Symmetric Cipher

Symmetric Ciphers
Functions Provided: Encryption and Decryption.

They are known as Symmetric because both the sender and the receiver share the same key to encrypt and then decrypt the data. The main function is to provide Confidentiality.
e.g. Say Alice needs to send Bob a confidential document. She would encrypt the document using a symmetric cipher and a key and send it to Bob. Anybody looking at the message enroute to Bob will only see sequence of bytes. Bob on receiving the message will use the same key and the decrypt function of the symmetric cipher used by Alice to produce the original message. Few Symmetric Ciphers are: rotate cipher, Caeser cipher etc.

Disadvantages:
1. The key has to transferred to Bob through a separate communication channel which has to be secure. Then the question arises, if we have a secure communication channel, then why not send the document through that secure channel.
2. If Alice needs to send the document to 100 people, then she would have to use 100 different keys and encrypt the message 100 times and share them across.