Symmetric cryptography

The core idea of data encryption is the use of complex mathematical equations to encode (or cipher) data, which in effect will make this data unreadable to humans. In the world of secure software communication, the encrypted data can then be sent to the intended receiver, which will be expected to decrypt the data back to its original human-readable form.

In almost all cases, to encrypt a piece of data, you will need an encryption key. Encryption keys are simply a piece of the complex mathematical equations used to encode the data. In some encryption algorithms, you can use the same encryption key to decrypt your data back to its original form. In others, a decryption key that is different than the encryption key is needed to perform the decryption. 

Symmetric cryptography or symmetric-key algorithms are the algorithms that make use of the same key to encrypt and decrypt the data, which is why they are called symmetric. The following diagram shows where an encryption key is utilized to encrypt the word Hello into an encoded form, then the same key is used with the encoded data to decrypt it back to the word Hello.

Symmetric cryptography