I have a restful service for the documents, where the documents are stored in mongodb, the restful api for the document is /document/:id, initially the :id in the api is using the mongodb 's object id, but I wonder deos this approach reveal the database id, and expose the potential threat, should I want to replace it with a pseudonymity id.
if it is needed to replace it the pseudonymity id, I wonder if there is a algorithmic methods for me to transform the object id and pseudonymity id back and forth without much computation
First, there is no "database id" contained in the ObjectID.
I'm assuming your concern comes from the fact that the spec lists a 3 byte machine identifier as part of the ObjectID. A couple of things to note on that:
Most of the time, the ObjectID is actually generated on the client side, not the server (though it can be). Hence this is usually the machine identifier for the application server, not your database
The 3 byte Machine ID is the first three bytes of the (md5) hash of the machine host name, or of the mac/network address, or the virtual machine id (depending on the particular implementation), so it can't be reversed back into anything particularly meaningful
With the above in mind, you can see that worrying about exposing information is not really a concern.
However, with even a small sample, it is relatively easy to guess valid ObjectIDs, so if you want to avoid that type of traffic hitting your application, then you may want to use something else (a hash of the ObjectID might be a good idea for example), but that will be dependent on your requirements.
Related
The normal MO for creating items in a database is to let the database control the generation of the primary key (id). That's usually true whether you're using auto-incremented integer ids or UUIDs.
I'm building a clientside app (Angular but the tech is irrelevant) that I want to be able to build offline behaviour into. In order to allow allow offline object creation (and association) I need the the client appplication to generate primary keys for new objects. This is both to allow for associations with other objects created offline and also to allow for indempotence (making sure I don't accidentally save the same object to the server twice due to a network issue).
The challenge though is what happens when that object gets sent to the server. Do you use a temporary clientside ID which you then replace with the ID that the server subsequently generates or you use some sort of ID translation layer between the client and the server - this is what Trello did when building their offline functionality.
However, it occurred to me that there may be a third way. I'm using UUIDs for all tables on the back end. And so this made me realise that I could in theory insert a UUID into the back end that was generated on the front end. The whole point of UUIDs is that they're universally unique so the front end doesn't need to know the server state to generate one. In the unlikely event that they do collide then the uniqueness criteria on the server would prevent a duplicate.
Is this a legitimate approach? The risk seems to be 1. Collisions and 2. any form of security that I haven't anticipated. Collisons seem to be taken care of by the way that UUIDs are generated but I can't tell if there are risks in allowing a client to choose the ID of an inserted object.
However, it occurred to me that there may be a third way. I'm using UUIDs for all tables on the back end. And so this made me realise that I could in theory insert a UUID into the back end that was generated on the front end. The whole point of UUIDs is that they're universally unique so the front end doesn't need to know the server state to generate one. In the unlikely event that they do collide then the uniqueness criteria on the server would prevent a duplicate.
Yes, this is fine. Postgres even has a UUID type.
Set the default ID to be a server-generated UUID if the client does not send one.
Collisions.
UUIDs are designed to not collide.
Any form of security that I haven't anticipated.
Avoid UUIDv1 because...
This involves the MAC address of the computer and a time stamp. Note that UUIDs of this kind reveal the identity of the computer that created the identifier and the time at which it did so, which might make it unsuitable for certain security-sensitive applications.
You can instead use uuid_generate_v1mc which obscures the MAC address.
Avoid UUIDv3 because it uses MD5. Use UUIDv5 instead.
UUIDv4 is simplest, it's a 122 bit random number, and built into Postgres (the others are in the commonly available uuid-osp extension). However, it depends on the strength of the random number generator of each client. But even a bad UUIDv4 generator is better than incrementing an integer.
Let's say we have two models like this:
User:
_ _id
- name
- email
Company:
- _id
_ name
_ slug
Now let's say I need to connect a user to the company. A user can have one company assigned. To do this, I can add a new field called companyID in the user model. But I'm not sending the _id field to the front end. All the requests that come to the API will have the slug only. There are two ways I can do this:
1) Add slug to relate the company: If I do this, I can take the slug sent from a request and directly query for the company.
2) Add the _id of the company: If I do this, I need to first use the slug to query for the company and then use the _id returned to query for the required data.
May I please know which way is the best? Is there any extra benefit when using the _id of a record for the relationship?
Agree with the 2nd approach. There are several issues to consider when deciding on which field to use as a join key (this is true of all DBs, not just Mongo):
The field must be unique. I'm not sure exactly what the 'slug' field in your schema represents, but if there is any chance this could be duplicated, then don't use it.
The field must not change. Strictly speaking, you can change a key field but the only way to safely do so is to simultaneously change it in all the child tables atomically. This is a difficult thing to do reliably because a) you have to know which tables are using the field (maybe some other developer added another table that you're not aware of) b) If you do it one at a time, you'll introduce race conditions c) If any of the updates fail, you'll have inconsistent data and corrupted parent-child links. Some SQL DBs have a cascading-update feature to solve this problem, but Mongo does not. It's a hard enough problem that you really, really don't want to change a key field if you don't have to.
The field must be indexed. Strictly speaking this isn't true, but if you're going to join on it, then you will be running a lot of queries on it, so you'll need to index it.
For these reasons, it's almost always recommended to use a key field that serves solely as a key field, with no actual information stored in it. Plenty of people have been burned using things like Social Security Numbers, drivers licenses, etc. as key fields, either because there can be duplicates (e.g. SSNs can be duplicated if people are using fake numbers, or if they don't have one), or the numbers can change (e.g. drivers licenses).
Plus, by doing so, you can format the key field to optimize for speed of unique generation and indexing. For example, if you use SSNs, you need to check the SSN against the rest of the DB to ensure it's unique. That takes time if you have millions of records. Similarly for slugs, which are text fields that need to be hashed and checked against an index. OTOH, mongoDB essentially uses UUIDs as keys, which means it doesn't have to check for uniqueness (the algorithm guarantees a high statistical likelihood of uniqueness).
The bottomline is that there are very good reasons not to use a "real" field as your key if you can help it. Fortunately for you, mongoDB already gives you a great key field which satisfies all the above criteria, the _id field. Therefore, you should use it. Even if slug is not a "real" field and you generate it the exact same way as an _id field, why bother? Why does a record have to have 2 unique identifiers?
The second issue in your situation is that you don't expose the company's _id field to the user. Intuitively, it seems like that should be a valuable piece of information that shouldn't be given out willy-nilly. But the truth is, it has no informational value by itself, because, as stated above, a key should have no actual information. The place to implement security is in the query, ensuring that the user doing the query has permission to access the record / specific fields that she's asking for. Hiding the key is a classic security-by-obscurity that doesn't actually improve security.
The only time to hide your primary key is if you're using a poorly thought-out key that does contain useful information. For example, an invoice Id that increments by 1 for each invoice can be used by someone to figure out how many orders you get in a day. Auto-increment Ids can also be easily guessed (if my invoice is #5, can I snoop on invoice #6?). Fortunately, Mongo uses UUIDs so there's really no information leaking out (except maybe for timing attacks on its cryptographic algorithm? And if you're worried about that, you need far more in-depth security considerations than this post :-).
Look at it another way: if a slug reliably points to a specific company and user, then how is it more secure than just using the _id?
That said, there are some instances where exposing a secondary key (like slugs) is helpful, none of which have to do with security. For example, if in the future you need to migrate DB platforms and need to re-generate keys because the new platform can't use your old ones; or if users will be manually typing in identifiers, then it's helpful to give them something easier to remember like slugs. But even in those situations, you can use the slug as a handy identifier for users to use, but in your DB, you should still use the company ID to do the actual join (like in your option #2). Check out this discussion about the pros/cons of exposing _ids to users:
https://softwareengineering.stackexchange.com/questions/218306/why-not-expose-a-primary-key
So my recommendation would be to go ahead and give the user the company Id (along with the slug if you want a human-readable format e.g. for URLs, although mongo _ids can be used in a URL). They can send it back to you to get the user, and you can (after appropriate permission checks) do the join and send back the user data. If you don't want to expose the company Id, then I'd recommend your option #2, which is essentially the same thing except you're adding an additional query to first get the company Id. IMHO, that's a waste of cycles for no real improvement in security, but if there are other considerations, then it's still acceptable. And both of those options are better than using the slug as a primary key.
Second way of approach is the best,That is Add the _id of the company.
Using _id is the best way of practise to query any kind of information,even complex queries can be solved using _id as it is a unique ObjectId created by Mongodb. Population is the process of automatically replacing the specified paths in the document with document(s) from other collection(s). We may populate a single document, multiple documents, plain object, multiple plain objects, or all objects returned from a query.
Hello Internet Denizens,
I was reading through a nice database design article and the final determination on how to properly generate DB primary keys was ...
So, in reality, the right solution is probably: use UUIDs for keys,
and don’t ever expose them. The external/internal thing is probably
best left to things like friendly-url treatments, and then (as Medium
does) with a hashed value tacked on the end.
That is, use UUIDs for internal purposes like db joins, but use a friendly-url for external purposes (like a REST API).
My question is ... how do you make uniquely identifiable (and friendly) keys for external purposes?
I've used several APIs: Stripe, QuickBooks, Amazon, etc. and it seems like they use straight up sequential IDs for things like customers, report IDs, etc for retrieving information. It makes me wonder if exposing UUIDs as a security risk is a little overblown b/c in theory you should be able to append a where clause to your queries.
SELECT * FROM products where UUID = <supplied uuid> AND owner/role/group/etc = <logged in user>
The follow-up question is: If you expose a primary key, how do people efficiently restrict access to that resource in a database environment? Assign an owner to a db row?
Interested in the design responses.
Potential Relevant Posts for Further Reading:
Should I use UUIDs for resources in my public API?
It is not a good idea to expose your internal ids to the outside. You should either encode them (with some algorithm) or have a look up table.
Also, do not append parameters provided by user (or URL) to your SQL query (UUIDS or not), this is prone to SQL injection. Use parameterized SQL queries for that.
Say I have a Products array in my Mongodb. I'd like users to be able to see each product on their own page: http://www.mysite.com/product/12345/Widget-Wodget. Since each Product doesn't have an incremental integer ID (12345) but instead it has a BSON ID (5063a36bdeb13f7505000630), I'd need to either add the integer ID or use the BSON ID.
Since BSON ID's include the PID:
4-byte timestamp,
3-byte machine identifier,
2-byte process id,
3-byte counter.
Am I exposing secure information to the outside world if I use the BSON ID in my url?
I can't think of any use to gain privileges on your machines, however using ObjectIds everywhere discloses a lot of information nonetheless.
By crawling your website, one could:
find about some hidden objects: for instance, if the counter part goes from 0x....b1 to 0x....b9 between times t1 and t2, one can guess ObjectIds within these invervals. However, guessing ids is most likely useless if you enforce access permissions
know the signup date of each user (not very sensitive info but better than nothing)
deduce actual (as opposed to publicly available) business hours from the timestamps of objects created by the staff
deduce in which timezones your audience lives from the timestamps of user-generated objects: if your website is one which people use mostly at lunchtime, then one could measure peaks of ObjectIds and deduce that a peak at 8 PM UTC means the audience was on the US West coast
and more generally, by crawling most of your website, one can build a timeline of the success of your service, having for any given time knowledge of: your user count, levels of user engagement, how many servers you've got, how often your servers are restarted. PID changes occurring on weekends are more likely crashes, whereas those on business days are more likely crashes + software revisions
and probably find other info specific to your business processes and domain
To be fair, even with random ids one can infer a lot. The main issue is that you need to prevent anyone from scraping a statistically significant part of your site. But if someone is determined, they'll succeed eventually, which is why providing them with all of this extra, timestamped info seems wrong.
Sharing the information in the ObjectID will not compromise your security. Someone could infer minor details such as when the ObjectID was created (timestamp), but none of the ObjectID components should be tied to authentication or authorization.
If you are building an e-commerce site, SEO is typically a strong consideration for public URLs. In this case you normally want to use a friendlier URL with shorter and more semantic path components than an ObjectID.
Note that you do not have to use the default ObjectID for your _id field .. so could always generate something more relevant for your application. The default ObjectID does provide a reasonable guarantee of uniqueness, so if you implement your own _id allocation you will have to take this into consideration.
See also:
Create an Auto-Incrementing Sequence Field
As #Stennie said, not really.
Let's start with the pid, most hackers wouldn't bother looking for a pid, on say Linux, instead they would just do:
ps aux | grep mongod
or something similar. Of course this requires the hacker to have actually hacked your server, I know of no public hack available based on the pid alone. Considering the pid will change when you restart the machine or mongod, this information is utterly useless to anyone trying to spy.
The machine id is another bit of data that is quite useless publicly and, to be honest, they would get a better understanding of your network using ping or digg than they would through the machine id alone.
So to answer the question: No, there is no real security threat and the information you are displaying is of no use to anyone except MongoDB really.
I also agree with #Stennie on using SEO friendly URLs, an example which I commonly use for e-commerce is /product/product_title_ with a smaller random id (maybe base 64 encode the _id) or a auto incrementing id with .html on the end.
document/show?id=4cf8ce8a8aad6957ff00005b
Generally I think you should be cautious to expose internals (such as DB ids) to the client. The URL can easily be manipulated and the user has possibly access to objects you don't want him to have.
For MongoDB in special, the object ID might even reveal some additional internals (see here), i.e. they aren't completely random. That might be an issue too.
Besides that, I think there's no reason not to use the id.
I generally agree with #MartinStettner's reply. I wanted to add a few points, mostly elaborating what he said. Yes, a small amount of information is decodeable from the ObjectId. This is trivially accessible if someone recognizes this as a MongoDB ObjectID. The two downsides are:
It might allow someone to guess a different valid ObjectId, and request that object.
It might reveal info about the record (such as its creation date) or the server that you didn't want someone to have.
The "right" fix for the first item is to implement some sort of real access control: 1) a user has to login with a username and password, 2) the object is associated with that username, 3) the app only serves objects to a user that are associated with that username.
MongoDB doesn't do that itself; you'll have to rely on other means. Perhaps your web-app framework, and/or some ad-hoc access control list (which itself could be in MongoDB).
But here is a "quick fix" that mostly solves both problems: create some other "id" for the record, based on a large, high-quality random number.
How large does "large" need to be? A 128-bit random number has 3.4 * 10^38 possible values. So if you have 10,000,000 objects in your database, someone guessing a valid value is a vanishingly small probability: 1 in 3.4 * 10^31. Not good enough? Use a 256-bit random number... or higher!
How to represent this number in the document? You could use a string (encoding the number as hex or base64), or MongoDB's binary type. (Consult your driver's API docs to figure out how to created a binary object as part of a document.)
While you could add a new field to your document to hold this, then you'd probably also want an index. So the document size is bigger, and you spend more memory on that index. Here's what you might not have though of: simply USE that "truly random id" as your documents "_id" field. Thus the per-document size is only a little higher, and you use the index that you [probably] had there anyways.
I can set both the 128 character session string and other collection document object ids as cookies and when user visits do a asynchronous fetch where I fetch the session, user and account all at once. Instead of fetching the session first and then after fetching user, account. If the session document is valid ill share the user and account documents.
If I do this I'll have to make every single request for a user and account document require the session 128 character session cookie to be fetched too thus making exposing the user and account object id safer. It means if anyone is guessing a user ID or account ID, they also have to guess the 128 string to get any answers from the system.
Another security measure you could do is wrap the id is some salt which you only know the positioning such as
XXX4cf8ce8XXXXa8aad6957fXXXXXXXf00005bXXXX
Now you know exactly how to slice that up to get the ID.