Objective-C 中存储到钥匙串的值无法在 Swift 中检索？

Question

我在钥匙串方面遇到了最奇怪的问题。我有一个现有的应用程序正在使用加密的 Realm 数据库，并且根据 Realm 的代码示例 here.

，加密密钥被保存到钥匙串中

- (NSData *)getKey {
    // Identifier for our keychain entry - should be unique for your application
    static const uint8_t kKeychainIdentifier[] = "io.Realm.EncryptionExampleKey";
    NSData *tag = [[NSData alloc] initWithBytesNoCopy:(void *)kKeychainIdentifier
                                               length:sizeof(kKeychainIdentifier)
                                         freeWhenDone:NO];

    // First check in the keychain for an existing key
    NSDictionary *query = @{(__bridge id)kSecClass: (__bridge id)kSecClassKey,
                            (__bridge id)kSecAttrApplicationTag: tag,
                            (__bridge id)kSecAttrKeySizeInBits: @512,
                            (__bridge id)kSecReturnData: @YES};

    CFTypeRef dataRef = NULL;
    OSStatus status = SecItemCopyMatching((__bridge CFDictionaryRef)query, &dataRef);
    if (status == errSecSuccess) {
        return (__bridge NSData *)dataRef;
    }

    // No pre-existing key from this application, so generate a new one
    uint8_t buffer[64];
    status = SecRandomCopyBytes(kSecRandomDefault, 64, buffer);
    NSAssert(status == 0, @"Failed to generate random bytes for key");
    NSData *keyData = [[NSData alloc] initWithBytes:buffer length:sizeof(buffer)];

    // Store the key in the keychain
    query = @{(__bridge id)kSecClass: (__bridge id)kSecClassKey,
              (__bridge id)kSecAttrApplicationTag: tag,
              (__bridge id)kSecAttrKeySizeInBits: @512,
              (__bridge id)kSecValueData: keyData};

    status = SecItemAdd((__bridge CFDictionaryRef)query, NULL);
    NSAssert(status == errSecSuccess, @"Failed to insert new key in the keychain");

    return keyData;
}

我正在努力将此应用程序转换为 Swift，并且我正在尝试使用 Realm 的 swift 代码示例 here[= 检索存储在钥匙串中的加密密钥18=]

func getKey() -> NSData {
    // Identifier for our keychain entry - should be unique for your application
    let keychainIdentifier = "io.Realm.EncryptionExampleKey"
    let keychainIdentifierData = keychainIdentifier.data(using: String.Encoding.utf8, allowLossyConversion: false)!

    // First check in the keychain for an existing key
    var query: [NSString: AnyObject] = [
        kSecClass: kSecClassKey,
        kSecAttrApplicationTag: keychainIdentifierData as AnyObject,
        kSecAttrKeySizeInBits: 512 as AnyObject,
        kSecReturnData: true as AnyObject
    ]

    // To avoid Swift optimization bug, should use withUnsafeMutablePointer() function to retrieve the keychain item
    // See also: 
    var dataTypeRef: AnyObject?
    var status = withUnsafeMutablePointer(to: &dataTypeRef) { SecItemCopyMatching(query as CFDictionary, UnsafeMutablePointer([=13=])) }
    if status == errSecSuccess {
        return dataTypeRef as! NSData
    }

    // No pre-existing key from this application, so generate a new one
    let keyData = NSMutableData(length: 64)!
    let result = SecRandomCopyBytes(kSecRandomDefault, 64, keyData.mutableBytes.bindMemory(to: UInt8.self, capacity: 64))
    assert(result == 0, "Failed to get random bytes")

    // Store the key in the keychain
    query = [
        kSecClass: kSecClassKey,
        kSecAttrApplicationTag: keychainIdentifierData as AnyObject,
        kSecAttrKeySizeInBits: 512 as AnyObject,
        kSecValueData: keyData
    ]

    status = SecItemAdd(query as CFDictionary, nil)
    assert(status == errSecSuccess, "Failed to insert the new key in the keychain")

    return keyData
}

现在的问题是 Swift 代码无法 return Objective-C 代码存储在钥匙串中的值。我尝试修改 Swift 代码以在创建 keychainIdentifierData 时使用 NSData 而不是数据，但我就是无法让它工作。

在我的实际项目中，SecItemCopyMatching 调用return是成功状态，但dataTypeRef 始终为nil，在强制转换为Data 时崩溃。在我为此创建的一个小测试项目中，找不到密钥，这似乎表明问题在于将 keychainIdentifier 转换为 keychainIdentifierData，但我现在找不到任何信息如何在不同语言之间一致地执行此操作。

我发现的一个线索是将 tag/keychainIdentifierData 打印到控制台，在 Obj-c 中是 <696f2e52 65616c6d 2e456e63 72797074 696f6e45 78616d70 6c654b65 7900>
在 Swift 中是
<696f2e52 65616c6d 2e456e63 72797074 696f6e45 78616d70 6c654b65 79>

这表明密钥在语言之间不匹配，但我不明白为什么 SecItemCopyMatching return 成功。

有人知道如何取回我的加密密钥吗？提前致谢:)

Answer 1

Objective-C keychainIdentifier 被创建为 C 字符串，它始终以 null 结尾。空终止符与导致您注意到的尾随“00”附加到结果的字符一起编码。 Swift 字符串不是空终止的。

为了实现奇偶校验，在创建 Objective-C 标识符时省略最后一个字符：

static const uint8_t kKeychainIdentifier[] = "io.Realm.EncryptionExampleKey";
NSData *tag = [[NSData alloc] initWithBytesNoCopy:(void *)kKeychainIdentifier
                                           length:sizeof(kKeychainIdentifier) - 1 // <- Truncate last char
                                     freeWhenDone:NO];

或者，使用 NSString 表示您在 Objective-C 中的标识符：

NSString *keychainIdentifier = @"io.Realm.EncryptionExampleKey";
NSData *tag = [keychainIdentifier dataUsingEncoding:NSUTF8StringEncoding];

Answer 2

根据 ncke 的 answer/comment 创建一个答案：

密钥在我的 Swift keychainIdentifierData 的末尾附加了一个空终止符，就像这样

keychainIdentifierData.append(0)

Objective-C 中存储到钥匙串的值无法在 Swift 中检索？

Value stored to Keychain in Objective-C can't be retrieved in Swift?

objective-c

keychain

ios

swift