Microsoft released a security-design performance comparison article that applies to SQL Server 2000, Windows 2000 Advanced Server, ASP.NET, and the .NET Framework. The article compares the relative performance of various security options available for client authentication, hashing algorithms, cryptography techniques, and digital signatures. Usually, the more secure your system is, the more you've compromised performance and usability. Read the Microsoft article "Performance Comparison: Security Design Choices" at

http://msdn.microsoft.com/security/securecode/dotnet/default.aspx?pull=/library/en-us/dnbda/html/bdadotnetarch15.asp