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Technologies K–10 · Years 3–4

How long would guessing take: combination locks and passwords

Digital Technologies: Processes and production skills, Privacy and security (ACARA v9); no NSW code: neither the Science and Technology K–6 Syllabus (2017) nor the 2024 syllabus has a Stage 2 content point on passwords or guessing

Practical, model not builtLow risk

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The idea

Each extra dial or character multiplies the number of possible combinations, which is why a password should be easy for its owner to remember but take far too long for anyone else to guess.

What you need

  • 1 three-dial combination lock (digits 0 to 9) and 1 four-dial lock per group, with the combinations known only to the teacher
  • 1 stopwatch
  • Calculator
  • Recording sheet

How to do it

  1. Count the digits on one dial and the number of dials. Work out how many combinations the lock has.
  2. Time 20 honest tries on the three-dial lock (set the dials, pull the shackle) and work out the seconds per try.
  3. Work out the longest possible time to try every combination and the average time (half of the longest).
  4. Repeat the calculation for the four-dial lock.
  5. Compare with a 4-digit PIN and a 6-letter password made of lowercase letters.
  6. Write a rule for a school password that is easy to remember but hard to guess, using the Australian Cyber Security Centre advice on passphrases.

What you should see

A three-dial lock has 10 × 10 × 10 = 1,000 combinations and a four-dial lock 10,000. At the class's measured time per try, for example 2 s, trying every three-dial combination takes 2000 s (33 min 20 s) and 1000 s (16 min 40 s) on average, while the four-dial lock takes up to 5.56 hours. A 4-digit PIN has the same 10,000 possibilities as the four-dial lock; a 6-letter lowercase password has 308,915,776 possibilities. The Australian Cyber Security Centre recommends a passphrase of four or more random words. The learner knows it worked when they can explain why adding one dial multiplies the time by 10.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

  • A longer password is only a little harder to guess (each extra character multiplies the possibilities).
  • A password with my pet's name is safe because nobody knows it (people who know you, or your posts, can guess it).
  • Writing the password on the device is fine if it is small (anyone holding the device can read it).

Safety card

Low riskLearners carry it out

Hazards

  • Pinched fingers in the lock shackle

Controls

  • Pull the shackle gently

Note

No chemicals or heat.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

  • No NSW syllabus code is listed.
  • Australian Curriculum v9AC9TDI4P08

Sources

The pages the author read to write this activity.

  1. www.nsw.gov.au/education-and-training/nesa/curriculum/science/science-and-technology-k-6-2017
  2. curriculum.nsw.edu.au/learning-areas/science/science-and-technology-k-6-2024/outcomes
  3. www.cyber.gov.au/protect-yourself/securing-your-accounts/passphrases
  4. www.digitaltechnologieshub.edu.au/plan-and-prepare/scope-and-sequence-f-10/years-3-4
  5. curriculum.nsw.edu.au/learning-areas/science/science-and-technology-k-6-2024/content/stage-2/fa040571e3

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