@book { ZahlungssystemeimInternet,
    title = "Zahlungssysteme im Internet",
    author = "Christian {Strenge}",
    year = "2001",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832440176",
    url = "https://m.diplom.de/document/219652"
}