Craig 'n' Dave

OCR A level (H446) SLR 09 – Compression, Encryption & Hashing

This download provides you with a zip file which contains all the resources you will need to deliver this topic.

It includes:

  • Student Learning Record (A3 version in word)
  • Student Learning Record (PDF version)
  • Student Learning Record (PowerPoint version)
  • Set of student activities and workshops with answers
  • Answers to the exam questions from the back of the SLR
  • Teacher Marking Checklist

This topic covers:


  • 1.3.1 a-d Compression, Encryption and Hashing

Specific knowledge required for A Level:

  • Candidates need to understand the need for compression, especially when transferring data via the
  • Candidates need to understand the difference between lossy and lossless compression, and the benefits and drawbacks of each type.
  • Candidates need to be able to recommend a type of compression for a given scenario.
  • Candidates need to understand how run-length encoding can reduce the size of a file for example with a text file or image.
  • Candidates should understand how dictionary coding works by substituting entries with a unique code.
  • Candidates should have practical experience of using these algorithms with small example files.
  • Candidates should understand the need for encryption. Candidates should understand how symmetric and asymmetric encryption work to encrypt and decrypt data.
  • Candidates should understand the need for and purpose of using hashing algorithms to store data.
  • Candidates should be aware of different uses for hashing, such as the storing of passwords.

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