OCR H446 1.3.1: Compression, Encryption and Hashing
The free BugBot lessons that teach this point, a robot to try it on, and the past-paper questions that test it.
What it covers
All three of these transform data with an algorithm. Compression makes data smaller, encryption makes it unreadable without a key, and hashing turns it into a short fixed-size value that cannot be turned back. At GCSE you met lossy and lossless compression, run length encoding and Huffman coding (F8.9), the Caesar cipher (F11.6) and hashed passwords (F11.5). A level adds dictionary coding, the one cipher that cannot be broken, the difference between perfect and computational security, and what hashing is used for.
- Lossy and lossless
- Run length encoding
- Dictionary coding
- Breaking the Caesar cipher
- The Vernam cipher
- Symmetric and asymmetric encryption
- Hashing
Or do it in the simulator, with tasks that mark themselves
Lessons that teach it
- A7.9 Compression, encryption and hashing Data representation
Run length and dictionary coding, the Caesar and Vernam ciphers, symmetric and asymmetric encryption, and hashing. - A7.10 Project: a secure sensor packet Data representation
Pack a distance reading into fixed point bytes with flags and a checksum, encrypt it with a one-time pad and send it by radio.
Try it on a robot
The task from A7.9 Compression, encryption and hashing, running here. Change the program and press Run.
The specification is OCR's own document; this page says which of our lessons teach point 1.3.1 and is not endorsed by the board.