I changed the bundle ID then it works...I doubt if it is because the previous bundle ID is too long.

Thanks so much. I wrote the below two methods to create and read keys. Another small question - is it possible to store/get the specific creation time of the key generated when reading the key from the keychain? internal func generateAndStoreSymmetricKey(withKeychainTag: String) throws {   // Parameter:   let alias = withKeychainTag       let key = SymmetricKey(size: .bits256)       let addQuery:[CFString:Any] = [     kSecClass: kSecClassGenericPassword,     kSecAttrLabel: alias,     kSecAttrAccount: "Account \(alias)",     kSecAttrService: "Service \(alias)",     kSecReturnAttributes: true,     kSecValueData: key.rawRepresentation   ]       var result: CFTypeRef?   let status = SecItemAdd(addQuery as CFDictionary, &result)   guard status == errSecSuccess else {     throw Error.client("Failed to insert symmetric key into keychain: \(withKeychainTag)")   } } internal func retrieveSymmetricKey(withKeychainTag: String) throws -> SymmetricKey? {   // Parameter:   let alias = withKeychainTag       // Seek a generic password with the given account.   let query = [kSecClass: kSecClassGenericPassword,          kSecAttrAccount: "Account \(alias)",          kSecUseDataProtectionKeychain: true,          kSecReturnData: true] as [String: Any]   // Find and cast the result as data.   var item: CFTypeRef?   switch SecItemCopyMatching(query as CFDictionary, &item) {   case errSecSuccess:     guard let data = item as? Data else { throw Error.client("Fail to convert the key reference to Data.") }     return try SymmetricKey(rawRepresentation: data) // Convert back to a key.   case errSecItemNotFound: return nil   default: throw Error("Error in reading the key")   } }

Thanks for answering! Based on our guideline, we are supposed to use AES-CBC for encryption. And I generated a random 256-bits symmetric key to achieve this. (Please find the code snippets below.) I have a question here - how can I store such a symmetric key into keychain? Thanks! internal func generateSymmetricEncryptionKey() throws -> String {     var keyData = Data(count: 32)     let result = keyData.withUnsafeMutableBytes {       SecRandomCopyBytes(kSecRandomDefault, 32, $0.baseAddress!)     }           guard result == errSecSuccess else {       throw error     }     return keyData.base64EncodedString()   }