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OCR H446 1.3.1 Compression, encryption and hashing consolidation
Part 6 of 7 · H446 1.3.1 · Compression, encryption and hashing
Compression, encryption and hashing meet in one running project scenario here, which is the consolidation point for H446 1.3.1 rather than three separate topics revisited. No new content is introduced, so it works as a revision lesson or a checkpoint before the assessment.
Students will:
- recommend lossy or lossless compression for contrasting files within the same project
- encode one sequence under both field orders and explain what a decoder must be told
- build and decode a first-appearance dictionary, then account for its cost
- trace an asymmetric confidentiality journey and say when a symmetric method becomes practical
- trace password verification and a release-file digest check, stating what each match can support
Inside: 5 explanation cells, 1 multiple-choice question, 1 fill-in-the-blanks cell and 5 written answers. 49 marks, about 45 to 60 minutes.
Series: H446 1.3.1 · Compression, encryption and hashing, part 6 of 7.
Shared by Coding PathwayVerified teacher
- 12 cells
- About 45 minutes
- CC BY-SA 4.0
- Shared 31 Aug 2026
- Updated 3 Sept 2026
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Compression, encryption and hashing consolidation
Complete the sections in order, beginning with closed-book retrieval and then applying the ideas in the integrated contexts. No new required knowledge is introduced.
Episode A: a remote ecology project
A team uploads low-detail preview audio, exact sensor tables and compact status sequences. Its first status sequence is SSSSTTTUUSS. Another file contains the tokens NEST RIVER NEST FIELD RIVER NEST.
Recommend lossy or lossless compression for the preview audio and exact sensor tables. Compare both methods in each context and connect the upload constraint to a consequence.
Use acceptable quality/size for the preview and exact reconstruction/meaning for the table.
Students type their answer here.
For SSSSTTTUUSS, (a) encode using symbol-count, (b) encode using count-symbol, and (c) explain which field order a decoder must know. Then show why symbol-count RLE expands STSTST when symbols and counts use equal-width fields.
Segment runs first and label each convention.
Students type their answer here.
Construct a first-appearance dictionary and coded stream for NEST RIVER NEST FIELD RIVER NEST, then decode it. Explain why the dictionary cost must be included before claiming a saving.
Show dictionary, stream and reconstructed sequence.
Students type their answer here.
Apply the ideas together
The next section combines earlier ideas in a changed context. Complete it independently, returning to a worked model only when you have identified a specific misconception to repair.
Episode B: protect accounts and reports
Public volunteers must send confidential reports to project lead Imani without a pre-shared secret. The service also verifies volunteer passwords and checks whether downloaded map files match a recorded release digest.
Trace the asymmetric confidentiality journey for a volunteer sending a report to Imani. Then state when a symmetric method could become practical for a protected local archive. Include one limitation of each route.
Name owner, public/private/secret key, plaintext and ciphertext. Do not use a sender-private confidentiality shortcut.
Students type their answer here.
Trace password verification and map-file digest comparison. For each, state what is hashed, what is compared, and what a match can support. Explain why neither process decrypts a digest or guarantees confidentiality.
Use two ordered comparison processes, then distinguish their claims.
Students type their answer here.
Which statement describes a hash table rather than secure password hashing?
- AA candidate password is hashed and compared with a stored digest
- BA file digest is recomputed to check for change
- CA one-way verification value is stored instead of plaintext
- DA key is mapped to an index or bucket used to locate a stored record
Review your responses
Use the evidence in your completed responses to identify the first model, state transition or reasoning link that needs improvement. Correct that point, then reapply it to the changed context.