Symmetric Encryption

In this tutorial, we are going to see What is Symmetric Encryption in Computer Security?

Symmetric encryption (also called private key encryption or secret key encryption) involves using the same key for both encryption and decryption.
 

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Encryption consists in applying an operation (algorithm) on the data to be encrypted with the help of the private key, in order to make them unintelligible. Thus, the slightest algorithm (such as an exclusive OR) can make the system almost unbreakable (absolute security does not exist).

However, in the 1940s, Claude Shannon demonstrated that to be totally secure, private key systems must use keys of a length at least equal to that of the message to be encrypted. Moreover, symmetric encryption requires a secure channel for the exchange of the key, which seriously degrades the interest of such an encryption system.

The main disadvantage of a secret key cryptosystem comes from the exchange of keys. In fact, symmetric encryption relies on the exchange of a secret (the keys). Thus, the problem of key distribution arises.

On the other hand, a user wishing to communicate with several people while ensuring distinct levels of confidentiality must use as many private keys as he has people to communicate with. For a group of N people using a secret key cryptosystem, it is necessary to distribute a number of keys equal to :
N * (N-1) / 2.
 

 
Thus, in the 1920s, Gilbert Vernam and Joseph Mauborgne developed the One Time Pad method (sometimes called “One Time Password” and noted OTP), based on a private key, randomly generated, used once and only once, then destroyed. At the same time, the Kremlin and the White House were connected by the famous red telephone, which is a telephone whose communications were encrypted with a private key using the one-time password method. The private key was then exchanged through the diplomatic bag (acting as a secure channel).
 
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