Intro to Computer Science / Unit 10: Cybersecurity and Impacts of Computing
10.2 Encryption Basics
Notes
Encryption scrambles data (plaintext) into unreadable form (ciphertext) using a key. Decryption turns it back.
- Caesar cipher: shift each letter a fixed number of places. With shift 3, A becomes D, B becomes E, and so on.
- Example: HELLO with shift 3 becomes KHOOR.
- Symmetric encryption uses the same key to encrypt and decrypt. Public-key (asymmetric) encryption uses a public key to encrypt and a private key to decrypt.
- HTTPS uses encryption so that data on the network cannot be read by others.
- Simple ciphers like Caesar are easy to break (only 25 shifts), so real systems use complex math and long keys.
Practice
What is the Caesar cipher (shift 3) of the word CAT?
C to F, A to D, T to W.
In public-key encryption, which key do you keep secret?
The private key is kept secret and used to decrypt messages.
Why is the Caesar cipher not secure today?
With 25 possible shifts, a computer can try them all instantly.
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