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Network Security: Classical Encryption Techniques

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Cryptography is securing communication and data by converting it into an unintelligible form, known as ciphertext, using mathematical algorithms and techniques. It is an essential component of information security and ensures data confidentiality, integrity, and authenticity.

This article explores the fascinating world of classical encryption techniques. From the ancient Caesar cipher to the intricate Enigma machine, discover how these early methods shaped the foundations of cryptography.

Table of Contents

What is Cryptography?

Cryptography is the practice and study of techniques used for secure communication in the presence of third parties, often referred to as adversaries. It involves the art and science of encoding and decoding information to protect its confidentiality, integrity, and authenticity.

Source: AU

The primary goal of cryptography is to ensure that sensitive information remains secure during transmission or storage. It provides mechanisms to transform plaintext (unencrypted data) into ciphertext (encrypted data) using cryptographic algorithms and keys. The encrypted data can only be decrypted back to its original form by authorized individuals possessing the appropriate decryption key.

Cryptography employs various cryptographic algorithms and protocols to achieve different security objectives. These algorithms can be symmetric (where the same key is used for encryption and decryption) or asymmetric (where different keys are used for encryption and decryption). Symmetric encryption algorithms include DES, AES, and 3DES, while asymmetric encryption algorithms include RSA, DSA, and ECC.

In simple words…

Cryptography is the procedure of converting the original text (unencrypted data) into unreadable text (encrypted data) through Cryptography algorithms. It makes the original text difficult to understand and can’t be understood until the text is converted back to the original text.

Source: AU

Definitions of Terms in Cryptography

Certainly! Here are definitions for some standard terms used in cryptography:

  1. Plaintext: The original, unencrypted data or message in a readable format.

  2. Ciphertext: The encrypted form of the plaintext, obtained by applying cryptographic algorithms and keys. It appears as unintelligible or scrambled data.

  3. Encryption: Converting plaintext into ciphertext using cryptographic algorithms and keys. It ensures confidentiality by making the data unreadable to unauthorized individuals.

  4. Decryption: Converting ciphertext back into plaintext using the appropriate cryptographic algorithms and keys. It allows authorized recipients to retrieve and understand the original data.

  5. Cryptographic Algorithm: A mathematical function or set of rules used to perform encryption, decryption, digital signatures, or other cryptographic operations. Examples include AES, RSA, and ECC.

  6. Key: A piece of information used by cryptographic algorithms to control encryption and decryption. Keys can be symmetric or asymmetric.

  7. Symmetric Key Cryptography: A cryptographic method using the same key for both encryption and decryption. The sender and receiver share this secret key. Examples include AES and DES.

  8. Asymmetric Key Cryptography (Public-Key Cryptography): A cryptographic method that uses a pair of mathematically related keys: public and private keys. The public key is freely distributed, while the private key is kept secret. RSA and ECC are examples of asymmetric key algorithms.

  9. Key Distribution: The secure sharing or exchange of cryptographic keys between parties involved in secure communication or data transfer.

  10. Digital Signature: A cryptographic technique used to verify the authenticity and integrity of digital messages or documents. It involves using the sender’s private key to create a unique digital signature that can be verified using the corresponding public key.

  11. Hash Function: A mathematical algorithm that takes an input (message or data) and produces a fixed-size output called a hash value or hash code. Hash functions are used for data integrity checks and password storage.

  12. Certificate: A digital document that binds an entity’s identity (such as a website or individual) to its public key. Certificates are issued by trusted Certificate Authorities (CAs) for authentication and secure communication.

  13. Key Exchange: Securely sharing or establishing a shared secret key between parties involved in secure communication. Diffie-Hellman is a commonly used key exchange algorithm.

  14. Steganography: The practice of hiding secret information within seemingly innocuous carrier data (such as images or audio files) to conceal its existence. It aims to provide covert communication rather than secure encryption.

Goals of Cryptography

  1. Confidentiality: Cryptography ensures that only authorized parties can access and understand the information. Encrypting data becomes unreadable to anyone who still needs to possess the corresponding decryption key.

  2. Integrity: Cryptographic techniques allow for the verification of data integrity. It ensures that data remains intact and unaltered during transmission or storage. Any modification to the data can be detected through cryptographic mechanisms.

  3. Authentication: Cryptography provides methods for verifying the identity of individuals or systems involved in a communication or transaction. It ensures that the parties involved are who they claim to be and that the data hasn’t been tampered with.

  4. Non-Repudiation: Cryptographic techniques can prevent individuals from denying their involvement in a communication or transaction. Through digital signatures or other cryptographic mechanisms, it becomes possible to prove the origin and integrity of data, thus ensuring non-repudiation.

Cryptography relies on cryptographic algorithms, which are mathematical functions designed to transform plaintext (the original data) into ciphertext (the encrypted data) and vice versa.

Cryptography used in applications

  1. Secure Communication: It ensures the confidentiality and integrity of sensitive data during transmission over insecure networks, such as the internet. Examples include secure messaging protocols like SSL/TLS for secure web communication and PGP for email encryption.

  2. Data Protection: Cryptography safeguards data at rest, such as encrypted file systems, disk encryption, and database encryption. It prevents unauthorized access to data even if physical storage media are compromised.

  3. User Authentication: Cryptographic techniques are employed for secure authentication and identity verification, such as password hashing, digital signatures, and digital certificates.

  4. Digital Rights Management (DRM): It enables content creators and distributors to protect digital content from unauthorized copying or distribution by encrypting and controlling access to the content.

  5. Cryptocurrency: Cryptography is fundamental to the security and operation of digital currencies like Bitcoin and Ethereum. It ensures the integrity of transactions, protects wallets and private keys, and enables secure peer-to-peer transactions.

Types of Cryptographic Algorithms

Source: AU
  1. Symmetric-key cryptography: In symmetric-key cryptography, the same key is used for encryption and decryption. The sender and receiver must share this secret key in advance. Symmetric-key algorithms are generally faster but require a secure method for key distribution.


  2. Asymmetric-key Cryptography (also known as public-key cryptography): Asymmetric-key cryptography uses a pair of mathematically related keys, public and private keys. The public key is freely distributed, while the private key is kept secret. Messages encrypted with the public key can only be decrypted using the corresponding private key. Asymmetric-key algorithms provide secure key exchange and digital signatures.
Source: AU

Common Cryptographic algorithms include Advanced Encryption Standard (AES), RSA, Diffie-Hellman, and Elliptic Curve Cryptography (ECC). These algorithms provide the mathematical foundation for encryption, decryption, digital signatures, and other cryptographic operations.

Cryptography is widely used in various applications, such as secure communication (e.g., HTTPS for fast web browsing), secure storage (e.g., encrypted hard drives), secured transactions (e.g., online banking), and authentication mechanisms (e.g., password hashing). It is crucial to protect sensitive information in today’s digital world.

Model of Symmetric Cryptosystem

The model of a symmetric cryptosystem, also known as symmetric-key cryptography, involves using the same key for both data encryption and decryption. 

Source: AU

Here is a simplified model of a symmetric cryptosystem:

  1. Plaintext: The original, unencrypted data or message intended to be protected.

  2. Encryption Algorithm: A mathematical algorithm that inputs the plaintext and secret symmetric key to produce ciphertext. The encryption algorithm transforms the plaintext into an unreadable and scrambled form.

  3. Secret Symmetric Key: A shared secret key between the sender and the intended recipient. Both parties must have access to the same key before communication begins.
Source: AU

4. Ciphertext: The encrypted form of the plaintext obtained by applying the encryption algorithm using the secret symmetric key. The ciphertext appears as unintelligible and scrambled data.

5. Decryption Algorithm: A mathematical algorithm that takes the ciphertext and the secret symmetric key as inputs to reverse the encryption process and recover the original plaintext. The decryption algorithm transforms the ciphertext back into readable plaintext.

6. Decryption Key: The same secret symmetric key used for encryption. The recipient uses it to decrypt the ciphertext and obtain the original plaintext.

The symmetric cryptosystem model assumes that the sender and recipient securely share the secret symmetric key through a trusted channel before communication occurs. The strength of the security relies on the secrecy and integrity of the key. If an unauthorized party gains access to the key, it can decrypt the ciphertext and obtain the plaintext.

Common symmetric encryption algorithms include Advanced Encryption Standard (AES), Data Encryption Standard (DES), and Triple DES (3DES). These algorithms provide secure and efficient encryption and decryption operations, making them suitable for various applications, such as secure communication, data storage, and confidentiality protection.

It’s worth noting that key management and distribution are critical considerations in symmetric-key cryptography. Securely exchanging and storing the secret symmetric key is essential to maintain the confidentiality of the encrypted data.

Source: AU

What is Brute – Force Attack?

A brute-force attack is a method attackers use to crack passwords or encryption keys by systematically trying all possible combinations until the correct one is found. It is a straightforward yet time-consuming approach that assumes that the attacker can eventually discover the valid password or key through sheer computational power.

In password cracking, a brute-force attack involves trying every possible combination of characters until the correct password is found. This typically involves attempting all possible character combinations, starting from the shortest passwords and gradually increasing the length. For example, the attacker would try all possible combinations if a password consists of lowercase letters and numbers and is six characters long.

Similarly, in the context of encryption keys, a brute-force attack involves trying all possible encryption keys until the correct one is found. The attacker systematically generates and tests each possible key until the encryption is decrypted.

To reduce the risk of brute-force attacks, several measures can be implemented, including:

  1. Strong Passwords: Encourage users to create strong, complex passwords that are difficult to guess.

  2. Password Policies: Implement password policies that enforce password complexity requirements, regular password changes, and account lockouts after multiple failed login attempts.

  3. Account Lockouts: Implement mechanisms that lock user accounts temporarily or permanently after multiple failed login attempts to prevent automated brute-force attacks.

  4. Rate Limiting: Apply rate limiting or throttling techniques to restrict the number of login attempts allowed within a specific timeframe, making it harder for attackers to guess passwords.

  5. Two-Factor Authentication (2FA): Implement additional layers of authentication, such as 2FA, to require users to provide a second form of verification, making it more challenging for attackers to gain unauthorized access.

  6. Strong Encryption: Utilize robust encryption algorithms and sufficiently long encryption keys to make brute-forcing the encryption impractical within a reasonable timeframe.

By implementing these security measures, organizations and individuals can significantly reduce the vulnerability to brute-force attacks and enhance the overall security of their systems and data.

Rotor Cipher Machine

The Rotor Cipher Machine, also known as the Enigma machine, is a famous example of a rotor-based encryption device widely used during World War II for secure communication. German engineer Arthur Scherbius initially developed it in the 1920s and later modified and improved by the German military.

Source: AU

The Enigma machine is an electromechanical device consisting of several rotating disks, or rotors, each with a series of electrical contacts and corresponding wiring. The machine also includes a plugboard and a reflector. Here’s a simplified overview of how the rotor cipher machine works:

  1. Electrical Connections: Each rotor has a set of electrical contacts on both sides, with wires inside connecting pairs of contacts. The positions of the wires determine the mapping between input and output letters. The rotor wiring is configurable and changed regularly to increase security.


  2. Keyboard Input: The user enters a plaintext letter by pressing a key on the keyboard.


  3. Plugboard: The input letter first passes through the plugboard, where selected pairs of letters are swapped. This adds a layer of encryption before the signal enters the rotors.


  4. Rotors: The signal then goes through a series of rotors. Each rotor has a different wiring configuration, which causes the electrical signal to be scrambled. The rotors rotate as the user types subsequent letters, changing the electrical connections and creating a complex substitution cipher.


  5. Reflector: After passing through the rotors, the electrical signal hits a reflector, which further scrambles the signal by reflecting it through the rotors but along a different path.


  6. Output: The reflected signal finally emerges from the rotors and plugboard, and the corresponding ciphertext letter is displayed on a lamp panel or printed on paper.


  7. Recipient Setup: To decrypt the message, the recipient sets their Enigma machine to match the sender’s machine settings, including the rotor positions and plugboard connections. They enter the received ciphertext, and the machine performs reverse encryption to reveal the plaintext.

The Enigma machine’s strength relied on many possible rotor configurations, making it difficult for adversaries to decipher intercepted messages. However, due to weaknesses in how the machine was operated and some mathematical breakthroughs, cryptanalysts at Bletchley Park eventually cracked the Enigma cipher, including the famous codebreaker Alan Turing.

Source: AU

The Enigma machine played a significant role in the history of cryptography and computing and has become an iconic symbol of early encryption devices. It serves as a reminder of the ongoing arms race between encryption and decryption techniques in information security.


Classical encryption techniques played a significant role in the evolution of cryptography. Still, their vulnerabilities and limitations highlight the need for more advanced and secure encryption methods to meet the challenges of today’s digital world.

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