# Cryptosystem Definition & Meaning

A cryptosystem is a suite of cryptographic algorithms needed to implement a particular security service, such as encryption. The term is a combination of *cryptographic system*, meaning a computer system that employs cryptography, which is a method of protecting information and communication through code so only the user for whom the information is intended can read it. The basic components of a cryptosystem include:

- Plaintext: the data needing the be protected during transmission
- Encryption algorithm: A mathematical process that uses an algorithm to transform information into meaningless ciphertext and requires the use of a key to transform the data back into its original form.
- Ciphertext: The scrambled version of the plaintext produced by the encryption algorithm using a specific encryption key.
- Decryption algorithm: A mathematical process that produces plaintext for any given ciphertext and decryption key. Ciphertext and a decryption key are the input, plaintext is the output.
- Encryption key: A value known to the sender. The sender inputs the encryption key into the encryption algorithm along with the plaintext to compute the ciphertext
- Decryption key: A value known to the receiver. It is related to the encryption key, but not always identical to it.The receiver inputs the decryption key into the decryption algorithm along with the ciphertext to compute the plaintext.

Cryptosystems are used for securely sending messages over the internet, such as credit card information or any other data that needs to be private. An *interceptor* is an unauthorized entity who attempts to determine the plaintext.

## Types of cryptosystems

There are two types of cryptosystems categorized by the method used to encrypt data:

**Symmetric key encryption**: An encryption system in which the sender and receiver of a message share a single, common key that is used to encrypt and decrypt the message.**Asymmetric key encryption**: An encryption system in which different keys are used for encryption and decryption with the keys being mathematically related. Each party has their own pair of keys exchanged during transmission.

The diagram below shows the cryptosystem process that occurs when a sender wants to send a message to a receiver secretly.

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