Быстрое шифрование с использованием Security framework

Я пытался быстро зашифровать и расшифровать строку, используя обмен ключами Диффи Хеллмана и шифрование по эллиптической кривой. Но после обмена ключами я не могу восстановить закрытый ключ из переменной CFData shared1 / shared2 для дешифрования. Все, что я получаю, - это нулевое значение.

let attributes: [String: Any] = [kSecAttrKeySizeInBits as String: 256,
                                     kSecAttrKeyType as String: kSecAttrKeyTypeEC,
                                     kSecPrivateKeyAttrs as String: [kSecAttrIsPermanent as String: false]]
    var error: Unmanaged<CFError>?
    if #available(iOS 10.0, *) {
        guard let privateKey1 = SecKeyCreateRandomKey(attributes as CFDictionary, &error) else {return}

        let publicKey1 = SecKeyCopyPublicKey(privateKey1)
        guard let privateKey2 = SecKeyCreateRandomKey(attributes as CFDictionary, &error) else {return}

        let publicKey2 = SecKeyCopyPublicKey(privateKey2)

        let dict: [String: Any] = [:]

        guard let shared1 = SecKeyCopyKeyExchangeResult(privateKey1, SecKeyAlgorithm.ecdhKeyExchangeStandardX963SHA256, publicKey2!, dict as CFDictionary, &error) else {return}

        guard let shared2 = SecKeyCopyKeyExchangeResult(privateKey2, SecKeyAlgorithm.ecdhKeyExchangeStandardX963SHA256, publicKey1!, dict as CFDictionary, &error) else {return}

        print(shared1==shared2)
        let options: [String: Any] = [kSecAttrKeyType as String: kSecAttrKeyTypeEC,
                                      kSecAttrKeyClass as String: kSecAttrKeyClassPrivate,
                                      kSecAttrKeySizeInBits as String : 256]

        guard let key = SecKeyCreateWithData(shared1 as CFData,
                                             options as CFDictionary,
                                             &error) else {return}
        print(key)


        let str = "Hello"
        let byteStr: [UInt8] = Array(str.utf8)
        let cfData = CFDataCreate(nil, byteStr, byteStr.count)


        guard let encrypted = SecKeyCreateEncryptedData(publicKey1!,
                                                        SecKeyAlgorithm.eciesEncryptionStandardX963SHA256AESGCM,
                                                        cfData!,
                                                        &error) else {return}

        guard let decrypted = SecKeyCreateDecryptedData(key,
                                                        SecKeyAlgorithm.eciesEncryptionStandardX963SHA256AESGCM,
                                                        encrypted,
                                                        &error) else {return}




        print(decrypted)

    } else {
        print("unsupported")
    }