In symmetric encryption, a shared secret is used to generate an encryption key. The same key is then used to encrypt and decrypt the data. This way of encrypting the data has been used for ages in various forms. It provides an easy way to encrypt and decrypt data, since the keys are identical. Symmetric encryption is simple and easier to implement, but it comes with the challenge of sharing the key with the users in a secure way.

Some examples of symmetric algorithms are as follows:

• Data Encryption Standard (DES): This algorithm uses the DEA cipher. DEA is a block cipher that uses a key size of 64 bits; 8 bits being for error detection and 56 bits for the actual key. Considering the computing power of today's computers, this encryption algorithm is easily breakable.
• Triple DES (3DES): This algorithm applies the DES algorithm three times to each block. It uses three, 56-bit keys.
• Advanced Encryption Standard (AES): This standard was first published in 1998, and it is considered to be more secure than other symmetric encryption algorithms. AES uses the Rijndael cipher, which was developed by two Belgian cryptographers, Joan Daemen and Vincent Rijmen. It replaces the DES algorithm. It can be configured to use a variable key size with a minimum size of 128 bits, up to a maximum size of 256 bits.
• Rivest Cipher 4 (RC4): RC4 is a widely used stream cipher, and it has a variable key size of 40 to 2,048 bits. RC4 has some design flaws that makes it susceptible to attacks, although such attacks may not be practical to perform and require a huge amount of computing power. RC4 has been widely used in the SSL/TLS protocol. Many organizations, however, have started to move to AES instead of RC4.