Symmetric encryption is a data encryption technique characterized by the sender and recipient sharing the same encryption key, which is used to both encrypt and decrypt the message being sent.

Symmetric Encryption Algorithms

Among the various symmetric encryption algorithms currently in use, we can mention DES (Data Encryption Standard), 3-DES, AES (Advanced Encryption Standard), and IDEA (International Data Encryption Algorithm).

DES is perhaps the best-known symmetric encryption algorithm, but its use is currently strongly discouraged because its vulnerability was demonstrated in 1998, when a message encrypted with this algorithm was broken. The DES algorithm has a key length of 64 bits, of which 8 are control bits and do not affect the encryption process. This results in a key space of 2⁵⁶, which, although it seemed enormous when the algorithm was first conceived, has become manageable with modern computer developments. An attempt to make DES more secure is the 3-DES algorithm, in which the DES algorithm is applied three times to a given message, resulting in a triple key length.

The other symmetric encryption algorithms we mention, namely AES and IDEA, have the characteristic of having an encryption key of at least 128 bits and are therefore more secure. In fact, the security of symmetric encryption algorithms depends primarily on the length of the key: the more bits the key has, the more difficult it is to break it with a brute-force attack, i.e., an attack that explores all possible combinations.

Advantages and Disadvantages

Symmetric encryption algorithms have the enormous advantage of being very efficient in creating encrypted messages from even very large plaintext messages.

The major problem with symmetric encryption, however, is key distribution: if two users want to communicate securely, they must first exchange the key securely, for example, by meeting in person away from prying eyes. Obviously, this problem is difficult to solve when communicating over computer networks: an insecure channel cannot be used to transmit the key, since it can potentially be compromised. compromise the entire secret communication. Furthermore, the continuous use of the same key still exposes it to risks over time, also due to technological evolution (see the DES case).

The problem of secure key exchange was only overcome in the 1970s with the invention of asymmetric cryptography.