# Symmetric Key Encryption

Introduction: – Till now you have learned about the basic meaning and the motive behind cryptography and the various means of encrypting information. There are more to learn about encryption system. Encoding of plain text is done in two ways and the name is given based on the keys used in encryption. These are: –

• Symmetric key encryption and
• Asymmetric key encryption

In this chapter you will learn about the symmetric key encryption. In this type of cryptography, encoding of plain text is done by mangling or merging it with secret key. For that reason, at the time of decryption the same knowledge of key is required. The formula looks something like this-

cipher-text = encrypt( plain-text, key )
plain-text = decrypt( cipher-text, key )

This is a diagram of how symmetric key encryption works with single key, which remains secret. This very same key is used for both encrypting and decrypting the plain text as well as cipher text.

Scenario to use this Encryption Technique: –
This type of cryptographic technique becomes useful when you want to encrypt your own files in your personal drive / system and want to decrypt it as per requirement. This will help you keep your file safe and unreadable. But this very technique becomes less useful when you sent them to someone else as a secret message and want that other guy to decrypt it. The problem will arise in key distribution and hence this problem is named as “key distribution
problem”

Example of Such algorithm: –
The very simple example of symmetric key algorithm is the Caesar cipher, developed by Julius Caesar who started this technique by shifting 3 letters up for every plain text within that set of information. This 3 letter up became the key for encryption. You might have gone through this topic in your previous chapter.

DES (Data Encryption Standard): –
This was the standard form of encryption till about the year 2000 from 1977 and is globally used algorithm. This is also an example of symmetric key encryption. DES was developed in the year 1975 and was standardised by the American National Standard Institute in 1981. It uses a 56 bit key and uses block cipher technique that gets  converted to 64 bit blocks and then encrypts the information.

There was another strong algorithm for encryption which was slower than DES but stronger. This was the 3DES. As the name says, it uses the technique of tripling the key length of standard DES to the size of 168-bits, which makes this algorithm more strong and secure, but was comparatively slower.