RSA Blind attack help
Here is what should be done:


After getting the blinded message M' You should convert it back to string format. (First to hex, then string)
You should convert this m' to base64 like you did.
Send this base64 encoded message to client like you did.


The rest of the solution looks okay. 

P.S: There is still a defect in that solution that i can not find.