Cryptography
Cryptography helps protect information, detect changes, and verify who sent a message.
What you’ll learn
- Distinguish encoding, encryption, and hashing.
- Explain the role of a cryptographic key.
- Explore a historic cipher without mistaking it for modern security.
Three different jobs
Encoding changes how data is represented, such as Base64. It is not secrecy. Encryption transforms readable plaintext into ciphertext using a key; the right key lets you decrypt it. Hashing produces a fixed-length digest used to check data. It is designed to be one-way, not something you decrypt.
Keys make the difference
Symmetric encryption uses a shared secret key. Asymmetric cryptography uses a public key and a private key. For encryption, someone can use your public key to protect a message that your private key decrypts. Digital signatures use the private key to sign and the public key to verify. Keep private keys private.
Where you meet it
HTTPS uses TLS to protect data in transit between your browser and a server. It does not prove a website is honest. Device encryption helps protect stored files. Digital signatures help check authenticity and integrity. Security still depends on correct implementation and careful key handling.
Historic ciphers are learning tools
A Caesar cipher moves letters by a fixed number of positions. With a shift of 3, A becomes D. It is easy to break because there are only 25 nontrivial shifts. Modern applications need established cryptographic tools, not homemade ciphers.
Caesar cipher workbench
Type a practice message and change the shift. Then decode RZO VHFWRU using a shift of 3. Letters change; spaces and punctuation stay the same.
This historic cipher is a demonstration, not secure encryption.
Check your understanding
Choose one answer for each question, then check your answers. You can retry as often as you like.