What is the difference between Keychain and User Defaults?

UserDefaults is used for storing small, non-confidential data such as user settings or app state. Data is stored as key-value pairs in a .plist file and is accessible to all parts of the app. UserDefaults does not encrypt data and is not suitable for storing critical information.

Keychain is used for securely storing confidential data such as passwords, certificates, tokens, and other sensitive information. Data is encrypted and stored in a specialized storage accessible only to the app that saved it. Keychain is supported at the OS level and provides a high level of data protection.

Key differences:

Characteristic	UserDefaults	Keychain
Purpose	Storage of non-confidential settings	Storage of confidential data (passwords, tokens)
Security	No built-in encryption	Data is encrypted
Access	Accessible to all parts of the app	Accessible only to the app that saved it
Data volume	Suitable for small amounts of data	Suitable for small amounts of confidential data
Implementation	Simple API, stored in a .plist file	More complex API, stored in system storage

Example of using UserDefaults:

// Saving a value
UserDefaults.standard.set("dark", forKey: "theme")

// Retrieving a value
let theme = UserDefaults.standard.string(forKey: "theme")

Example of using Keychain (requires working with SecItem API or wrappers):

// Example of adding a password (simplified, requires error handling and additional parameters)
let password = "mySecretPassword".data(using: .utf8)!
let query: [String: Any] = [
    kSecClass as String: kSecClassGenericPassword,
    kSecAttrAccount as String: "myAccount",
    kSecValueData as String: password
]

let statusAdd = SecItemAdd(query as CFDictionary, nil)
// Handle status

// Example of retrieving a password (simplified, requires error handling)
let queryGet: [String: Any] = [
    kSecClass as String: kSecClassGenericPassword,
    kSecAttrAccount as String: "myAccount",
    kSecReturnData as String: kCFBooleanTrue!,
    kSecMatchLimit as String: kSecMatchLimitOne
]

var item: CFTypeRef?
let statusGet = SecItemCopyMatching(queryGet as CFDictionary, &item)

if statusGet == errSecSuccess {
    let retrievedData = item as! Data
    let retrievedPassword = String(data: retrievedData, encoding: .utf8)
    // Use the password
}