How can a user send a sensitive message so that it remains secure from prying eyes? If you send a letter, it could be intercepted, opened, read and then closed without leaving a trace. A telephone call can be wiretapped.
Rapid development of cryptography started in 20th century together with development of computing technologies. Computers allowed not only much faster encryption of electronic messages, but also much faster cracking of encryption keys used so far.
Encryption is not a silver bullet and doesn’t guarantee total confidentiality. A frequent technique to bypass encryption is to capture the message before it even gets encrypted – for example by a stealth Trojan horse program installed on sender’s computer that will monitor all keys pressed on the keyboard or even in the victim’s mobile telephone.
Another attribute you almost always need to protect when encrypting a message is its integrity (i.e. the completeness of the file) – otherwise the message can be manipulated, without even knowing the encryption key. Most respected encryption tools will do that for you automatically.
The following image demonstrates the stages of public key encryption – this works on the basis of a pair of keys – one public and one private:
1.The sender requests a copy of this public key.
2.Using the appropriate software, the sender encrypts the message using the recipient’s public key.
3.The message is sent.