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Cryptography is the science of making messages secure. It prevents unwanted people from reading the messages and allows only the intended people to recover the original message.
Let’s imagine a situation where Alice wants to send a secret message to her friend Bob, but she doesn’t want anyone else to know, especially her little sister Eve or her parents. She wants to ask Bob out for a secret date, but she is afraid that her parents will find out and forbid her. How sad.
She needs a way to make her message unreadable to anyone except Bob. This aspect of cryptography is called message confidentiality.
Luckily, Alice has a friend who knows a lot about cryptography. His name is CryptoDev and he is the master of secret messages. Alice asks CryptoDev for help and he agrees to teach her some cryptography.
Alice: What is cryptography?
CryptoDev: Cryptography is the art of making messages secure by using secret keys and algorithms.
Alice: What is a secret key?
CryptoDev: A secret key is a number that you use to transform your message into something that looks like nonsense. This process is called encryption.
Alice: What is an algorithm?
CryptoDev: An algorithm is a set of rules that you follow to encrypt or decrypt your message.
Alice: What is decryption?
CryptoDev: Decryption is the opposite of encryption. It is the process of using the secret key to recover the original message from the nonsense.
Alice: How can I share the secret key with Bob without anyone else knowing?
CryptoDev: That’s a good question. You can use a special algorithm called Diffie-Hellman key exchange. It was invented by my friends Whitfield Diffie and Martin Hellman. They were very clever and found a way to exchange secret keys without revealing them.
CryptoDev then explains to Alice how the Diffie-Hellman key exchange works and gives her the algorithm as a gift. He also gives Bob the same algorithm and tells him to wait for Alice’s message.
Alice then asks her little sister Eve to deliver some messages to Bob in exchange for some candy. Eve agrees, but she doesn’t know what the messages mean. They are just numbers that Alice and Bob use to exchange their secret keys. After they have their secret keys, Alice encrypts her message with her key and sends it to Bob. Bob decrypts it with his key and reads it. He is happy and replies with another encrypted message.
Alice and Bob manage to arrange their secret date without anyone knowing. They have a wonderful time.
Happy ending!!! Right?
This is just the beginning of our journey into cryptography. There are many more adventures waiting for us.
Stay tuned.