Data protection is often achieved using so-called symmetric cipher. Usage of a symmetric cipher is very straightforward. The only things that both parties need is a common key and a common cipher (algorithm). The common key must be kept secret from any third party. It can be, for example, a chosen passphrase.
Sender: key + cipher + message -------------------> encrypted message.
The encrypted message is a string of chaotic characters, which does not give sense. Without knowledge of the key, it is impossible to find the original message from the encrypted message in reasonable time (say, less than millions of years). Therefore, the encrypted message can be sent over the Internet or by a SMS, without need to worry about eavesdropping. Even if adversaries intercept the encrypted message, they cannot find the meaning.
A typical encrypted message
Receiver: key + cipher + encrypted message -----------------------> original message.
„A symmetric cipher“ is a general term, just like „car“. There are many car types, and there are many types of symmetric ciphers. These ciphers differ by their quality. Some of the ciphers were shown to be weak (e.g. FEAL), some have become obsolete (e.g. DES). The best class of ciphers consists of ciphers which are known for many years, and yet they still resist scientific attacks trying to compromise them. Such ciphers are, for example, AES, Blowfish and IDEA.
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