privacy and cryptography

The first person who used cryptography was Julius Caesar! He had to sent messages but he didn't trust the messengers, so he invented a method of disguising those messages. Only the intended recipient - who knew the right method to make the message readable - could read through the disguise. So, what's cryptography? Well, cryptography is the art of creating and using cryptosystems. A cryptosystem, is a method of disguising messages, so that only intended recipient can read them. Cryptosystems are also called cipher systems. The art of breaking cryptosystems is called cryptoanalysis. Well, the science which study cryptography and cryptoanalysis is called cryptology (from the Greek kryptos logos, meaning 'hidden 'word').The original message is called plaintext, and the disguised message is called ciphertext. When you disguise a message, you are using a procedure to convert it into a ciphertext. This procedure is called encryption. Vice versa, when you want to make the message readable, you use an opposite procedure called decryption. Why am I talking about cryptography here? Well, because there are many reasons to encrypt messages which travel on the net. Just as a sample, you could send personal information to someone, say your credit card number, and, obviously, you would like to avoid that someone - who isn't the intended recipient - can read your information. Maybe you are now wondering about how someone can read your mail...Ok, look at the header area of any e-mail message. Done? Well, as you can see, it has passed through several hosts on its way to you. Now, please, think about your e-mail messages as they were postcards...Ok, now just consider that any person who work at these hosts can read your postcards! Incredible: snail mail is more secure than e-mail! Well, at least you can put your letters inside an envelope to hide from casual snooping...I don't think you send all your mail by means of postcards! Hence, the importance of cryptography on the net.