Causes, Solutions, and Best Practices

introduction

When working with ASP.NET Core, you may encounter warnings related to data protection. These warnings often appear in the stdout log and can be confusing. Understanding these warnings is important to ensure the security and stability of your application, especially in a production environment.

This article describes common data protection warnings that occur in ASP.NET Core and provides solutions to identify and resolve their causes.

problem
Enable stdout logging by setting the stdoutLogEnabled property to true in your web.config file. Here’s the full configuration for how to enable it in an ASP.NET Core application.

You may see warnings similar to the following in the stdout log when an application is terminated or an application pool is stopped or recycled:

warn: Microsoft.AspNetCore.DataProtection.Repositories.EphemeralXmlRepository[50]
      Using an in-memory repository. Keys will not be persisted to storage.
warn: Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager[59]
      Neither user profile nor HKLM registry available. Using an ephemeral key repository. Protected data will be unavailable when application exits.
warn: Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager[35]
      No XML encryptor configured. Key {0cd9f297-xxxx-xxxx-xxxx-xxxxxxxx59ac} may be persisted to storage in unencrypted form.

This warning indicates that your application is using in-memory data protection storage. This setting can have significant implications on data security and application stability, especially when deployed to production environments.

cause

The warning occurs because the application uses in-memory storage for data protection keys. These keys are temporary and will be lost if the application is stopped or restarted. This also causes existing cookies on the client browser to no longer be available, requiring the server to send new cookies.

Solution
To address these concerns and ensure that your application’s data protection mechanisms are secure and persistent, you can configure a persistent store to prevent encryption key loss when your application restarts. This can be a file system directory, a cloud-based storage service such as Azure Key Vault, or a database.

PersistKeysToFileSystem

builder.Services.AddDataProtection()
        .PersistKeysToFileSystem(new DirectoryInfo(@"C:\keys\"))
        .ProtectKeysWithDpapi(); // Encrypt keys using Windows DPAPI

This snippet stores the key in the C:\Keys folder. It encrypts the key using DPAPI. DPAPI encryption requires user profile information, updates the application pool, and sets the user profile property to True.

ProtectKeysWithAzureKeyVault

builder.Services.AddDataProtection()
    .PersistKeysToAzureBlobStorage(new Uri(""))
    .ProtectKeysWithAzureKeyVault(new Uri(""), new DefaultAzureCredential());

PersistKeysToDbContext

builder.Services.AddDataProtection()
    .PersistKeysToDbContext();

conclusion

Warnings related to ASP.NET Core’s data protection system are important indicators that your application may not be handling encryption keys securely. Configuring persistent storage and implementing encryption ensures that your application’s data protection mechanisms are strong and secure. To learn more about ASP.NET Core data protection, visit this link.Configuring ASP.NET Core Data Protection | Microsoft Learn