仅使用ServiceName获取存储在Keychain中的用户名？或者:你应该在哪里存储用户名？

Question

所以OS X Keychain有三条信息:

• ServiceName(我的应用程序的名称)
• 用户名
• 密码

我显然总是知道ServiceName.有没有办法找到该ServiceName的任何已保存用户名？(一旦知道用户名,就很容易找到密码.)

我更喜欢使用一个漂亮的Cocoa包装器,如EMKeychain来做到这一点.但EMKeychain要求UserName获取任何钥匙串项目!

+ (EMGenericKeychainItem *)genericKeychainItemForService:(NSString *)serviceNameString withUsername:(NSString *)usernameString;

如果您需要用户名来查找凭据,您希望如何充分利用钥匙串中的保存凭据？将用户名保存在.plist文件中的最佳做法是什么？

Answer 1

SecKeychainFindGenericPassword只返回一个钥匙串项.要查找特定服务的所有通用密码,您需要在钥匙串上运行查询.根据您定位的OS X版本,有多种方法可以执行此操作.

如果您需要在10.5或更低版本上运行,则需要使用SecKeychainSearchCreateFromAttributes.这是一个相当可怕的API.下面是一个返回将用户名映射到密码的字典的方法的粗略剪辑.

- (NSDictionary *)genericPasswordsWithService:(NSString *)service {
    OSStatus status;

    // Construct a query.
    const char *utf8Service = [service UTF8String];
    SecKeychainAttribute attr = { .tag = kSecServiceItemAttr, 
                                  .length = strlen(utf8Service), 
                                  .data = (void *)utf8Service };
    SecKeychainAttribute attrList = { .count = 1, .attr = &attr };
    SecKeychainSearchRef *search = NULL;
    status = SecKeychainSearchCreateFromAttributes(NULL, kSecGenericPasswordItemClass, &attrList, &search);
    if (status) {
        report(status);
        return nil;
    }

    // Enumerate results.
    NSMutableDictionary *result = [NSMutableDictionary dictionary];
    while (1) {
        SecKeychainItemRef item = NULL;
        status = SecKeychainSearchCopyNext(search, &item);
        if (status)
            break;

        // Find 'account' attribute and password value.
        UInt32 tag = kSecAccountItemAttr;
        UInt32 format = CSSM_DB_ATTRIBUTE_FORMAT_STRING;
        SecKeychainAttributeInfo info = { .count = 1, .tag = &tag, .format = &format };
        SecKeychainAttributeList *attrList = NULL;
        UInt32 length = 0;
        void *data = NULL;
        status = SecKeychainItemCopyAttributesAndData(item, &info, NULL, &attrList, &length, &data);
        if (status) {
            CFRelease(item);
            continue;
        }

        NSAssert(attrList->count == 1 && attrList->attr[0].tag == kSecAccountItemAttr, @"SecKeychainItemCopyAttributesAndData is messing with us");
        NSString *account = [[[NSString alloc] initWithBytes:attrList->attr[0].data length:attrList->attr[0].length encoding:NSUTF8StringEncoding] autorelease];
        NSString *password = [[[NSString alloc] initWithBytes:data length:length encoding:NSUTF8StringEncoding] autorelease];
        [result setObject:password forKey:account];

        SecKeychainItemFreeAttributesAndData(attrList, data);
        CFRelease(item);
    }
    CFRelease(search);
    return result;
}

对于10.6及更高版本,您可以使用稍微不那么不方便的SecItemCopyMatchingAPI:

- (NSDictionary *)genericPasswordsWithService:(NSString *)service {
    NSDictionary *query = [NSDictionary dictionaryWithObjectsAndKeys:
                           kSecClassGenericPassword, kSecClass,
                           (id)kCFBooleanTrue, kSecReturnData,
                           (id)kCFBooleanTrue, kSecReturnAttributes,
                           kSecMatchLimitAll, kSecMatchLimit,
                           service, kSecAttrService,
                           nil];
    NSArray *itemDicts = nil;
    OSStatus status = SecItemCopyMatching((CFDictionaryRef)q, (CFTypeRef *)&itemDicts);
    if (status) {
        report(status);
        return nil;
    }
    NSMutableDictionary *result = [NSMutableDictionary dictionary];
    for (NSDictionary *itemDict in itemDicts) {
        NSData *data = [itemDict objectForKey:kSecValueData];
        NSString *password = [[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding] autorelease];
        NSString *account = [itemDict objectForKey:kSecAttrAccount];
        [result setObject:password forKey:account];
    }
    [itemDicts release];
    return result;
}

对于10.7或更高版本,您可以使用我精彩的LKKeychain框架(PLUG!).它不支持构建基于属性的查询,但您只需列出所有密码并过滤掉您不需要的密码.

- (NSDictionary *)genericPasswordsWithService:(NSString *)service {
    LKKCKeychain *keychain = [LKKCKeychain defaultKeychain];
    NSMutableDictionary *result = [NSMutableDictionary dictionary];
    for (LKKCGenericPassword *item in [keychain genericPasswords]) {
        if ([service isEqualToString:item.service]) {
            [result setObject:item.password forKey:item.account];
        }
    }
    return result;
}

(我没有尝试运行,甚至没有编译上面的任何代码示例;抱歉任何错别字.)

Answer 2

通用密码具有服务名称和用户名的唯一密钥。因此，要获取单个通用钥匙串条目，您需要提供两者。但是，您可以使用该函数迭代给定服务的所有通用钥匙串条目SecKeychainFindGenericPassword。

（免责声明：我对在 EMKeychain 中执行此操作一无所知。）