It has to be admitted that information technology (computers and networks, a domain completely intertwined with telecommunications in this day and age) can, in some cases, cause privacy problems.  For example, the simple sending of an e-mail is as public as sending a postcard.  So the question is: is there a safe way to communicate, away from the prying eyes of interceptors or hackers who get into our computers to install who knows what and look at all our files?  There are some solutions, even though they are not yet in common use.

Cryptography is a technique which allows you to hide the content of any message; it has been around for thousands of years and has often been used for military purposes.  One of the simplest methods is attributed to Julius Caesar, who used it for his private correspondence.

The technique consists in replacing every single letter of the original message with the letter that comes 3 places further along in the alphabet (so all the As are replaced with Ds, the Bs with Es, the Cs with Fs, etc), so as to make the message unintelligible.  Obviously, techniques have developed over the centuries. One of the techniques used is DES (Data Encryption Standard) which foresees the use of the same key, which is secret and known only to the sender and the receiver, to cypher and decypher the message.  This is called "symetric key" cryptology.  The problem is how to agree on the same secret code, which must somehow be transmitted safely.

To get round this problem, a different type of algorithm has been developed, called RSA (after its inventors’ initials) This technique is called "public key" and uses two keys – one for crypting and the other for decrypting, but only one of the two keys must be kept secret.  RSA makes use of the particular mathematical properties of prime numbers which make decyphering the message almost impossible because there are no known algorithms capable of easily factorising a number (this operation is necessary in order to make the message comprehensible again). Often, DES and RSA are used together.

These methods can be used to solve problems of authentication (confirmation of the other party’s identity during on-line communication) and message integrity (the guarantee that what you have received has not been tampered with during transmission), using "digital fingerprinting and certification", i.e. the equivalent in the electronic world of our signatures and ID cards.

Thanks to the use of these techniques we can safeguard communications established with electronic commercial sites when we buy on-line; we can also make electronic mail safer by using  PGP ("Pretty Good Privacy"), a widely-used programme available on-line, which makes use of RSA.