Don’t Disrespect the Web.Config – Encryption

As stated in an earlier post…

There are 3 things every public website should be doing with their web.config

1. Use web.config transforms to keep track of development versus production settings
2. Encrypt important configuration sections for security
3. ELMAH – Error Logging Modules and Handlers

In this post, we’ll discuss how to encrypt sensitive sections of the web.config so passwords and other information cannot be easily read by those who gain access to the file.

Why is it important?

Encrypting sensitive sections of the web.config is important because they are just that, sensitive. Think about your production web.config file. It may contain all sorts of data that you would not want to be accessible. There are often passwords for SQL database connections, passwords to an SMTP server, API Keys, or critical information for whatever system is being automated. In addition, web.config files are usually treated as just another source code file. There are probably many versions in your source control system right now. That means, any developer on the team, or more accurately anyone with access to the source code, can see what information is in the web.config file.

In many cases, storing passwords in a web.config is itself unnecessary and should be avoided. However, we know it is all too easy to fall into the trap of placing them in this flexible, convenient file. Therefore, at the very least, certain sections should be encrypted so they cannot be easily read or used for evil.

Encrypting ConnectionStrings

In our example, we will encrypt two typical configuration sections: ConnectionStrings and AppSettings on a Windows 7 development machine.

Follow the below steps:

1. Open a command prompt with elevated, Administrator, privileges:

2. At the command prompt, enter:

cd “C:\Windows\Microsoft.NET\Framework\v4.0.30319”

3. Now enter the following to encrypt the ConnectionStrings section:

aspnet_regiis.exe -pef “connectionStrings” “C:\WebApplication1\WebApplication1”

In this case, C:\WebApplication1\WebApplication1 is the directory where our web.config is located.

4. Enter the following to encrypt the AppSettings section:

aspnet_regiis.exe -pef “appSettings” “C:\WebApplication1\WebApplication1”

For reference on all the command-line options of aspnet_regiis.exe, refer to this MSDN page.

Decrypting ConnectionStrings

Of course, it is possible you might need to be able to read the original, unencrypted, data at a later time. To access that information is easy. Simply perform the previous steps but use the command-line option “-pdf” to decrypt the important sections.

Deployment

Deploying your web application with encrypted web.config sections is simple, but it may not be obvious. This StackOverflow answer explains the steps best. Generally, any server or development machine that uses the same encrypted web.config data must use the same RSA key pair, which can be exported using the aspnet_regiis tool.

Before and After

There you have it. You have successfully encrypted 2 sections of your web.config file. Take a look below to observe the before and after results:

Before

<connectionStrings>

<add name=“ApplicationServices“ connectionString=“data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|\aspnetdb.mdf;User Instance=true”
providerName=“System.Data.SqlClient“ />

</connectionStrings>

After

<connectionStrings configProtectionProvider=“RsaProtectedConfigurationProvider“>

<EncryptedData Type=“http://www.w3.org/2001/04/xmlenc#Element”
xmlns=“http://www.w3.org/2001/04/xmlenc#“>

<EncryptionMethod Algorithm=“http://www.w3.org/2001/04/xmlenc#tripledes-cbc“ />

<KeyInfo xmlns=“http://www.w3.org/2000/09/xmldsig#“>

<EncryptedKey xmlns=“http://www.w3.org/2001/04/xmlenc#“>

<EncryptionMethod Algorithm=“http://www.w3.org/2001/04/xmlenc#rsa-1_5“ />

<KeyInfo xmlns=“http://www.w3.org/2000/09/xmldsig#“>

<KeyName>Rsa Key</KeyName>

</KeyInfo>

<CipherData>

<CipherValue>fK275KFHx9RKip16DTpwxLi4AHpvCpat4S3edgsDwco9PgudsMKc1qAyh9qNt2y+90qV4QIzyZXm8j27UV5J+R5rNruMUOROLWzVt8qkRYRM3ADoiCi5BJh2SsjE0guGXFbufZDgRpPFV5bstgZSBPYNiYXQF/aOLyQjPCE8VDo=</CipherValue>

</CipherData>

</EncryptedKey>

</KeyInfo>

<CipherData>

<CipherValue>CSdausUH7yWcY8t1sPUqiCooYreEauzi4t33gVJuWYcfhspsguTchJjwthUTMLqnulYRmCu8ZnhrVBepQo7PHO/4k5mwo3s46TsgFddvvUlyY/EDQf047LG0pocBDxL3MgIGf3b+atoG29Jg0Wnhj+M6urYG55Ko4nGp36JILQptlEn+sqCl2sQ99izykXtRWP7kC4tldO+YvBuZ7x8fyGoANwSKQFo7cH+dbydvCkRvaFQsRATdsQKGmSrXwIlkoNvxFb1CBPx0qDenyCs+vO4QyF2CZ8QB+UIJzA8EL7W/FovH5zDczjXQWTsFSmsI+vSojl9G9jSVLJFbwOpQBLIKxfximl5r</CipherValue>

</CipherData>

</EncryptedData>

</connectionStrings>

In a future blog post, we will discuss the 3^rd party component ELMAH, which is vital to being notified when your users encounter exceptions in your web application.

Update 07/24/2012
It is possible to combine encryption with web.config transforms. I know this will work as I have done it before.

In my experience, I’ve done the following. I had to add an RSA section at the top of my web.config. For me, this went into my web.config.release as I did not encrypt my default/development web.config:

<configProtectedData defaultProvider=”MyRsaProtectedConfigurationProvider” xdt:Transform=”Insert”>
<providers>
<add name=”MyRsaProtectedConfigurationProvider”
type=”System.Configuration.RsaProtectedConfigurationProvider, System.Configuration, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL”
keyContainerName=”NetFrameworkConfigurationKey_viternuscom”
useMachineContainer=”true” />
</providers>
</configProtectedData>

Also, the web.config sections need to be replaced at the section level. You cannot replace the name or connection string attributes. So, you can use something like the below configuration to replace the whole connection strings section in each environment:

<connectionStrings configProtectionProvider=”MyRsaProtectedConfigurationProvider” xdt:Transform=”Replace”>
<EncryptedData Type=”http://www.w3.org/2001/04/xmlenc#Element&#8221;
xmlns=”http://www.w3.org/2001/04/xmlenc#”&gt;
<EncryptionMethod Algorithm=”http://www.w3.org/2001/04/xmlenc#tripledes-cbc&#8221; />
<KeyInfo xmlns=”http://www.w3.org/2000/09/xmldsig#”&gt;
<EncryptedKey xmlns=”http://www.w3.org/2001/04/xmlenc#”&gt;
<EncryptionMethod Algorithm=”http://www.w3.org/2001/04/xmlenc#rsa-1_5&#8243; />
<KeyInfo xmlns=”http://www.w3.org/2000/09/xmldsig#”&gt;
<KeyName>Rsa Key</KeyName>
</KeyInfo>
<CipherData>
<CipherValue>fV3NsFhZR/l0/5nvioFfjwjhhauNUTR96fQOK3QeRTW05ERDAQrFGj9MBt5Jh7Ca4rIS2JZfOfNTjTxWiEp/tjk+9LXVyPKrJYMiNlYiUmZGfV/amPsLPmRm2pOEyKwJhJLN6NyZdht/xGrf1ClDKO6CG1ViA5pK5R8Db8X9ul4=</CipherValue>
</CipherData>
</EncryptedKey>
</KeyInfo>
<CipherData>        <CipherValue>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</CipherValue>
</CipherData>
</EncryptedData>
</connectionStrings>

I hope this helps.