A humorous introduction to coding theory (the science behind cryptography), which traditionally features a character named Alice who tries to communicate with another character named Bob.
Against all odds, over a noisy telephone line, tapped by the tax authorities and the secret police, Alice will happily attempt, with someone she doesn't trust, whom she cannot hear clearly, and who is probably someone else, to fiddle her tax returns and to organise a coup d'etat, while at the same time minimising the cost of the phone call.
