忽略共享特性时，Keychain与NSSecureCoding存储安全性是否等同？

Great question! Let's break this down clearly, since it's easy to mix up what these two technologies actually do:

Short answer: No—they solve different problems, and Keychain provides far stronger storage security out of the box, even without cross-app sharing.

Let’s break down the key distinctions:

1. What Each Technology Actually Does #

• NSSecureCoding is first and foremost a safe serialization/deserialization protocol. Its only job is to prevent security issues during the process of converting objects to data (archiving) and back (unarchiving). For example, it blocks maliciously crafted archive data from triggering type confusion attacks (a flaw in the older NSCoding protocol that let attackers replace expected object types with dangerous alternatives). It does not handle encryption, storage location, or access control for the data it produces.

  Your User class implementing NSSecureCoding (like the snippet you shared):

  class User: NSObject, NSSecureCoding { 
    private enum CodingKeys: String, CodingKey { /* ... */ }
    // ... NSSecureCoding implementation ...
  }
  

  This just ensures that when you unarchive a User from data, you won’t get unexpected (and potentially dangerous) object types. It says nothing about how that data is stored or protected once written to disk.

• Keychain is a system-level secure storage container. It’s designed specifically to store sensitive data (passwords, tokens, keys) with built-in protections:

  • Automatic encryption using device hardware (like the Secure Enclave on iOS/macOS)
  • Granular access control rules (e.g., only allow access when the device is unlocked, or require Touch ID/Face ID)
  • Tamper detection (data modified outside the system’s control becomes unreadable)
  • Isolation from other apps and system processes (even with cross-app sharing disabled)

2. Security Gap When Using NSSecureCoding Alone #

If you take the data produced by NSSecureCoding and save it to a standard file (like in the Documents or Library directory), that data is:

• Stored as plaintext unless you manually encrypt it
• Vulnerable to unauthorized access if the device is jailbroken or the file system is mounted externally
• Lacking any built-in tamper protection (an attacker could modify the file, and your app might unarchive corrupted or malicious data)

To get even close to Keychain’s security with NSSecureCoding, you’d have to:

1. Implement strong encryption (AES-256, for example) on the serialized data
2. Securely store the encryption key (which usually means storing it in... wait, the Keychain!)
3. Add your own tamper detection (like HMAC checks)
4. Manage access control for the file (which is far less robust than Keychain’s system-level rules)

This is a lot of work—and even then, you’re unlikely to match the rigor of Apple’s built-in Keychain implementation.

3. Even Without Cross-App Sharing, Keychain Has Unique Security Benefits #

Ignoring cross-app sharing, Keychain still provides critical protections that NSSecureCoding can’t:

• System-managed encryption: You don’t have to write or maintain encryption code—Apple handles it, including updates for new security threats.
• Hardware-backed security: On modern devices, Keychain uses the Secure Enclave to store sensitive data, which is isolated from the main processor and impossible to extract even if the device is compromised.
• Built-in access controls: You can restrict Keychain items to only be accessible when the device is unlocked, or require biometric authentication—something you can’t do with a standard file, even if you encrypt it.

NSSecureCoding is a tool to make object serialization safe, not a secure storage solution. Keychain is a purpose-built secure storage system with system-level protections that go far beyond what NSSecureCoding provides, even when you ignore its cross-app sharing feature.

If your goal is to store sensitive user data securely, Keychain is the right choice. NSSecureCoding complements it (e.g., if you need to serialize a complex object before storing it in Keychain), but it can’t replace Keychain’s storage security.

内容的提问来源于stack exchange，提问作者Congruent Tech. UG