Problem

But there is a problem. What shall Bob do, if he does not receive enough packages to restore the whole message? What if packages get lost? What if there is no package for a serial number, which is recognized as grain? If only one of the packages 2,3,6 or 8 get lost, the message will be incomplete. This could happen by errors on the communication link. So we create a new design:

1. Read an incoming package.
2. Calculate the MAC, if it is ok, then add the message to the plaintext.
3. Do the upper loop with the next package, until all packages were processed.
4. Are there serial numbers left? Rerequest all missing serial numbers, where no correct package was found.