validationKey = CreateKey(20); 

decryptionKey = CreateKey(24); 

protected string CreateKey(int len) 

     { 

byte[] bytes = new byte[len]; 

new RNGCryptoServiceProvider().GetBytes(bytes); 

              StringBuilder sb = new StringBuilder(); 

for(int i = 0; i < bytes.Length; i++) 

              {    

                   sb.Append(string.Format("{0:X2}",bytes[i])); 

              } 

return sb.ToString(); 

     } 

xml version="1.0"?> 

<configuration> 

<system.web> 

<machineKey validationKey="3FF1E929BC0534950B0920A7B59FA698BD02DFE8" decryptionKey="280450BB36319B474C996B506A95AEDF9B51211B1D2B7A77" decryption="3DES" validation="SHA1"/> 

system.web> 

configuration>