What is a Cipher?
Definition, history, types and practical examples.
The word cipher is used to describe any method whose goal is to transform an original message (plaintext) into an unreadable message (ciphertext).
"Ciphers are the foundation of cryptography, a discipline that aims to protect information from ancient times all the way to the modern digital era."
1. Technical definition of a cipher
A cipher is an algorithm that takes a piece of text and modifies it according to a key, producing a version that appears meaningless. In cryptography, it is usually broken down into three core components:
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1
Plaintext The original, readable message.
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2
Key The secret value that controls the mathematical transformation.
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3
Ciphertext The encoded, unreadable result.
2. What is encryption used for?
🛡️ Privacy
Protecting private information from prying eyes.
💳 Finance
Securing credit cards and banking transactions.
🔐 Authentication
Verifying that you are who you say you are (passwords and logins).
🌐 Web browsing
The HTTPS padlock in your browser helps keep others from seeing what you visit.
3. A brief history of ciphers
Antiquity
1st century BC
Julius Caesar uses letter shifts to communicate with his generals.
Renaissance
15th–16th centuries
The polyalphabetic cipher appears with Vigenère, considered unbreakable for centuries.
20th century
World Wars
The Enigma machine mechanizes encryption. Alan Turing lays the groundwork for breaking these codes.
4. Types of ciphers
4.1. Classical ciphers (manual)
They use substitution or transposition rules applied to letters.
- Caesar cipher: Simple letter shift. Open tool →
- Vigenère cipher: Uses a keyword. Open tool →
- Playfair cipher: Encrypts pairs of letters using a grid.Open tool →
- Affine cipher: Uses a simple linear transformation. Open tool →
- Rail Fence cipher: Rearranges letters in a zigzag pattern. Open tool →
- Columnar transposition: Rearranges letters by writing them into a table and reading them by columns.Open tool →
4.2. Modern ciphers (digital)
They operate on bits and rely on advanced mathematics.
- AES (Advanced Encryption Standard): The de facto global standard for symmetric encryption.
- RSA: Based on factoring large prime numbers.
- ECC: Elliptic curve cryptography, offering strong security with shorter keys.
5. How does it work? The 3 pillars
Confusion
Hiding the relationship between the original message and the ciphertext.
Diffusion
Spreading the influence of each character throughout the whole message.
Key
The unique secret needed to reverse the process.
6. Conclusion
A cipher is a fundamental mechanism for protecting information. Understanding classical methods such as Caesar and Vigenère is a crucial first step towards grasping how the algorithms that protect our money and privacy work today.