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我在将对称密钥从 SecKeyRef 导出到 CFDataRef 以进行包装或存储或仅与其他 Cocoa 代码一起使用时遇到了一些麻烦。

我有以下代码：

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    SecKeyRef sessionKey = [self generateRandomSymmetricKey];
    CFDataRef sessionKeyData = [self exportSymmetricKeyAsCFData:sessionKey];
}

- (SecKeyRef)generateRandomSymmetricKey {
    SecKeyRef cryptoKey = NULL;
    CFErrorRef error = NULL;

    // Create the dictionary of key parameters
    CFMutableDictionaryRef parameters = (__bridge CFMutableDictionaryRef)[NSMutableDictionary dictionaryWithObjectsAndKeys:kSecAttrKeyTypeAES, kSecAttrKeyType, (__bridge CFNumberRef)[NSNumber numberWithInt:256], kSecAttrKeySizeInBits, nil];

    // Generate a symmetric key based on the parameters
    cryptoKey = SecKeyGenerateSymmetric(parameters, &error);

    return cryptoKey;
}

- (CFDataRef)exportSymmetricKeyAsCFData:(SecKeyRef)cryptoKey {  
    // Create and populate the parameters object with a basic set of values
    SecItemImportExportKeyParameters params;

    params.version = SEC_KEY_IMPORT_EXPORT_PARAMS_VERSION;
    params.flags = 0;
    params.passphrase = NULL;
    params.alertTitle = NULL;
    params.alertPrompt = NULL;
    params.accessRef = NULL;
    // These two values are for import
    params.keyUsage = NULL;
    params.keyAttributes = NULL;

    // Create and populate the key usage array
    CFMutableArrayRef keyUsage = (__bridge CFMutableArrayRef)[NSMutableArray arrayWithObjects:kSecAttrCanEncrypt, kSecAttrCanDecrypt, nil];

    // Create and populate the key attributes array
    CFMutableArrayRef keyAttributes = (__bridge CFMutableArrayRef)[NSMutableArray array];

    // Set the keyUsage and keyAttributes in the params object
    params.keyUsage = keyUsage;
    params.keyAttributes = keyAttributes;

    // Set the external format and flag values appropriately
    SecExternalFormat externalFormat = kSecFormatUnknown; // Should result in the default appropriate external format for the given key.
    int flags = 0;

    // Export the CFData Key
    CFDataRef keyData = NULL;
    CFShow(cryptoKey);
    OSStatus oserr = SecItemExport(cryptoKey, externalFormat, flags, &params, &keyData);
    if (oserr) {
        fprintf(stderr, "SecItemExport failed (oserr= %d)\n", oserr);
        exit(-1);
    }

    NSLog(@"Exported Symmetric Key Data: %@", [(__bridge NSData *)keyData bytes]);
    return keyData;
}

但我最终在我的日志中得到的是：

SecItemExport 失败 (osrr= -25316)

“osrr= -25316”在 SecBase.h 中定义为：

errSecDataNotAvailable = -25316, /* 无法检索此项目的内容。*/

我最初认为该错误意味着 SecKeyRef 已提前发布或类似的东西，但正如您从日志中看到的那样，SecKey 报告自己很好。

关于我在这里遗漏或做错了什么的任何想法？谢谢！

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1 回答 1

4

在与 Apple 交谈后，事实证明这个问题是由“Extractable”属性设置为 NO 引起的，但无法使用SecKeyGenerateSymmetric()

已经提交了一个错误，但基本上在解决该错误之前，解决方案是使用 depreciated 方法SecKeyGenerate()。

而不是- (SecKeyRef)generateRandomSymmetricKey上面的方法使用这个：

- (SecKeyRef)generateRandomSymmetricKey {
    SecKeyRef symmetricKey;

    OSStatus oserr = SecKeyGenerate(NULL, CSSM_ALGID_AES, 256, 0, (CSSM_KEYUSE_DECRYPT | CSSM_KEYUSE_ENCRYPT), CSSM_KEYATTR_EXTRACTABLE, NULL, &symmetricKey);
    if (oserr) {
        NSLog(@"SecKeyGenerate failed: %@", (__bridge NSString *)SecCopyErrorMessageString(oserr, NULL));
        exit(-1);
    }

    return symmetricKey;
}

我希望这可以帮助别人。

于 2011-10-07T17:15:29.323 回答