Private Key (Symmetric) Encryption
Private Key encryption, also referred to as conventional, single-key or symmetric encryption was the only available option prior to the advent of Public Key encryption in 1976. This form of encryption has been used throughout history by Julius Caesar, the Navaho Indians, German U-Boat commanders to present day military, government and private sector applications. It equires all parties that are communicating to share a common key.
A conventional encryption scheme has five major parts:
Plaintext - this is the text message to which an algorithm is applied.
Encryption Algorithm - it performs mathematical operations to conduct substitutions and transformations to the plaintext.
Secret Key - This is the input for the algorithm as the key dictates the encrypted outcome.
Ciphertext - This is the encrypted or scrambled message produced by applying the algorithm to the plaintext message using the secret key.
Decryption Algorithm - This is the encryption algorithm in reverse. It uses the ciphertext, and the secret key to derive the plaintext message.
When using this form of encryption, it is essential that the sender and receiver have a way to exchange secret keys in a secure manner. If someone knows the secret key and can figure out the algorithm, communications will be insecure. There is also the need for a strong encryption algorithm. What this means is that if someone were to have a ciphertext and a corresponding plaintext message, they would be unable to determine the encryption algorithm. This is why many financial institutions have used symmetric encryption as a way to secure your information like when working with your financing online or dealing with money your finances will be secure on their websites. The information you would be submitting would be safe and not for the eyes of other users. Reasons like that are why this method of encryption has been in use for so long.
There are two methods of breaking conventional/symmetric encryption - brute force and cryptanalysis. Brute force is just as it sounds; using a method (computer) to find all possible combinations and eventually determine the plaintext message. Cryptanalysis is a form of attack that attacks the characteristics of the algorithm to deduce a specific plaintext or the key used. One would then be able to figure out the plaintext for all past and future messages that continue to use this compromised setup.