Cryptography keeps a message secret. Encryption changes readable plaintext into scrambled ciphertext; decryption reverses it back to plaintext.
Plaintext, ciphertext and key
The original message is the plaintext. After encryption it becomes ciphertext, which looks like nonsense to anyone without the key. Only someone with the correct key can decrypt and read it. This lets a message travel over the internet safely: even if someone intercepts the ciphertext, they cannot understand it without the key. Cryptography is used every day to protect passwords, online banking and private chats.
Key idea
Encryption: plaintext + key → ciphertext. Decryption: ciphertext + key → plaintext. The key controls how much the message is scrambled.
The Caesar cipher
The Caesar cipher is a simple substitution cipher. It shifts every letter a fixed number of places along the alphabet. With a shift of 3, A becomes D, B becomes E, and so on. Letters near the end wrap around, so with a shift of 3, Y becomes B and Z becomes C.
Example
Encrypt the plaintext CAT with a Caesar shift of 3. C→F, A→D, T→W, so the ciphertext is FDW. To decrypt, shift each letter 3 places back: F→C, D→A, W→T, giving CAT again.
Remember
- Encryption hides the message; decryption reveals it.
- The Caesar cipher shifts letters by a fixed amount.
- Letters wrap from Z back to A when shifting.
- A larger shift does not make Caesar much safer; it is easy to break.