Just looking through my notes about RSA digital signature, and I dont understand what this means:

ALICE has public key

BOB has public key

Alice wishes to send to sign and send Bob the message M which is on a single block. We are also assuming that . Incase , Alice must invert the order she carries out her 2 calculations that follow and Bob must do the same.

Alice calculates:

Alice sends Bob C.

I'm not exactly sure what it means byAlice must invert the order she carries out her 2 calculations that follow. Does this mean I just do them in reverse order, or do the M, C and S values swap round but the d and e values stay the same? Because if it just means swapping the order then I'll be left with S...but then Alice is meant to send C....very confused!

Please could anyone explain this?

Thanks in advance!