A document created by the sender in his word processing application can be sent by electronic mail and thereby enable the recipient to make amendments to the identical text in his own word processing application, for example. It can also be sent over the growing informal network known as the Internet. All transactions conducted remotely are vulnerable to interception and forgery. Letters and documents are significantly more difficult to forge than their fax equivalents, which are in essence fairly poor quality photocopies. 7 Electronic mail within a private network is probably more difficult to intercept than over the public telephone network, but electronic mail over the public telephone network is as easy or difficult to intercept as fax or voice communications.
Electronic mail sent over the Internet is notoriously insecure and vulnerable to interception.
It is also highly vulnerable to forgery, since an electronic message has inevitably lost many of the characteristics of letters and even faxes that aid the detection of alterations or wholly bogus imitations. The solution to this problem has been found in developments in public key cryptography which took place in the 1970s and 1980s. The keys are associated mathematically, but the private key cannot practicably be derived from the public key. A message encrypted with the public key cannot be decrypted by that key, but only by the corresponding private key. He finds that X s public key is also required to decrypt it, from which it follows that X s private key must have been used to encrypt it, and that it could not have been altered since X encrypted it.