I have only seen the specification pattern used to retrieve data, but not to validate it. A colleague suggested I can use the specification pattern to “validate” an object so it does not become invalid when saving changes.
As an example, say we have a root Customer object that has a value for Address. We can track the changes to the object and create a specification that can be sent to the unit of work to make sure the address is valid (Has a physical address, city, and state) before changes are saved.
Any thoughts about this?
Following is a good read regarding differences between a specification and a validaton
http://lostechies.com/jimmybogard/2007/10/25/specifications-versus-validators/
Related
I need to store the values of devices' attributes with the right type in OrionCB's MongoDB.
As I was unable to perform that I dived into the code and found that IoTAgentUL (as well as IoTAgentJSON) uses OrionCB's API v1 instead of API v2.
As I can see API v1's updateContext sends data to MongoDB without it's type, so every measure is stored as text.
In the other hand I found that API v2's update entity send data to MongoDB with it's type. It produces that I can store attribute's values with it's type which benefits me when manipulating data (i.e. creating indexes, sorting, etc).
My question is if is there any workaround to solve this using the current implementations of IoT Agents.
The only workaround I can imagine is, once entities are automatically created by the IoT Agents, to update the type of such entities by your own. I mean, AFAIK, you can update both the value and the type of an entity.
In more details, I can think on a script that subscribes for all entities of certain type (those created by the agents). Then, when an entity is created this is notified to the script, which automatically updates the type of the entity's attributes.
Please observe you only need to modify the attribute's types once, just when the entities are created, not when an entity's attribute is updated; thus, something like an array or cache of already modified entities is needed in your script.
I am trying to work with a service that its creators describe as "restful"
To make a request to this service I have to post some Json e.g.
{
"#type" : "Something"
"$value" : 1
}
This is posted to a URL similar to this;
https://someSite.com/api/query/execute
No matter what the nature of the request, whether I am retrieving info, adding or updating it I must always use this URL (along with some header values to verify my credentials). The effects of posting to this service are determined by the JSON I send.
Depending on the nature of the call I will receive some JSON very similar to the sample above. This JSON never includes another URL (or part of one). It is always a "data object" i.e. a set of properties and their values. Sometimes I receive an empty response but know that the request has had an effect because I can view those effects through a website provided by the service provider
I have particular issues with ENUM values that I must send because I have no idea of the allowed values (they are always passed as strings)
No documentation has been provided for this service.
I am relatively new to RESTful services and JSON and would like to know whether this is truly a restful service, and if not why not?
Due to my lack of experience in this area I may have omitted some important information that would be required to properly answer this question. I will watch the comments closely and try to provide any additional clarification requested
know whether this is truly a restful service, and if not why not?
It isn't.
One of the main principles of REST is that "things" are identified by URLs. Having a single URL for all interaction with the API violates that principle.
For our last week in school (finals next week) our teacher decided to give us a crash course in Perl. We talked about all the differences we would encounter if we used Perl and then we started talking about "spoofing".
We were given an HTML example where a user could input their first and last names. Of course our example already had Mickey as the first name and Mouse as the last name.
<form action="action_page.php">
First name:<br>
<input type="text" value="Mickey">
<br>
Last name:<br>
<input type="text" name="lastname" value="Mouse">
<br><br>
<input type="submit" value="Submit">
</form>
At the end when you hit submit you were redirected to a new screen that said your first name is Mickey and your last name is Mouse.
Our teacher said "spoofing" is when you change the method = get in the URL so instead of having
firstname=Mickey&lastname=Mouse
you would enter something like
firstname=baseball&lastname=bat
That would instantly alter the intended command and you would end up getting first name as baseball and lastname as bat.
This all sounds pretty straight forward, until he said he wanted us to write a program to prevent spoofing without using a post method.
Instead when a user attempts to spoof the system we're supposed to print out some anti-spoofing comment.
Unfortunately, we never really talked about spoofing aside from the examples. I've attempted to Google spoofing to see some example code, or at least understand this concept, but I haven't had much luck, or I haven't looked in the right places.
So I thought I would ask here. Can someone who is decent at Perl direct me towards basic anti-spoofing programs and content, or at least explain and show how spoofing is supposed to work.
What you need to do is to authenticate the data in the query string, and validate it when you receive it. There is a standard tool(set) for this: a cryptographic Message Authentication Code (MAC).
Basically, a MAC is a function that takes in a message (any arbitrary string) and a secret key, and outputs a random-looking token that depends, in a complicated way, on both the message and the key. Importantly, it is effectively impossible to compute a valid MAC token for a modified message without knowing the key.
To validate a query string (or some other data) with a MAC, you'd basically follow these steps:
Encode the data into a "canonical" form as a string. For an HTTP URL, you could just use the query string (and/or the entire URL) as it is, although you may wish to normalize it e.g. by %-decoding any characters that don't have to be encoded, and normalizing the case of any %-encoded values (e.g. %3f → %3F).
Alternatively, you could decode the query string into, say, an associative array, and serialize this array in a format of your choice. This can make it easier to combine parameters from multiple sources (e.g. hidden form fields), to add extra data fields (see below) and to choose which fields you want to validate.
Optionally, combine the data with any additional information you wish to associate it with, such as a user ID and/or a timestamp. (You can either transmit the timestamp explicitly, or just round it down to, say, the last hour, and check both the current and the previous timestamp when validating it.) Changing any of these values will change the MAC output, thus preventing attackers from e.g. trying to submit one user's data under another user's account.
Store a secret key (preferably, a securely generated random value of, say, 128 bits) on the server. Obviously, this secret key must be stored so that users cannot access it (e.g. by guessing the path to the config file).
Feed the canonically encoded data and the secret key into the MAC algorithm. Take the result and (if your MAC library doesn't do this for you) encode it in some convenient matter (e.g. using the URL-safe Base64 variant).
Append the encoded MAC token as an extra parameter in the URL.
When you receive the data back, remove the MAC token, feed the rest of the data back into the MAC generation code as described above, and check that the resulting MAC matches the one you received.
MAC algorithms can be constructed from cryptographic hash functions like MD5 or SHA-1/2/3. In fact, a basic MAC can be obtained simply by concatenating the secret and the message, hashing them, and using the result as the token.
For some hash functions, like SHA-3, the simple MAC construction described above is actually believed to be secure; for older hash functions, which were not explicitly designed with this use in mind, however, it's safer to use the (slightly) more complicated HMAC construction, which hashes the input twice.
Alternatively, there are also MAC algorithms, such as CMAC, which are based on block ciphers (like AES) instead of hash functions. In some cases (e.g. on embedded platforms, where a fast hash function may not be available) these may be more efficient than HMAC; for a web application, however, the choice is essentially a matter of taste.
One difference between GET and POST is that the information for the former is passed in the URL itself. That means you can type what you like in the browser's address bar -- it doesn't have to have come from an HTML form. I think that's what is meant by spoofing here.
The most obvious protection is to calculate a CRC of all the protected fields -- in this case MickeyMouse -- and put that value in a hidden field of the HTML form sent out by the server. Then, when the request comes back, calculate the CRC of the same fields and check that it matches the value of the returned hidden field.
Of course that can be circumvented if the user works out how the protection functions and adds his own calculation of the CRC of his spoofed data as well. But this should be sufficient for a proof of concept.
If you want to detect if a user has changed a parameter in the querystring of a url after a form has performed a GET action, then generate a client side hash before the form is submitted. The hash would be based on the values of the form fields, and then compared to a recalculated hash based on the current parameter values on the response page. If the hashes don't match the querystring has been tampered with.
Here's a client side Crypto library to calculate the hashes https://code.google.com/p/crypto-js/
Note this is only for educational use, and wouldn't provide enough security in the real world, as a person could also discover the hashing key by inspecting the page source and use that to generate their own hashes.
A POST method wouldn't prevent spoofing anyway. POST and GET do almost exactly the same thing - they send plain text encoded variables to a web server.
They're insanely easy to "spoof" - the point isn't the spoofing, it's that you shouldn't trust "user input" like that, ever.
I would suggest in the case of the names, it doesn't matter. So what if I fudge your web page to "pretend" I am called "baseball bat" instead?
If it's important, like for example, ensuring I can only see my test results - then you need to handle the data processing server side. One method of doing this is via session tracking - so rather than including field in a web form, I instead use a "session token".
You would 'send' me a username and password - ideally using a hash to make it impossible to 'see' as you're sending it, or in your browser history. And then I would check it against my server, to check if that hash is 'valid' by performing the same operation on the server, and comparing the two.
So perlishly:
#!/usr/bin/perl
use strict;
use warnings;
use Digest::SHA qw ( sha1_base64 );
my ( $firstname, $lastname ) = qw ( Mickey Mouse );
my $timewindow = int ( time / 300 );
my $token = sha1_base64 ( $timewindow.$firstname.$lastname );
print $token;
This produces a token that doesn't last long - it changes every 5 minutes - but it's extremely difficult to tamper with.
The reason for including the time, is to avoid replay attacks, whereby if look in your browser history, I can find "your" token and reuse it. (That's probably the next question after the "spoofing" one though :))
If you sent the parameters with the token, bear in mind that it's actually quite easy for a malicious actor to perform the same calculation themselves, and send some completely faked credentials and tokens.
This is something of a simplistic example though - because really, faked parameters shouldn't matter, because you shouldn't trust them in the first place. If 'Mickey Mouse' is valid, and 'baseball bat' isn't, then your server should detect that when processing the form, and discard the latter, which makes the whole 'form spoofing' thing irrelevant.
The question is rather narrowly phrased, so this answer might not quite address what you're asking. But as a matter of policy, if you don't want your users to tamper with your data you should not give them custody of it. Why are you relying on the query string for the user name if the server already knows it? Rely on the client for authentication and for new information, and rely on your records for any information that should stay beyond the user's control.
POST requests can be crafted almost as easily as GET requests, and cryptographic protection, even when it is secure, is only useful to the extent that the client cannot access
the encrypted data; so why transmit it back and forth?
I'm attempting to move an existing (and working) client-side jQuery validation schema to JSONSchema to allow myself to validate arbitrary JSON on both the client and server.
My application is essentially a bunch of gigantic forms with lots of complex logic determining which questions should be asked based on the user's response to other questions. The forms each have over 200 fields.
Right now I'm only doing client-side validation and that works well about 99% of the time. Browser issues have cropped up on a few occasions, but nothing catastrophic. That being said, I want to do server-side validation (!).
After reading the JSONSchema draft and browsing around some of the v3 implementations, it seems like I might lose some of the more complex rules that my application has come to depend upon. I want to be sure that I'm not missing something before moving too far in any direction.
Some examples:
"If x == 10, then y is required, otherwise it's optional"
10 could be a literal value, an enum, etc., but I need to be able to reference another field in the same structure and guarantee it's value not only exists, but is equivalent to a specific type / value.
I think this is addressed in this thread on the JSONSchema list.
"If x = today's date, and y = tomorrow's date, then x > y"
This logic will be used to ensure that the "from" date comes before the "to" date.
From what I can see there's nothing like this and the only way I can see doing it is passing in a freshly eval-ed chunk of JSON as the schema.
The closest thing I've found to meet the above needs is CERNY.
If I'm barking up the wrong tree, please let me know. I'm also looked into running backbone.js on both the client and server.
tl;dr;
I want to maintain one set of validation rules for large and complex forms and apply these validation rules to arbitrary JSON documents on both the client and server side.
there is many tricks but not all of them are possible. For example
if x == 10 then y is required can be achieved with something like (draft 3):
"type":[
{"properties":{"x":{"enum":[10]}, "y":{"required":true}}},
{"properties":{"x":{"disallow":[{"enum":[10]}]}}}
]
Let's say, it's possible but very tricky… a schema is basically supposed to validate the structure, not it's content (even if there is few properties for this)
Another possible way I personally do like is to "extend" the current validation graph with an external url based schema. The idea is to send parameters of the current document on an url which one will return a relevant schema according to those parameters.
Example:
{
"extends":{"$ref":"http://checkCustomValidity/{x}/{y}/"};
}
Where at "runtime" the schema sent back could be a {"disallow":"any"} if not allowed or {} if ok
This is useful as the url can be both used for the client and server side (your client will not be completely standalone but in some cases, you just cannot)
A real life usage for this is in cases where it is obliged to use a remote service. For example if I do have to check if my nickname is already used on the server during the registration. I code a server side web service answering to the request path: http://www.server.com/isNicknameUsed/{nickname}
On a form of my web app, I've got a hidden field that I need to protect from tampering for security reasons. I'm trying to come up with a solution whereby I can detect if the value of the hidden field has been changed, and react appropriately (i.e. with a generic "Something went wrong, please try again" error message). The solution should be secure enough that brute force attacks are infeasible. I've got a basic solution that I think will work, but I'm not security expert and I may be totally missing something here.
My idea is to render two hidden inputs: one named "important_value", containing the value I need to protect, and one named "important_value_hash" containing the SHA hash of the important value concatenated with a constant long random string (i.e. the same string will be used every time). When the form is submitted, the server will re-compute the SHA hash, and compare against the submitted value of important_value_hash. If they are not the same, the important_value has been tampered with.
I could also concatenate additional values with the SHA's input string (maybe the user's IP address?), but I don't know if that really gains me anything.
Will this be secure? Anyone have any insight into how it might be broken, and what could/should be done to improve it?
Thanks!
It would be better to store the hash on the server-side. It is conceivable that the attacker can change the value and generate his/her own SHA-1 hash and add the random string (they can easily figure this out from accessing the page repeatedly). If the hash is on the server-side (maybe in some sort of cache), you can recalculate the hash and check it to make sure that the value wasn't tampered with in any way.
EDIT
I read the question wrong regarding the random string (constant salt). But I guess the original point still stands. The attacker can build up a list of hash values that correspond to the hidden value.
Digital Signature
Its probably overkill, but this sounds no different than when you digitally sign an outgoing email so the recipient can verify its origin and contents are authentic. The tamper-sensitive field's signature can be released into the wild with your tamper-sensitive field with little fear of undetectable tampering, as long as you protect the private key and verify the data and the signature with the public key on return.
This scheme even has the nifty property that you can limit "signing" to very protected set of servers/processes with access to the private key, but use a larger set of servers/processes provided with the public key to process form submissions.
If you have a really sensitive "do-not-tamper" field and can't maintain the hash signature of it on the server, then this is the method I would consider.
Although I suspect most are familiar with digital signing, here's some Wikipedia for any of the uninitiated:
Public Key Cryptography - Security
... Another type of application in
public-key cryptography is that of
digital signature schemes. Digital
signature schemes can be used for
sender authentication and
non-repudiation. In such a scheme a
user who wants to send a message
computes a digital signature of this
message and then sends this digital
signature together with the message to
the intended receiver. Digital
signature schemes have the property
that signatures can only be computed
with the knowledge of a private key.
To verify that a message has been
signed by a user and has not been
modified the receiver only needs to
know the corresponding public key. In
some cases (e.g. RSA) there exist
digital signature schemes with many
similarities to encryption schemes. In
other cases (e.g. DSA) the algorithm
does not resemble any encryption
scheme. ...
If you can't handle the session on the server, consider encrypting the data with your private key and generating an HMAC for it, send the results as the hidden field(s). You can then verify that what is returned matches what was sent because, since no-one else knows your private key, no-one else can generate the valid information. But it would be much better to handle the 'must not be changed' data on the server side.
You have to recognize that anyone sufficiently determined can send an HTTP request to you (your form) that contains the information they want, which may or may not bear any relation to what you last sent them.
If you can't/won't store the hash server side, you need to be able to re-generate it server-side in order to verify it.
For what it's worth, you should also salt your hashes. This might be what you meant when you said:
concatenated with a constant long
random string (i.e. the same string
will be used every time)
Know that if that value is not different per user/login/sesison, it's not actually a salt value.
As long as you guard the "constant long random string" with your life then your method is relatively strong.
To go further, you can generate one time / unique "constant long random string"'s.
What you are describing is similar to part of the implementation required for what are termed canaries and are used to mitigate Cross Site Request forgery attacks.
Generally speaking, a hidden input inside a HTML form contains an encrypted value that is posted back with a HTTP request. A browser cookie or a string held in session contains the same encrypted value such that when the hidden input value is decrypted and the cookie/session value is decrypted, the unencrypted values are compared to each other - if they are not identical, the HTTP request cannot be trusted.
The encrypted value might be an object containing properties. For example, in ASP.NET MVC, the canary implementation uses a class that contains properties for the authenticated username, a cryptographically pseudo random value generated using the RNGCryptoServiceProvider class, the DateTime (UTC format) at which the object was created and an optional salt string. The object is then encrypted using the AES Encryption algorithm with a 256 bit key and decrypted with the same key when the request comes in.