One of the best practices suggested while working with ASP.NET application is keeping values you want to make plug and play (changing them without changing the implementation) in web.config file. These configurable values can be anything ranging from some string constants to connection strings. Almost all the developers(at least those I know) follow this suggestion religiously. We keep these values in a readable format in web.config. Sometimes these values can have sensitive information like if we are storing connection string to our production database and if SQL server credentials are used to login to database server, then connection string will have username and password for the production database. Keeping credentials for database server unguarded can be a huge risk. Though IIS does a good job by blocking access to any resource with .config extension by default. But certainly there are many ways (leaving FTP open :)) by which someone with not so good intensions gets access to this config file containing credentials to database server. So, if one has this kind of sensitive data in config file then that data should be stored in encrypted way to mitigate risk of credentials falling under wrong hands.
This topic popped up while having a discussion with a colleague. He mentioned that .NET has some way of encrypting the values in config files. Which prompted me to search about this feature and Yes, .NET provides a very simple but effective way to encrypt values in config files. As you might already know, configuration settings in .NET work in provider model i.e. these settings can be replaced with another values without impacting the implementation.
.NET framework provides 2 encryption providers for encrypting the config file values.
- DataProtectionConfigurationProvider : It uses Windows DPAPIs(Data Protection API) to encrypt the data in config file and the key used to decrypt the encrypted values in stored in windows Local Security Authority (LSA).
- RSAProtectedConfigurationProvider : This provider uses public key encryption approach provided by RSACryptoProvider in .NET. This public key is stored in the config file itself.
To encrypt a configuration section use ConfigurationSection.SectionInformation.ProtectSection(providername) method and to decrypt the values use ConfigurationSection. SectionInformation.UnProtectSection() method.
Once you have encrypted the configuration sections, config file will no longer show the actual values instead it will be showing some cipher text. But at the time of accessing these values in code (C# or inline in aspx page) you don’t have to do anything like decrypting the config file or something, .NET will do it for you. But just take precaution while encrypting the config file values as this auto decryption done by .NET has some performance implications as well. So one should take a wise decision about which data to encrypt and which data can be written in plain text.
There are plethora of resources on this topic on web and my this post will also add to crowd, but following few link I found very informative and to the point.