Like Microsoft's call for trustworthy computing, there are similarly a few inherent problems in communications between computers and/or between other electronic devices (such as for example Fax machines), which can initiate a similar call for trustworthy communications. These problems are caused mainly by various limitations in the currently employed communication protocols, for example over the Internet, or in Fax transmissions. The two main problems are: Verification by the sender that the user indeed received the message, and verification by the receiver that the purported sender indeed is the one who initiated the message. Both of these features are currently lacking for example in normal Fax communications and in normal email communications. In electronic communications over the Internet for example normal email communications allow users very easily to falsify the sender's email address, as happens for example many times when spam (unsolicited junk mail) is sent, or when various viruses, such as for example the Klez worm, spread themselves. A deeper issue in preventing the faking of email addresses is preventing the faking of IP addresses, since, clearly, making sure that the IP address is not forged can help considerably for verifying also the email address. Similarly, when sending normal email messages, the user cannot be sure that the receiver indeed received the message and/or if he/she opened it or read it. Although there are already some solutions to this 2.sup.nd problem, these solutions still have various remaining problems, so the problem has not been completely solved yet. The present invention solves the above problems by providing various solutions that preferably include improvement of the protocols and preferably include also methods for preventing theft of digital signatures.