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Table of contents
Introduction to Cryptosystems
Components of Cryptosystems
Types of Cryptosystems 
Symmetric Key Cryptosystems 
Asymmetric Key Cryptosystems
Challenges Faced
Symmetric Key Encryption 
Asymmetric Key Encryption
Cryptosystem Attacks 
Kerckhoff's Principle
Frequently Asked Questions
What are Cryptosystems?
What is meant by symmetric key encryption?
What does asymmetric key encryption mean?
What is Kerckhoffs's principle?
Where can we use Cryptosystems?
Last Updated: Mar 27, 2024

What Do You Mean by Cryptosystem?

Author Ayushi Goyal
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Ashwin Goyal
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The Internet is a widely used and foremost important tool used by almost everyone worldwide. It helps in interchanging information between the sender and receiver. But, with the increase in cyber crimes, we need to protect the data from unauthorized access. Cryptosystems or Cryptographic systems are used for this purpose. 


In this article, we will discuss what cryptosystems are. We will also see various components and types of cryptosystems available. Furthermore, we will discuss the challenges faced by each of these systems. At last, we will be studying various cryptosystem attacks and Kerckhoff's principle. 

Introduction to Cryptosystems

Cryptosystems are computer systems that are also known as cryptographic or cipher systems. In cryptography, a cryptosystem is a set of algorithms used to encode and decode messages. These systems provide various methods for protecting information and secure communication. These systems use codes for encoding the message so that only the intended audience can read and understand it. 

Cryptosystems use keys as input for cryptographic activities to perform operations on the plaintext. The system's security depends on the level of security of these keys. The below illustration describes a simple model of cryptosystems. 


In this illustration, the sender creates a message for the receiver. To send this message confidentially, cryptosystems are used. The model uses the encryption algorithm of the system to encrypt the message using a secret key. A ciphertext is produced after performing operations on the message using the key. This ciphertext is then sent to the receiver. Now decryption algorithm came into use for converting the ciphertext back to the original message. 

To make all the algorithms and operations work efficiently. Cryptosystems contain several components. Let's discuss the components of cryptosystems. 

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Components of Cryptosystems

A basic cryptosystem contains the following component:

  • Plaintext - It is a readable text generated by the sender. It is given as an input to the encryption algorithm.
  • Encryption Algorithm - It is a method provided by the cryptosystem. This algorithm generates an encryption key and converts the plain text into cipher text using that key. 
  • Encryption Key - It is a random bit set used to encrypt plaintext into cipher text. The value of this encryption key is known to the sender.
  • Ciphertext - Unlike plaintext, the ciphertext is unreadable. It is encrypted from plaintext. The encryption algorithm outputs ciphertext using plaintext and key. 
  • Decryption Algorithm - This algorithm takes the encrypted text and the original message. 
  • Decryption Key - It is also a random bit set used to provide the original message. The value of this description key is known to the reviver.

Types of Cryptosystems 

Cryptosystems are classified into two different types. This categorization is based on the type of keys available in the system. The two types are: 

Symmetric Key Cryptosystems 

This system is known as private/secret key encryption or symmetric cryptography. Both the receiver and senders agree on the same secret key called the encryption key, as the name "Symmetric" suggests the same on both sides. 

In this system, firstly sender's message is encrypted using that secret key. Then the encoded message is decrypted using the same key at the receiver's side. The below illustration represents the flow of symmetric key encryption

Symmetric key

Various algorithms that provide symmetric-key encryption are:

  • DES - Data Encryption Standard
  • 3DES or TDES - Triple Data Encryption Standard
  • IDEA - International Data Encryption Algorithm
  • Blowfish

Asymmetric Key Cryptosystems

This system is also referred to as private key encryption. Encryption and decryption are performed using two different keys. A private and a public key are used in this system, which is mathematically related. The sender uses the public key of the receiver to encrypt the message. As it is very difficult to get information about the private key from the public key, it is shared freely. The digital certificate helps transmit public keys, which are very long and difficult to remember. The below illustration represents the flow of asymmetric key encryption.

Asymmetric key

Algorithms that provide asymmetric key encryption are:

  • RSA (Rivest, Shamir, Adleman)
  • DSA (Digital Signature Algorithm)
  • ECC (Elliptical Curve Cryptography)
  • Diffie Hellman Key Exchange

Challenges Faced

Symmetric Key Encryption 

Challenges faced by Symmetric key Encryption are:

  • Key Agreement - Before transferring information, the sender and receiver must agree on the same secret key. And for that, the system requires a secure key agreement mechanism.
  • Trust Issue - The sender and receiver share the same secret key. So, they must trust each other; otherwise, the message can be hacked. 
  • Key Updation - As this type of cryptosystem uses the public key. So, for secure communication, the key should be updated at regular intervals. 

Asymmetric Key Encryption

Challenges faced by Asymmetric key Encryption are:

  • Malicious Public Key - A third party should not spoof the public key. So, the user needs to check and trust the public key.
  • Manage the Key - The public keys are lengthy and difficult to remember. The third party manage these keys securely. The user can ask these third parties to provide the key when required.
  • Computation - The public and private keys are mathematically related to each other. The computation of the private keys is difficult, making the algorithm difficult. 

Cryptosystem Attacks 

Data security is the primary concern due to the increased number of cryptosystem attacks. Some of the standard types of attacks include:

  1. Brute Force Attack - The attack in which all combination of key or message is tried is known as a Brute force attack. This is very time-consuming, but the success rate is very high. The complexity can be increased by increasing the length of the key. 
  2. Implementation Attack - The attacks that profit from the cryptosystem's weakness is known as implementation attacks. All the errors and flaws in the cryptosystem are responsible for these attacks.
  3. Ciphertext Only Attack - This attack is the most brutal attack to carry out. In this, the attack has only a part of ciphertext to hack the message. Making the ciphertext complex and longer can make the attack almost impossible to crack. 
  4. Statistical Attack - The inability of true random numbers and statistical errors in the cryptosystem is the leading cause of these attacks. These attacks focus on the weaknesses in the operating system in which the system is working.
  5. Man in the Middle Attack - The attacker sits between two communicating parties. They start a session with the original user and another using a different key. The attacker has complete access to the traffic. 
  6. Known Plaintext Attack - In these attacks, the attacker has the original and the encrypted plaintext. The attacker tries to find the key used to encrypt. Once the attacker finds the key, they will get all the messages.

Our cryptosystem should be designed very securely to protect our data from these attacks. A Dutch cryptographer gave some rules for designing a good cryptosystem. Let's see what these rules are. 

Kerckhoff's Principle

According to Kerckhoff's principle, a cryptosystem should be designed securely, such that if, except the key, all other details are known, even then, it can not be hacked. 

kerckhoff principle

In the 19th century, a Dutch cryptographer, A. Kerckhoff, gave six rules defined by Kerckhoff's principle. These are - 

  • The cryptosystem should be practically unbreakable. 
  • We cannot keep the algorithms private. So, an attacker should get any information by knowing about the algorithm.
  • The key should be easily changeable and communicable. 
  • The encryption documents should be portable. 
  • The ciphertext should be transmissible. 
  • The system should be easy to use. 

Frequently Asked Questions

What are Cryptosystems?

Cryptosystems are computer systems that are also known as cryptographic or cipher systems. In cryptography, a cryptosystem is a set of algorithms used to encode and decode messages.

What is meant by symmetric key encryption?

The system in which the receiver and senders agree on the same secret key is symmetric encryption.

What does asymmetric key encryption mean?

The system in which the sender and receiver use two different keys for encryption and decryption is asymmetric key encryption. 

What is Kerckhoffs's principle?

According to this principle, a cryptosystem should design to be secure. So that the attacker should not get any information, even if everything except the key is known. 

Where can we use Cryptosystems?

Cryptosystems have many real-life applications like banking transactions, Electronic signatures, secure communication, etc.  


This article shows how cryptosystems can be used in secure communication. The article discusses the different types and attacks involved in cryptosystems. At last, we discussed the rules for creating a secure cryptosystem. 

We hope this article helps you on your journey. Don't stop just yet; there's much more about Cryptography for you to learn. You can find out more in the following articles-

You can also check out Difference between Public Key and Private Key

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