Holy Riddle - the secret language of shadows

Did you know that humans have wanted to hide their messages since the dawn of time? From the first cave paintings, communicating without being understood by everyone has been an obsession—there are truths that cannot travel in broad daylight. There are secrets that should only be read by those who hold the key.

Welcome to the world of cryptography.

What is cryptography?

Cryptography is the art of hiding a message in plain sight. It is the science of turning readable information (plaintext) into something incomprehensible (ciphertext) and vice versa. It is not new; it has centuries of history.

A journey through time: the first ciphers

• Egypt and Mesopotamia already hid meanings in their symbols.
• The Greeks and Romans invented methods like the Caesar cipher, where each letter was shifted a fixed number of positions.
• In the Middle Ages, methods like the Vigenère cipher emerged, using keywords to further mix messages.

Every culture, every era, every war... brought a new way to protect information.

Cipher, steganography, or encoding?

It's important not to confuse:

• Encoding: transforming data so systems can understand it (e.g., Base64, ASCII). It does not aim to hide.
• Steganography: hiding a message within another (like an image with hidden text in its pixels).
• Cryptography: hiding the real meaning, making the message unreadable without a key or method.

Cryptography is not a game; it is a tool of power.

Modern cryptography

Today we protect our data with algorithms like:

• AES (Advanced Encryption Standard) – used to encrypt files, messages, and connections.
• RSA – a public-key system based on complex mathematics (prime factors).
• Elliptic Curve Cryptography (ECC) – uses mathematical curves to provide security with fewer resources.
• SHA-2, SHA-3 – hash functions to verify data integrity.

And beyond...

Quantum and post-quantum cryptography

In the quantum era, classical computers will not be enough to protect us. That's why post-quantum cryptography was born, seeking algorithms that even quantum computers cannot break.

• QKD (Quantum Key Distribution): allows sharing keys so that no one can eavesdrop without being detected.
• Lattice-based cryptography: a hope to withstand quantum power.

The future is near, but it all began with simple methods that inverted the world with just a reflection.

How is a secret key shared?

The Diffie-Hellman algorithm

Imagine Alice and Bob want to share a secret key without Eve (the spy) seeing it.

• Both agree on a base number g and a prime number p. This is public.
• Alice chooses a secret number a, calculates A = g^a mod p and sends it to Bob.
• Bob does the same with his secret number b, calculates B = g^b mod p and sends it to Alice.
• Then:
  • Alice calculates K = B^a mod p
  • Bob calculates K = A^b mod p

Both obtain the same secret key without having sent it directly. Eve, even if she sees A, B, g, and p, cannot know the real key without knowing the secrets a and b.

It's like exchanging locked boxes and invisible keys.

Real-world uses of cryptography

• Protecting your messages on WhatsApp
• Preventing fraud in bank cards
• Securing classified files in governments
• Signing digital contracts
• Authenticating users in complex systems

Even now, as you read this... there are dozens of processes encrypting and decrypting around you.

✨ One last clue...

Sometimes you don't need a powerful machine to decipher something. You just need to look at it backwards, or as if it were in a mirror.

Remember: the oldest methods are sometimes the most effective, and some secrets are only revealed when you read them from the right perspective.

See you in the shadow of the letters,