i found an difficulties when Encryption and Decryption for Richtextbox data.
I am developing an application project regarding educational software. In one form i am displaying one Richtextbox for saving the question in sqlserver. while savig i am decrypt it and save now when fetching the value from db i have an problem.
My problem is when the question contains the (threfore symbol  while decrypting the such line whole line in the form of symbol.
no problem with image/mathtype/text.
I am used 4 to 5 symmetric algorithm for that solution but its still not working.

Can anybody help me.

i am attaching the image file understanding

Need to see some code and database field descriptions/types