The First Steps: Classical Ciphers That Shaped Cryptography

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Caesar Cipher: The Simplicity of Substitution

One of the earliest known ciphers, the Caesar cipher, was used by Julius Caesar to protect military communications. It involved shifting letters in the alphabet by a fixed number. For example, shifting by 3 places:

🔒 Plaintext: HELLO
🔑 Shift: +3
🔓 Ciphertext: KHOOR

While it provided basic security in ancient times, the Caesar cipher is incredibly weak by modern standards. A simple brute-force attack (trying all 25 possible shifts) can easily break it.

Vigenère Cipher: The First Step Towards Complexity

To counteract the weaknesses of simple substitution ciphers, the Vigenère cipher introduced a keyword-based shifting pattern, making it polyalphabetic (meaning it used multiple alphabets). This made frequency analysis more difficult—at least for a while.

Example using LEMON as a keyword:

🔒 Plaintext: ATTACK
🔑 Key: LEMONL
🔓 Ciphertext: LXFOPV

For centuries, the Vigenère cipher was thought to be unbreakable. However, in the 19th century, Friedrich Kasiski developed a method to analyze repeated patterns, making it vulnerable to cryptanalysis.


Playfair Cipher: A Shift to Digraphs

Invented by Charles Wheatstone but promoted by Lord Playfair, the Playfair cipher encrypted pairs of letters (digraphs) instead of single letters. This made frequency analysis much harder, but it wasn’t foolproof. Given enough ciphertext, analysts could still detect patterns.


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