如何在钥匙链中保存 NSString 公钥，然后获取它的 SecKeyRef？

Question

我有一个NSString，它应该是公钥。我想将它存储在钥匙串中，然后获取它的 SecKeyRef ，以便在其他安全相关函数中使用它，例如 SecKeyEncrypt 等。

为了存储，我使用SecItemAdd 假设我还有公钥的标识符。我尝试获取持久引用，然后通过此获取带有 SecItemCopyMatching 的 SecKeyRef 。我使用以下两个函数。在将密钥字符串传递给 putKey 之前，我将其转换为 NSData。

-(SecKeyRef)putKey:(NSData *)key withIdentifier:(NSString *)identifier 
{
    OSStatus status = noErr;
    SecKeyRef keyRef = nil;
    CFTypeRef persKey = nil;

    NSData * identifierTag = [[NSData alloc] initWithBytes:(const void *)[identifier UTF8String] length:[identifier length]];
    NSMutableDictionary *queryKey = [[NSMutableDictionary alloc] init];

    [queryKey setObject:(__bridge id)kSecClassKey forKey:(__bridge id)kSecClass];
    [queryKey setObject:(__bridge id)kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];
    [queryKey setObject:identifierTag forKey:(__bridge id)kSecAttrApplicationTag];
    [queryKey setObject:key forKey:(__bridge id)kSecValueData];
    [queryKey setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecReturnPersistentRef];

    status = SecItemAdd((__bridge CFDictionaryRef)queryKey, (CFTypeRef *)&persKey);

    if (status == errSecDuplicateItem) NSLog(@"Key %@ already exists in the KeyStore, OSStatus = %ld.", identifier, status);
    else if (status != noErr) NSLog(@"Error putting key %@ in KeyStore, OSStatus = %ld.", identifier, status);

    keyRef = [self getKeyRefWithPersistentKeyRef:persKey];

    return keyRef;
}

- (SecKeyRef)getKeyRefWithPersistentKeyRef:(CFTypeRef)persistentRef
{
    OSStatus sanityCheck = noErr;
    SecKeyRef keyRef = NULL;

    if (persistentRef == NULL) NSLog(@"persistentRef object cannot be NULL.");

    NSMutableDictionary * queryKey = [[NSMutableDictionary alloc] init];

    // Set the SecKeyRef query dictionary.
    [queryKey setObject:(__bridge id)persistentRef forKey:(__bridge id)kSecValuePersistentRef];
    [queryKey setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecReturnRef];

    // Get the key reference.
    sanityCheck = SecItemCopyMatching((__bridge CFDictionaryRef)queryKey, (CFTypeRef *)&keyRef);

    return keyRef;
 }

SecItemAdd 成功返回持久密钥引用。

But SecItemCopyMatching returns 0x0. Anyone knows why?

Answer 1

查看 Apple 的加密练习。为了将公钥添加到 KeyChain，需要去掉附加的标头。 Apple 的示例表明就是这样做的，并且代码很容易重用。