Public Key Encryption

Kid Krypto #

Public key encryption is an extraordinary recent development that has made internet commerce possible. It allows people to encrypt and decrpyt messages without having to share a password to unlock them. It is hard to believe that such a system could exist, yet this mode of encryption is widely used because it is so easy to set up.

This activity works with two people, but it’s most exciting with a whole class, with everybody else trying to intercept a message sent between two students.

This activity is fairly demanding, and requires students to be careful in the way the encode messages. Also, the samples provided here are aimed at junior high students; some younger students may find it too difficult, and more capable or older students are likely to need more complex “maps” to make the encryption convincing, since the one provided can be solved relatively easily. Balancing the amount of tedious effort required for large maps against the insecurity of smaller maps needs to be done by the teacher, although this issue can be a discussion point for the class, since the goal is to understand the issues around encryption.

Activity description (PDF) #

• Instructions for Public Key Encryption activity (English)

Translations and other versions #

• Chinese language version
• Polish language version
• Slovenian language version

Video #

See our video page.

Related Resources #

More lessons and activities #

• Misha Leder, a Software Engineer at Google has an activity called Privacy and Encryption which can be a nice extension activity on sending  a secret message to your friend via Internet.
• The Royal Institution UK and Microsoft Research together have produced activities in encryption, cryptography, and zero knowledge protocols for the classroom at the locations below:
  • Keeping secrets secret
  • Zero-knowledge games
• Frank Tapson – Centre for Innovation in Mathematics Teaching has an informative booklet on Public Key Cryptography developed as a resource for Modulo Arithmetic Maths Curriculum.
• Centre for Innovation in Mathematics Teaching has the following teaching package in Modern Encryption developed to teach Codes and Ciphers in their Maths Curriculum: Modern Encryption: Teacher Guide, Student Guide, OHP Slides, Lesson Plans.
• Try Engineering has an activity called Hand Biometrics Technology which explores how engineers incorporate biometrics technologies into products, but also explores the challenges of engineers who must weigh privacy, security and other issues when designing a system. Students explore different biometrics techniques, find their own hand geometry biometrics, then work in teams of “engineers” to design a high-tech security system for a museum. Download Full Lesson Plan and Student Worsksheets.
• CS4FN has the following online activities/articles that demonstrates concepts in Binary and Gray code :
  • Locking a Dead Man’s Chest
  • The French Peasant’s Lock and Gray Code
• nrich Maths has the following activities with notes and solutions provided:
  • The Public Key
  • Public Key Cryptography
  • The Knapsack Problem and Public Key Cryptography. See also Knapsack

If you want to find out more #

• Wikipedia: Public Key

Videos #

• Hashing Algorithms and Security – Computerphile
• Encryption and Security Agencies – Computerphile
• EXTRA BITS – Data Security and Flash Memory – Computerphile
• Security of Data on Disk – Computerphile
• Public Key Cryptography – Computerphile

Curriculum Links #

Great Principles of Computer Science #

• Communication