In order to be able to exchange information confidentially, various encryption methods are used. They all have one goal: to make messages illegible for unauthorized persons and also to ensure the confidentiality (access protection), the integrity (change protection) and the authenticity (protection against forgery) of the information. For this purpose, the message is transferred from a readable state to a seemingly meaningless string.
- The encryption is used for the confidential exchange of information.
- RSA encryption was developed in 1977 and consists of a public key and a secret key.
- The various locks can only be opened with a single key – which is in the possession of the recipient.
From antiquity to the present – the secret key procedure
The idea of encrypting messages goes back to the Old Kingdom of Egypt. In the Middle Ages, for example, diplomatic correspondence should be protected from espionage. For example, secret messages were sent in which the meaning of the letters was changed. An A became a D, a B became an X, and so on. Only those who knew the alphabetical relationships – that is, in possession of the key – could read the message correctly. This was a so-called symmetrical encryption, whereby the same key was used for both encryption and decryption.
But all symmetrical encryption methods from antiquity through World War II to the 1970s had one problem in common. How does the key reach the recipient? Because in addition to the message, the key must also be handed over to the recipient in a suitable manner (e.g. via a confidential messenger). It must neither be intercepted nor manipulated on its way.
In the age of electronic communication, this fact is very disadvantageous because spontaneous, encrypted communication is not possible in this way. In this case, spontaneous means that the communication partner is neither known personally nor is in the immediate vicinity.
Public key procedure: Lots of padlocks and only one key
For this reason, the scientists Whitfield Diffie and Martin Hellman developed a revolutionary process in the 1970s that made this key exchange superfluous – the so-called public key process (also: two-key system). The mathematical formulas for practical application were added a short time later by the American scientists Ronald Rivest, Adi Shamir and Leonard Adleman. The initials of their surnames gave the process its name: RSA encryption.
The asymmetric RSA encryption consists of a public (public key) and a secret (private key) key. But how exactly do you have to imagine that? Figuratively speaking, the message recipient has an infinite number of padlocks. All of these locks can only be opened with a single key – which is in the possession of the recipient. In order to give others the opportunity to transmit encrypted messages, they hand out a padlock to anyone who wants to. The sender of the message takes the lock and uses it to lock the message. Since only the recipient has the only matching key, the message can neither be changed nor opened on its way.
The padlock corresponds to the public key used to encrypt the message. The private key corresponds to the key that is used to decrypt the message. With this method one of the fundamental problems of cryptography was overcome – the key exchange.