要保存和读取SecKey到Keychain，可以按照以下步骤进行操作：

1. 首先，定义一个函数来保存SecKey到Keychain：

func saveKeyToKeychain(key: SecKey, keyLabel: String) -> Bool {
    let query: [String: Any] = [
        kSecClass as String: kSecClassKey,
        kSecAttrApplicationTag as String: keyLabel,
        kSecValueRef as String: key
    ]
    
    let status = SecItemAdd(query as CFDictionary, nil)
    return status == errSecSuccess
}

2. 接下来，定义一个函数来从Keychain读取SecKey：

func loadKeyFromKeychain(keyLabel: String) -> SecKey? {
    let query: [String: Any] = [
        kSecClass as String: kSecClassKey,
        kSecAttrApplicationTag as String: keyLabel,
        kSecReturnRef as String: kCFBooleanTrue
    ]
    
    var keyRef: CFTypeRef?
    let status = SecItemCopyMatching(query as CFDictionary, &keyRef)
    
    if status == errSecSuccess {
        return (keyRef as! SecKey)
    }
    
    return nil
}

3. 最后，可以使用上述函数进行保存和读取SecKey。例如：

// 生成一个RSA密钥对
let privateKey = generatePrivateKey()
let publicKey = SecKeyCopyPublicKey(privateKey)!

// 保存私钥到Keychain
saveKeyToKeychain(key: privateKey, keyLabel: "PrivateKeyLabel")

// 从Keychain读取私钥
let loadedPrivateKey = loadKeyFromKeychain(keyLabel: "PrivateKeyLabel")

上述代码示例中，generatePrivateKey()函数用于生成一个RSA私钥，SecKeyCopyPublicKey()函数用于从私钥中获取公钥。

请注意，保存和读取SecKey到Keychain需要在应用的Keychain访问权限配置中进行相应的设置。在Xcode中，可以在项目的Capabilities选项卡中打开Keychain Sharing并添加相应的Keychain组件。