Author: Gaurab

Unable to resolve a reference to Microsoft.CSharp assembly in a .Net project.

In one of my projects I saw that the Microsoft.Csharp reference is not found.

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It was strange because for other projects the reference is resolved fine.

Resolution: Somehow my current project framework got pushed to v3.5.

I changed it to v4.0 and that fixed the issue.

It is important that you save the changes before the project framework is changed because the project will re load and you may lose any unsaved work.

HTTP 500 Internal Server Error – While deploying a website created in ASP.Net and .Net framework 4.0 in IIS 7.5.

 

I created a website in ASP.Net and published it to a location in the hard drive within the default projects folder of VS2010 (C:\Users\\Documents\Visual Studio 2010\Projects\\PrecompiledWeb).

This was a simple website project, nothing fancy, that looked like this:

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I created an Application in IIS 7.5 under local host (Root -> Sites -> Default Website) and provided the physical path of the website to the location of my precompiled bit. By default the AppPool used is the DefaultAppPool that by default runs on the AppPoolIdentity. But when I try to access the site I got the following:

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For me this error kept cropping up and the reason was that the account on which the app pool was running did not have access to the physical location of the website files. You can check the account by going to Application pool node -> Select the app pool -> click Advanced settings on the left menu and scroll down. Ensure that you provide read access to the physical location. Once you do the error goes away.

Entity Framework 4.0 – 2

Error 3 Error 5: The ‘Namespace’ attribute is invalid – The value ‘‘ is invalid according to its data type ‘http://schemas.microsoft.com/ado/2008/09/edm:TNamespaceName’ – The Pattern constraint failed.

This error may come up when you try to add a new blank “Ado.Net Entity Data Model” to your project and name the EDM with a character line _(underscore),-(hyphen), etc. in the name. I got this for this two values and there must be more.

The way to solve this error is to name the EDM without any special character in it.

This is for the records J

ADO.Net Entity Framework 4.0 – 1

Entity Framework 4.0: Pluralize or singularize generated object names

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One of the main additions to the Entity Framework 4.0 is the checkbox shown in the screenshot below:

Pluralize or singularize generated object names

In the previous versions of Entity Framework, by default the Entity Set Name and Entity Name were same, shown the screen shot below:

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This caused a lot of confusion for the developers when they started coding against the model.

In Entity Framework 4.0 a new feature has been introduced via the check box mentioned above. This check box is selected by default and provides, amongst others, for the pluralization or singularization of the Entity name. This checkbox practically follows the rule wherein it marked all Entity Types as singular and the Entity Set name as plural. Below is an example wherein this checkbox has been used to pluralize the Entity Set Name. You can uncheck the control to get back to the older – both name same format.

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Short Notes on Public Key Infrastructure–Part 1

The focal point of a PKI setup is the Certificate Authority, CA. The CA works as the Management hub for the digital certificates.

Considering that load on the CAs, some setup use an additional server called the Registration Authority (RA). The RA takes off some of the load from the CA by handling the verification of the data submitted to CA before the issue of the digital certificates. The RA acts as an interface between the user and the CA. The RA is generally found in the hierarchical model where the work load of the CA may need to be offloaded.

One of the main requirements of PKI is to be able to store public keys and certificates at a location that can be accessed by public. The public and the private key is created at the same time using the same predefined algorithm.

A digital certificate is a collection of predefined information related to the a component of the PKI setup, called the Public Key. The digital certificates use the X.509 standards. The X.509 standards allows the association between the users Distinguished name and the public key. The Distinguished Name is provided by the Naming authority and is used as a unique number while creating the certificate. A X.509 certificate generally contains the following:

  1. Serial Number:
  2. Subject: Name of the organization or the person identified.
  3. Signature Algorithm
  4. Issuer:
  5. Valid From:
  6. Valid To:
  7. Public Key
  8. Thumbprint Algorithm
  9. Thumbprint

Certificate Policy is the set if rules that indicate how exactly the certificate may be used. The CP is a plain text document that is assigned a unique object id so that anyone can reference it. A certificate can be used under multiple policies. For example, a digital certificate can be sued for:

  1. Access control
  2. Setting up of trusted connection
  3. System sign on
  4. Digitally sign documents.

Certificate Practice Statements explain how to implement the Certificate Policy. It describes how the CA plans to manage the certs it issues. All CAs should have CPS.

Digital certificates are revoked when the information they contain are no longer valid or trusted. The most common reason for the revocation of the digital certificates is the compromise of the private key. Note that certificate Revocation is different from Certificate expiration. A certificate can be revoked by the CA by confirming with the certificate owner or the PKI administrator.

Certificate Revocation List: X.509 standards require that a CRL gets published. CRLs contain the revocation status of =certificates that the CA manage. CRLs can be:

  1. Simple CRL
  2. Delta CRL

OCSP- Online Certificate Status Protocol: Returns the following details about a certificate queried:

  1. The cert status (good/revoked/unknown)
  2. The last update on the cert status
  3. The next time the status will be updated.
  4. The time when the response is sent.

….

Web Application Threat Modeling – Its Hot and Buzzing!!

Recently I flunked an interview wherein the interviewer was asking lots of questions around threat models. While I will not be putting any of those questions here, I did do my “after the horse bolted” type of post mortem and have come up with a list of questions that anyone who works with design of web application should be aware of.

First the obvious one Smile What is Threat Modeling?

Well It’s a hot buzzword these days in the world of Information technology security. Threat modeling is a structured approach to analyze your web application design and identify threats against your system. Hmnn of…you said THREAT? Threat model is very useful in identifying security issues related to design early in the application development lifecycle and thus makes mitigating those issues less costly as compared to identifying in the, say Verification phase.

So what is a Threat? Threat is a possible harm that can be caused to an Asset (anything of importance that needs protection; from a web application perspective it may be user passwords, keys, financial information, etc.)

Where and when do you start Threat Modeling? A good point to start threat modeling is just after you are done with the functional and technical design document of your application. Having said that it is never to late for you to start, if not in the current release, this may help in the next.

What are the general steps involved in Threat Modeling?

The threat modeling process should ideally start with a brain storming session to answer the following questions (by not means an exhaustive list..so think think think):

  1. What is asset to the system?
  2. Who are the end users?
  3. Where will you deploy the application? Is this an intranet application or will be accessible over internet?
  4. What would attract a malicious user to your system?
  5. What security mechanisms do you have in place?
  6. How many point of failures does this application have? One??? Run back to the drawing board…

While doing the threat model of an application (or anything) think like an attacker who is trying to sabotage your app. Find ways on subverting your system’s weaknesses. This will help you create an Attack Tree (a What??????)

Once you have identified the threats, what’s next? Remember risk can never be erased fully, you can only Transfer/Accept/Ignore the risk. And that’s exactly what you do once you have identified the threats. A good threat model will have ALL the identified threats reviewed and updated as Ignore/Accept/Transfer.

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Authentication and authentication protocols

Authentication is the one of the fundamental requirements for ensuring security of important assets. Authentication is the process of validating the identity of an object trying to access an asset. Authentication can be done based on the implementation of one or more the following:

  1. Authentication by what you know.
  2. Authentication by what you have.
  3. Authentication by what you are.

When attempting to authenticate a user/application several industry standard types of authentication may be used depending on various conditions that exists on a subjective basis.

Various types of authentication protocols that is supported by Microsoft Windows Server 2003 family includes:

  1. Kerberos v5 authentication.
  2. SSL/TLS authentication.
  3. NTLM authentication.
  4. Digest authentication.
  5. Passport authentication.

Kerberos v5 authentication protocols: This protocol is either used with password or a smart card for interactive logon. It is also the default method for network authentication of services. The process works like this:

  1. The user on a client system using a password or a smart card authenticates to the KDC.
  2. The KDC issues a TGT to the client. The client system uses the TGT to access the Ticket Granting Service (TGS) which is the part of the Kerberos V5 authentication mechanism on the domain controller.
  3. The TGS issues a service ticket to the client.
  4. The client supplies the required network service with the service ticket. The service ticket provides both the user identity to the service and also the service identity to the user.

So the Kerberos v5 authentication protocol has the following main parts:

  1. Key Distribution Center (KDC)
  2. Ticket Granting Ticket (TGT)
  3. Ticket Granting Service (TGS)

The Kerberos v5 services are installed on each domain controller and a Kerberos client is installed on each workstation and server.

Each domain controller acts as a KDC. The client service uses the DNS to look up for the nearest nearest domain controller and in turn the nearest KDC.

Beginning Windows Server 2003, Kerberos is implemented as a SSP (Security Service Provider) that can be accessed using the SSPI (Security Support Provider Interface)

SSL/TLS authentication Protocols: TLS/SSL authenticates and secures data transfer by using certificate based authentication and symmetric encryption keys. Windows Server 2003 onwards, SSL/TLS protocols are implemented as a Security Service Providers (SSP) using dynamic link libraries that are called SChalnnels that is supplied with the OS implementation. Which one gets used is decided based on the capability of the computer on the other side of the connection. The default SSPs for Windows Server 2003 include the following: Kerberos, Digest, NTLM, SChannel and Negotiate authentication protocols as DLLs in the SSPI.

SChannel SSP is used to access web enabled services such as emails and personal information served over the internet on web pages. The SChannel SSP uses the public key encryption to authenticate parties. It included four authentication protocols that it supports:

  1. TLS v1.0
  2. SSL v3.0
  3. SSL v2.0
  4. Also supports PCT (Private Communications Transport) for backward compatibility.

Schannel then selects the most preferred authentication protocol that both parties can support.

TLS/SSL Architecture: TLS/SSL protocols are layered between the Application layer and the TCP/IP layer, where it can secure and send the application data to the transport layer for farther transport. Just because TLS/SSL works between the application layer and the transport layer it can support multiple application layer protocols.

TLS/SSL assumes that TCP/IP is in use. The main advantage of using TLS/SSL is that it provide the following:

  1. Message Integrity
  2. Message confidentiality
  3. Message authentication

The step by step of how SSL/TLS works:

  1. Client tries to connect to a SSL/TLS enabled service on port 443. The browser will send out the information that will include its supported methods of encrypting data. This includes an encryption type, some random data that encryption program on both side can use in the scrambling routine, and other ssl related data.
  2. Server responds by sending its own random data to be used for the encryption as well as other ssl information that will include its SSL certificate with the public key that the browser will use in the subsequent steps.
  3. The client browser checks the information it has received and compares it to the domain it to the domain it was trying to connect securely with.If the secure certificate information on the web site doesn’t match the domain name the browser will notify the customer that there is a problem. The certificate expiration date and valid certificate authority are also checked at this point.
  4. After validating the server certificate, the browser uses a random data that it encrypts using the agreed upon encryption method. For encryption it uses the public key sent by the server and send this encrypted secret to the server.
  5. With the string that the server received from the browser, both the browser and the web server create a new string and use it to create session keys that their encryption programs use for the rest of the session to scramble and descramble (or encrypt/decrypt) all transmissions for the rest of the session. With the Master Secret key in place, both sides are also able to verify that the data didn’t change in route.

NTLM Authentication: NTLM is the abbreviation for Windows NT LAN Manager This is a Windows network authentication protocol that uses challenge/response system to allow a client to prove its identity without sending the password over the network.  NTLM is the authentication protocol for computers that are not participating in a domain, such as stand-alone servers and workgroups. NTLM is a challenge-response authentication protocol which uses three messages to authenticate a client in a connection oriented environment (connectionless is similar), and a fourth additional message if integrity is desired.

Kerberos has mostly replaced NTLM in domain controller environment within AD implementation, but NTLM still find wide spread usage in environments where the domain controller is unavailable or reachable.

Reference: http://technet.microsoft.com 

 

Information Security: Phishing and Microsoft Phishing filters

Phishing is one of the fastest growing threats of identity theft and abuse on the internet. It is so prevalent that almost any site of importance will have a warning mentioned somewhere to be careful about phishing attacks.

The very basis of Phishing attacks are phony websites that will give a perfect actual site like feeling to the user. This way the attackers manage to fool the user and get the important personal and financial information ranging from SSNs to credit card details.

Often phishing requests are sent over innocent looking emails that reflect the actual emails sent out by the legitimate organizations, requesting users for information. A not so tech savvy user may not be careful enough and hence loss of important information happens.

To fight against phishing scams, Microsoft has taken a number of steps that include:

1. Including SenderID to all of its email  email products and services

2. The Phishing filter (SmartScreen filter)

Per MSDN:

The Sender ID Framework is an e-mail authentication technology protocol that helps address the problem of spoofing and phishing by verifying the domain name from which e-mail messages are sent. Sender ID validates the origin of e-mail messages by verifying the IP address of the sender against the alleged owner of the sending domain.

The SmartScreen filter is a feature of Windows Internet Explorer 8. It is designed to help protect the user from fraudulent websites trying to steal personal information. SmartScreen filter also helps protect from installing malicious software or malware.

SmartScreen filter helps to protect you in three key ways:

  • It operates in the background as you browse the web, analyzing webpages and determining if they have any characteristics that might be suspicious. If it finds suspicious webpages, SmartScreen filter will display the “Are you trying to visit this website?” fly-out, giving you an opportunity to provide feedback and advising you to proceed with caution.
  • SmartScreen filter checks the sites you visit against an up-to-the-hour, dynamic list of reported phishing sites and malicious software sites. If it finds a match, SmartScreen filter will show you a red warning notifying you that the site has been blocked for your safety.
  • SmartScreen filter also checks files downloaded from the web against the same dynamic list of reported malicious software sites. If it finds a match, SmartScreen filter will show a red warning notifying you that the download has been blocked for your safety.

Application Security: Internet Explorer and Cross Site Scripting

Cross site scripting (aka XSS) is one of the most prevalent web application security issue. In OWASP top 10 for 2010, cross site featured prominently in number 2.

Considering the damage that a successful cross site scripting attack is capable of doing, almost all the successful commercial browsers have tried to provide security features that makes it difficult to execute a successful cross site scripting attack. One of the main ways this attack is carried out is by exploiting the browser’s capability for executing scripts.

Starting Internet Explorer 6 SP1, a new attribute is introduced to the cookies to counter the menace of XSS.

This attribute makes the cookie inaccessible to the scripts, thus stopping malicious script code from executing. The cookies with this attribute set are called HTTP only cookie.

A cookie is set on the client with an HTTP response header.

Set-Cookie: =[; =]
[; expires=][; domain=]
[; path=][; secure][; HttpOnly]

The HttpOnly attribute is not case sensitive and it is important to be noted that this feature must be used in coordination with other XSS mitigation to effectively counter XSS, like:

1. Proper input validation.

2. Adequate output encoding whenever any possible user controlled values are rendered back to the browser.