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Understanding User Account Control (UAC)

A. For IPSec (tunnel mode or transport mode) to negotiate encryption, the systems must first decide they are willing to trust each other. There are two methods defined in IPSec to accomplish this. One is with X.509 certificates and the other is with preshared keys. The most secure way to do this is with X.509 certificates. In this case, the two systems first obtain an X.509 certificate from certificate authorities so that the certificates share a common root authority. Think of it as both sides getting the certificate from someone they mutually trust. In this case, the certificate for the gateway uniquely identifies the gateway, and the certificate for the client uniquely identifies the client. Using IKE, the certificates are securely exchanged and the gateway and the client computers can authenticate each other after they generate encryption keys and begin using the IPSec main mode security association (SA). Because certificate deployment had not yet matured, preshared keys were primarily placed into the IPSec standard for the purpose of testing basic interoperability between vendor implementations. Some people continue to use preshared keys rather than deploy much more secure X.509 certificates. For preshared keys, each operating system is configured with a shared key (similar to a password). When the operating systems start IPSec main mode negotiation using IKE, they indicate to each other that a preshared key is used as the authentication method. However, there is no way to uniquely identify the gateway or the client in advance (particularly in remote access). You might try using the IP addresses as a hint, but in remote access, there is no way to uniquely identify the gateway or client in

Circle c = new Circle(10);

help you learn about the kinds of errors you are 2 personally prone to, see A 3 Discipline for Software 4 Engineering (Humphrey 1995).

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<configuration> <connectionStrings> <add name="Local_Northwind connectionString="SERVER= ;DATABASE= ;UID= ; /> </connectionString> <system.web> <caching> <sqlCacheDependency enabled="true pollTime="60000 > <databases> <add name="Northwind connectionName="Local_Northwind /> </databases> </sqlCacheDependency> </caching> </system.web> </configuration>

You can define extension methods for delegate types, too . For an example of this, turn to page 278 in 11, Events . You can also add extension methods to enumerated types . I show an example of this in the Adding Methods to Enumerated Types section in 15, Enumerated Types and Bit Flags . And last but not least, I want to point out that the C# compiler allows you to create a delegate (see 17, Delegates, for more information) that refers to an extension method over an object:

The Mutex class can be used to provide synchronization between processes. Here's a simple example of using the Mutex class: