Question

我在使用钥匙串时遇到了最奇怪的问题。根据Realm的代码示例here，我有一个现有的应用程序正在使用加密的Realm数据库，并且加密密钥正在保存到钥匙串中。

- (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;
}

我正在将该应用程序转换为Swift，并且我正在尝试使用Realm的swift代码示例here

来检索存储在钥匙串中的加密密钥。

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: http://stackoverflow.com/questions/24145838/querying-ios-keychain-using-swift/27721328#27721328
    var dataTypeRef: AnyObject?
    var status = withUnsafeMutablePointer(to: &dataTypeRef) { SecItemCopyMatching(query as CFDictionary, UnsafeMutablePointer($0)) }
    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代码无法返回由Objective-C代码存储在钥匙串中的值。在创建keychainIdentifierData时，我曾尝试将Swift代码修改为使用NSData而不是Data，但是我无法使其正常工作。

在我的实际项目中，SecItemCopyMatching调用返回成功状态，但是dataTypeRef始终为nil，这在施于Data时强制崩溃。在为此创建的一个小型测试项目中，未找到密钥，这似乎表明问题出在将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保持一致。 / p>

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

哪个表示各语言的键不匹配，但是我不明白为什么SecItemCopyMatching返回成功。

有人对如何检索我的加密密钥有任何见识吗？在此先感谢:)

Answer 1

正在将Objective-C keychainIdentifier创建为C字符串，这些字符串始终以null终止。空终止符与会导致尾随的“ 00”的字符一起编码，并附加到结果中。 Swift字符串不以null终止。

要实现奇偶校验，请在创建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在Objective-C中表示您的标识符：

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

Answer 2

根据ncke的答案/评论创建答案

关键是像这样在我的Swift keychainIdentifierData的末尾添加了一个空终止符

keychainIdentifierData.append(0)

无法在Swift中检索在Objective-C中存储到钥匙串的值？

2 个答案: