SecuredConfig.Core

This project is mainly for extending .NET Core Configuration to support mixed encrypted configuration values.

Introduction

In .NET Core, there is no built-in configuration protection or encryption offically provided from Microsoft. Therefore, several configuration encryption libraries were developed from communities. However, most of those configuration encryption libraries only support field level or file level content encryption, but not partial content in a configuration value. For example, a Connection String usually looks like this Data Source=(local);Initial Catalog=MyDB;User ID=sa;Password=mysecret. Most of the time we just want to protect the credential (e.g. the password mysecret from above example), we still want to keep other informations like the data source and DB name visible for better troubleshooting, but most of those libraries will encrypt the whole connection string. In case we just want to check whether the DB server is pointed to correctly or not, we still need to decrypt the whole connection string. That's why this library was created in order to support partial encryption over configuration values from any ConfigurationSource (e.g. appsettings.json, Environment varibles, etc.), and it will not affect your configuration utilization since it's basically transparent to your program.

Prepare your PFX certificate with private key

The PFX certificate can be created by self signed or issued by a trusted CA (recommended for production). Here is an example to generate PFX certificate with private key using Openssl:

openssl genrsa 2048 > private.key

openssl req -new -x509 -nodes -sha256 -days 365 -key private.key > public.cer

openssl pkcs12 -export -in public.cer -inkey private.key -out cert.pfx

Encrypt the secret string using Command line tool

To install the SecuredConfig CLI, just execute dotnet tool install -g SecuredConfig.Cli. After that you can use it with the command secured-config from your command line.

To encrypt your secret value like "mysecret", just execute:

secured-config encrypt --cert public.cer -s "mysecret"

The encrypted value will be output like this: {Enc:CN=dummy,NotAfter=2033-04-25:3IAyMsx49Y7+rYLQONt+0w7tzleJdRQ5XDRIEuHJbKQoJM6U18t6eCQ9ECT0DzlW5hsqnqGDIUB0Udw8QYjhfc4yL03xY8oLYwRc6UP5T+3YyTuNsxNFxgSwtd0MIYt7NxZuDM/5mNzM9d5FxnnnpV/yz2FLtIbMV6gcwuKwa/ZP9fjSZAzWe3tajDYIBHOfq69UoQxl3ibV9a2dToqV0AG1t+qNGHJY4leiBauzElVEvrwhsGySD/PryVVXxnVwRq1rKWMbwoj7PqDnZ5ypefmqO2oY+zdwcKv6jIoZriUddAGni9VWkTDyZwVnrR9Rz1iR8Azm0QoywKfL5bQItQ==}

Copy the encrypted value and replace your plain text mysecret in appsettings.json or environment variables.

Certificate setup for decryption

Add PFX Certificate to your LocalMachine or CurrentUser's Personal Store

1. Double click your .pfx file, Select Current User and click Next button twice.

2. Enter the password"

3. Select "Place all certificates in the following store" and Click "Browse" to select "Personal" store.

4. Click "Next" and then "Finish" button

Add PFX Certificate in Linux (if application to run on Linux)

1. Login as (or su <svc_account>) the target service account
2. Run below commands and input the input pfx password:

mkdir -p ~/.dotnet/corefx/cryptography/x509stores/my/
openssl pkcs12 -in cert.pfx -nodes | openssl pkcs12 -export -passout pass: -out ~/.dotnet/corefx/cryptography/x509stores/my/cert.pfx

.NET Core Integration with transparent decryption

Install the nuget package SecuredConfig.Core

dotnet add package SecuredConfig.Core

Modify your application to support transparent decryption

Just add .UseSecuredConfiguration() after Host.CreateDefaultBuilder(args). If you have customized configurations other than .NET Core defaults, please place .UseSecuredConfiguration() after .ConfigureAppConfiguration(...) in order to overlay all the configuration sources.

Example:

public class Program
{
    public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .UseSecuredConfiguration()  // <-- add this line
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });
}

.NET 6 Example:

var builder = WebApplication.CreateBuilder(args);

builder.Host.UseSecuredConfiguration();  // <-- add this line
builder.Services.Addxxxx();
...

var app = builder.Build();
app.UseRouting();
...
app.Run();

The corresponding appsettings.json may look like:

{
  "ConnectionStrings": {
    "Default": "Data Source=DBServer;Initial Catalog=Test;Password={Enc:CN=dummy,NotAfter=2033-04-25:vaAO17L+53RUA51Fhxo9Cg==};User ID=dev;",
  },
  "Logging": {
    "LogLevel": {
      "Default": "Debug",
      "System": "Information",
      "Microsoft": "Information"
    }
  }
}

• {Enc:[cert title]:xxxxxxxxxxxxxxxxxxxxxxxxxxxx} is the encrypted pattern. Where "xxxxxxxxxxxxxxxxxxxxxxxxxxxx" is the RSA public key encrypted Base64 string and [cert title] will be used to search in Cert Store.

Later on when your code try to access Configuration["ConnectionStrings:Default"], it will retrieve the Decrypted value automatically.

Production Remarks

• Consider to install the Certificate into "Local Machine" instead of "Current User" to support different service accounts to access the certificate.
• Make sure the application service account has permission to read the Certificate's Private key.
• If the certificate can be found in LocalMachine, it will not search in CurrentUser

Environment Variables

You can specify below Environment variables to override the default Certificate Store

CRYPTO_CERTIFICATE_STORE

The certificate store to lookup. Default is "My" (Personal store)

How it works

Overlay.SecuredConfigurationProvider

Extend ConfigurationProvider and reference the concepts from ChainedConfigurationProvider to create an overlayed configuration to wrap the given IConfiguration (usually built from ConfigurationBuilder) and use regular express to detect whether there is encrypted value pattern then apply auto decryption over the underlying configurations.

You just need to add .UseSecuredConfiguration() to IHostBuilder during Main Program startup. It will be transparent to all the configuration consumers.