If you are using the ADO.NET SQL Server managed data provider and a SqlConnection object to connect to SQL Server, then you can enable encryption by adding the encrypt=true parameter to the connection string as shown here.

<configuration>
   <connectionStrings>
      <add name="MyDbConn"
       connectionString="Server=MyServer;Database=pubs;User Id=sa; password=database; encrypt=true"
       providerName="System.Data.SqlClient" />
     </connectionStrings>
</configuration>

Encryption is off by default.