Keychain 中存储的字符串有长度限制吗

在开发iOS应用程序时，我们经常需要在设备上存储一些敏感信息，例如用户的密码或者API密钥。为了保护这些信息不被恶意访问，苹果提供了一个安全的存储解决方案，称为Keychain。Keychain是一个加密的存储容器，可以用来安全地存储应用程序的敏感数据。

swift
import Security

swift
func saveToKeychain(service: String, key: String, value: String) -> Bool {
    guard let data = value.data(using: .utf8) else {
        return false
    }
    
    let query: [String: Any] = [
        kSecClass as String: kSecClassGenericPassword,
        kSecAttrService as String: service,
        kSecAttrAccount as String: key,
        kSecValueData as String: data
    ]
    
    let status = SecItemAdd(query as CFDictionary, nil)
    return status == errSecSuccess
}

swift
func retrieveFromKeychain(service: String, key: String) -> String? {
    let query: [String: Any] = [
        kSecClass as String: kSecClassGenericPassword,
        kSecAttrService as String: service,
        kSecAttrAccount as String: key,
        kSecReturnData as String: kCFBooleanTrue!,
        kSecMatchLimit as String: kSecMatchLimitOne
    ]
    
    var result: AnyObject?
    let status = SecItemCopyMatching(query as CFDictionary, &result)
    
    guard status == errSecSuccess,
          let data = result as? Data,
          let value = String(data: data, encoding: .utf8) else {
        return nil
    }
    
    return value
}

swift
let service = "com.example.app"
let key = "password"
let value = "secretpassword123"
// 存储字符串到Keychain中
let success = saveToKeychain(service: service, key: key, value: value)
if success {
    print("字符串成功存储到Keychain中")
} else {
    print("存储字符串到Keychain中失败")
}
// 从Keychain中检索字符串
if let retrievedValue = retrieveFromKeychain(service: service, key: key) {
    print("从Keychain中检索到的字符串为：\(retrievedValue)")
} else {
    print("无法从Keychain中检索到字符串")
}