## What is Cryptosystems?

A cryptosystem is a system that uses cryptographic techniques to provide Security services to users. The cryptosystem is also known as a Cipher system which means converting readable message format into a non-readable format. To understand the Cryptosystem in detail, let’s discuss a cryptosystem model that demonstrates how the sender and the receiver communicate secretly with each other.

In the above diagram, you can see the sender want to send a message to a receiver secretly, without revealing to any third party. to accomplish that cryptosystem comes into the picture. At the sender system, the cryptosystem takes the sender Message i. Plain text and using secret key (encryption key) it performs some encryption algorithm and forms a ciphertext and then sends it to the receiver. After receiving ciphertext at receiver side cryptosystem perform decryption algorithms using secret key (decryption key) and convert cipher text into plain text. The goal of the cryptosystem is to send private data from sender to receiver without interpretation of any third party.

### Components of Cryptosystem

Below is the list of Cryptosystem components:

- Plain text.
- Ciphertext.
- Encryption Algorithm.
- Decryption Algorithm.
- Encryption Key.
- Decryption Key.

#### 1)Plain text

The plain text is a message or data which can understand by anyone.

#### 2)Ciphertext

The ciphertext is a message or data which is not in a readable format, it is accomplished by performing the encryption algorithm on plain text using an encryption key.

#### 3)Encryption Algorithm

It is a process of converting plain text into Ciphertext using an encryption key. It takes two inputs i.e plain text and encryption key to produce ciphertext.

#### 4)Decryption Algorithm

It is an opposite process of an encryption algorithm, it converts cipher text into plain text using decryption key. It takes two inputs i.e ciphertext and decryption key to producing plain text.

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#### 5)Encryption Key

It is a key which sender used to convert plain text into cipher text.

#### 6)Decryption Key

It is a Key which the receiver uses to convert ciphertext into plain text.

### Types of Cryptosystems

There are two types of Cryptosystems – Symmetric Key encryption and Asymmetric key encryption. Let’s Discuss these two types in detail.

#### 1)Symmetric Key Encryption

- In symmetric key encryption, both the sender and the receiver use the same secret key i.e encryption key to perform encryption and decryption. Symmetric key encryption is also known as symmetric cryptography.
- There are some algorithms that use symmetric key concepts to achieve security. For example DES (Data Encryption Standard), IDEA (International Data Encryption Algorithm), 3DES (Triple Data Encryption Standard), Blowfish.
- Symmetric key encryption is mostly used by all cryptosystems
- In Symmetric-key encryption, the sender and receiver agree on the same secret key. the sender encrypts the private data i.e. plain text using a secret key and sends it to the receiver. After receiving data, the receiver uses the same secret key which is used by the sender to encrypt data. Using this secret key it converts cipher text into plain text.

In the below picture we can see the working of Symmetric key encryption.

**Features of cryptosystem in case of Symmetric-key encryption:-**

- As they use the same key for encryption and decryption, they have to share that secret key
- To prevent any type of attack secret key need to updated at regular interval of time.
- Length of the secret key in symmetric key encryption is small, hence the process of encryption and decryption is faster.
- There must be a mechanism to share a secret key between the sender and receiver.

**Challenges for symmetric key encryption-**

**Generating secret key:** To share Secret key both the sender and the receiver need to agree on the symmetric key which requires a key generation mechanism in place.

**Trust issue:** There must be trust between the sender and the receiver as they share the symmetric key. For eg suppose receiver lost his secret key to attackers, and he does not inform about this to the sender.

#### 2)Asymmetric key encryption

In asymmetric key encryption, two different keys are used by the sender and the receiver for encryption and decryption processes. Asymmetric key encryption is also known as the public key encryption.

In the above picture, we can see how the asymmetric key encryption works.

- In asymmetric key encryption, two keys are used. i.e. public key and private key. These two keys are related to each other in mathematics way. A public key is stored in a public repository and private keys are stored in a private repository.
- Using receiver public key sender encrypt the private data and send it to the receiver. After receiving private data, the receiver uses his private to decrypt private data.
- The length of keys in asymmetric key encryption is large, hence encryption and decryption processes in asymmetric key encryption becomes slow as compared to symmetric key encryption.
- Calculating the private key on the basis of the public key is computationally not so easy. As a result, public keys can be freely shared, allowing users to easily and conveniently encrypt content and verify digital signatures, and private keys can be kept the secret, making sure that content can be decrypted and digital signatures can only be created by private key owners. Asymmetric key cryptosystems face the challenge i.e. the user must be confident that the public key he is using for transmission with an individual is really that person’s public key and was not handled by an attacker.
- Also because public keys need to be shared but these public keys are large in size hence it is difficult to remember, so they are stored on digital certificates for secure transmission and sharing. While private keys cannot be shared, they are simply stored in the cloud software or operating system you are using, or on hardware devices. Many internet protocols like SSH, OpenPGP, SSL/TLS used in asymmetric cryptography for encryption and digital signature functions.

### Conclusion

In this article, we have seen how the cryptosystem helps to encrypt and decrypt messages securely and conveniently.

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