymmetricKey = secondSharedSecret.hkdfDerivedSymmetricKey(using: SHA256.self,
                                                              salt: salt,
                                                              sharedInfo: Data(),
                                                              outputByteCount: 32)

if firstSymmetricKey == secondSymmetricKey {
    print("First and second have the same key to do as they please")
}