Encrypt & Decrypt Strings in Silverlight

<?xml version="1.0"?>
<configuration>
  <configSections>
    <sectionGroup name="system.serviceModel">
      <section name="domainServices" type="System.ServiceModel.DomainServices.Hosting.DomainServicesSection, System.ServiceModel.DomainServices.Hosting, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" allowDefinition="MachineToApplication" requirePermission="false" />
    </sectionGroup>
  </configSections>

  <connectionStrings>
    <add name="ApplicationServices"
         connectionString="data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|\aspnetdb.mdf;User Instance=true"
         providerName="System.Data.SqlClient" />
  </connectionStrings>

  <system.web>
    <httpModules>
      <add name="DomainServiceModule" type="System.ServiceModel.DomainServices.Hosting.DomainServiceHttpModule, System.ServiceModel.DomainServices.Hosting, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
    </httpModules>
    <compilation debug="true" targetFramework="4.0" />
    <globalization culture="auto" uiCulture="auto" />

    <authentication mode="Forms">
      <forms name=".Encrypt_Decrypt_SBA_ASPXAUTH" timeout="2880" />
    </authentication>

    <membership>
      <providers>
        <clear/>
        <add name="AspNetSqlMembershipProvider" type="System.Web.Security.SqlMembershipProvider" connectionStringName="ApplicationServices"
             enablePasswordRetrieval="false" enablePasswordReset="true" requiresQuestionAndAnswer="false" requiresUniqueEmail="false"
             maxInvalidPasswordAttempts="5" minRequiredPasswordLength="6" minRequiredNonalphanumericCharacters="0" passwordAttemptWindow="10"
             applicationName="/" />
      </providers>
    </membership>

    <roleManager enabled="true">
      <providers>
        <clear/>
        <add name="AspNetSqlRoleProvider" type="System.Web.Security.SqlRoleProvider" connectionStringName="ApplicationServices" applicationName="/" />
        <add name="AspNetWindowsTokenRoleProvider" type="System.Web.Security.WindowsTokenRoleProvider" applicationName="/" />
      </providers>
    </roleManager>

    <profile>
      <providers>
        <clear/>
        <add name="AspNetSqlProfileProvider" type="System.Web.Profile.SqlProfileProvider" connectionStringName="ApplicationServices" applicationName="/"/>
      </providers>
      <properties>
        <add name="FriendlyName"/>
      </properties>
    </profile>

  </system.web>

  <system.webServer>
    <validation validateIntegratedModeConfiguration="false"/>
    <modules runAllManagedModulesForAllRequests="true">
      <add name="DomainServiceModule" preCondition="managedHandler"
          type="System.ServiceModel.DomainServices.Hosting.DomainServiceHttpModule, System.ServiceModel.DomainServices.Hosting, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
    </modules>
  </system.webServer>

  <system.serviceModel>
    <behaviors>
      <serviceBehaviors>
        <behavior name="">
          <serviceMetadata httpGetEnabled="true" />
          <serviceDebug includeExceptionDetailInFaults="false" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <bindings>
      <customBinding>
        <binding name="Encrypt_Decrypt_SBA.Web.Services.ServiceTest.customBinding0">
          <binaryMessageEncoding />
          <httpTransport />
        </binding>
      </customBinding>
    </bindings>
    <services>
      <service name="Encrypt_Decrypt_SBA.Web.Services.ServiceTest">
        <endpoint address="" binding="customBinding" bindingConfiguration="Encrypt_Decrypt_SBA.Web.Services.ServiceTest.customBinding0"
          contract="Encrypt_Decrypt_SBA.Web.Services.ServiceTest" />
        <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange" />
      </service>
    </services>
    <serviceHostingEnvironment aspNetCompatibilityEnabled="true"
      multipleSiteBindingsEnabled="true" />
  </system.serviceModel>
</configuration>