[Level 2] Computer Science Concepts: Compression, Error Control, Encryption

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What is this Resource?

This document was prepared by Sumant Murugesh and Tim Bell at the University of Canterbury. It is not an official document, but is offered as an evolving guide to the resources that are available for teaching the new material in NCEA Digital Technologies (currently focussed on the Programming and Computer Science strand). The structure has been based on various versions of the Body of Knowledge, proposed Standards, and Teaching and Learning guide; the material comes from an extensive search for relevant resources. It is our hope that this resource will evolve based on feedback from teachers, and ultimately end up as teaching plans that are built on the resources. Feedback can be sent to tim.bell [at] canterbury.ac.nz.

Achievement Standard
The resources on this page relate mostly to the proposed Digital Technologies Achievement Standard 2.44/AS91371 (Demonstrate understanding of advanced concepts from computer science)

Objectives
Demonstrate an understanding of the fundamental concepts of encoding information using data compression, error detection and correction and encryption from computer science

  • Understand how coding for compression enables technologies such as MP3 players
  • Become aware of error detection and correction used in data communication and how error detection techniques allow detecting errors, while error correction enables reconstruction of the original data.
  • Understand the concept of encryption in cryptography as the process of transforming information using an algorithm (called cipher) to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key.
  • Evaluate a widely used system for compression coding, error control coding, or encryption

Context
The aim here is to create an awareness of the coding for compression that goes into modern day devices such as the MP3 players and other hand held devices. Also familiarise students with the concept of errors that can occur in data transmission or storage, and correction techniques that are available such as checksums in barcodes. The importance of data security and encryption used in e-commerce such as on websites, and understand the basic terminology and issues of cryptography through some activities and games.

Ideas for Teaching and Learning Activities

Our Picks
Here is a list of resources we have picked from the comprehensive list below that were either developed for high school use or can be easily adapted for the purpose.

  • SECRET CODE BREAKER provide detailed instructions explaining how to "crack" secret codes and ciphers for young readers


Comprehensive list of resources that relate to this standard

The resources below are a mixture that were developed for a varied audience ranging from high school students to university undergraduates, therefore we have attempted to classify the resources in terms of their readiness to be used by teachers. There are those that aim to convey a Basic understanding of the concepts and those that are Advanced and therefore might assist teachers with their professional development activities.


Online Guides: Basic Resources

  • CryptoDox is a free encyclopedia on cryptography and information security. Teachers can use this site for reference just like Wikipedia; students could use this site for research purposes
  • DIMACS, Rutgers University has the following sections for teaching Cryptography & Network Security at high school level:
    1. Keeping Secrets: a great section discussing some topics which could be addressed in some high school courses
    2. Teacher breaks code on summer vacation: article about Connie Cunningham, a math teacher at Rocky Grove High School, learned the mathematics behind cryptography at a summer forum at Rutgers State University.
  • Teachers Resources Online (hosted at Cleve Books UK) has a complete set of resources for teaching Cryptology developed by Frank Tapson to introduce the different Ciphers and Codes:
    1. Notes on Cryptology and Lesson Index
    2. Scrambled Messages: How an ordinary message can re-arranged, in an orderly manner, so as to make it very difficult to read.
    3. Buried Messages: Disguising a message so that it does not even look as though it contains any secrets.
    4. Coded Messages: Using a code allows messages to be hidden and shortened at the same time.
    5. Simple Cipher Messages: Hiding the messages by substituting other letters for those of the original text
    6. Addition Ciphers: Using numbers and some simple arithmetic to hide a message
    7. Multiplication Ciphers: How more complex arithmetic processes bury the messages even deeper.
    8. Rotor Ciphers: Mechanical enciphering with a (very!) simplified paper model of the Enigma machine.
    9. Cryptanalysis: The science (or is it an art?) of breaking cipher messages, allowing them to be read without knowing the keyword or its equivalent.
    10. Other Systems: Accounts of some other methods for creating ciphers.
    11. Public Key Ciphers: How one particular modern cipher system (RSA) works, and can be made widely available to all, whilst retaining its security.
    12. Additional Materials: While all sections contain their own support materials, this has a few more general items.
    13. The Small Code Book: An abbreviated code book which can be printed out and assembled.For use with Coded Messages (above).
    14. Display Material: Diagrams suitable for making ohp slides or even projected directly onto a suitable screen or whiteboard.
    15. The Gold Bug: The famous short story by Edgar Allen Poe about cipher breaking which was the first account to appear in a work of fiction.
    16. The Dancing Men: The story of how Sherlock Holmes broke a symbol cipher.
  • National Cyber Security Alliance in association with StaySafeOnline has the Resource Library with excellent resources prepared for schools in the USA. The NCSA produces a wide range of documents and resources, including tip sheets, materials to support National Cyber Security Awareness Month, and research reports. To make them easier to download and share, we have created the NCSA Resource Library. Some resources are available as Word documents, some as PDFs, and some as both. Feel free to use them in your education and awareness efforts. For more information about using NCSA materials, check out our About Us section.
  • C-SAVE (Cyber Security Awareness Volunteer Education Program) have developed classroom materials and other resources to support volunteers. There is no need to sign up or register (although you can opt in to receive email updates). These resources are available to all school levels including high school.
  • Fabien Petitcolas has the following pages that use Steganography:
    1. the image downgrading problem: illustration of information covertly hidden in a ‘top secret’ image for later retrieval when the image is declassified.
    2. mp3stego: MP3Stego will hide information in MP3 files during the compression process. The data is first compressed, encrypted and then hidden in the MP3 bit stream.
  • SECRET CODE BREAKER is a comprehensive site covering a series of cryptography publications for young readers that provide detailed instructions explaining how to "crack" secret codes and ciphers for beginning cryptanalysts. Included are computer programs for code breaking and a series of coded secret messages actually sent by secret agents, spies and military commanders beginning with the Revolutionary War to the present including messages from the CIA "mole" Aldrich Ames to the KGB.

  • Oliver Johnson (hosted at +plus magazine) has an article Text, Bytes and Videotape: How can a 3 hour long film like the Lord of the Rings fit on a single DVD? Hw cn U rd txt msgs? How do MP3s make music files smaller, so they can be downloaded faster off the Internet? All these things rely on the mathematics of data compression.
  • Top Spy Secrets have the following articles of interest:
    1. Introduction to Codes and Ciphers
    2. The Ceasar Cipher - This cipher (aka. shift cipher) is a substitution cipher, where letters are replaced by a letter with a fixed shift in the alphabet
    3. Pigpen Cipher - The pigpen cipher (aka. masonic cipher) is a very simple substitution cipher, that goes back all the way to the 18th century
    4. Vigenere Cipher - The Vigenère cipher (which is actually French and sounds a bit like visionair) is a very old way of coding that's designed to mask character frequency (checking character frequency in a piece of coded text is one of the most well-known ways of breaking code)
    5. View the entire site for more activities and ideas
  • John W. M. Russell's Cryptology Home Page is a complete site dedicated to fundamentals of cryptology - the science of secure communication. It will not delve too deeply into mathematical proofs but is more for those who wish to be aware of some of the basic history, techniques and strategies of code making and code breaking.

 

Online Guides: Advanced Resources

  • David J. Malan offers lectures in the following areas of audio and video compression along with some basics in graphic formats. This lecture is available in the following formats to download: Streaming. Available in Flash, MP3 and QuickTime formats, along with jargon, slides, and transcript in PDF.

    Problem Set 5: Multimedia. Reinforce your understanding of the above topics in multimedia! Available in PDF.

  • Dominik Szopa has a website dedicated to Lossless Compression (Squeeze) which covers compression techniques such as Huffman, Adaptive Huffman, and LZW.

    This site also has applets to demonstrate the compression techniques.

  • Herong Yang has a free Cryptography Tutorials book which is a collection of notes and sample codes written by the author while he was learning cryptography technologies himself. It can be used as a tutorial guide for beginners.

 


Classroom Activities and Games: Basic Resources

  • CS Unplugged Activity 17 – Cryptographic Protocols

  • The Royal Institution UK and Microsoft Research together have produced the following activities:

    1. Information Salvation: The Odd Apple Out Challenge: an activity in Information Theory explaining the concept of compression for the classroom
    2. Keeping secrets secret: The process of protecting information is called cryptography, and here we explore cryptography in two ways. First, we’ll look at hidden pictures that only reveal themselves when you pair them up with their correct partner, or visual cryptography. Then we’ll take a look at how information on the internet is encrypted using clock

      arithmetic, a kind of maths that is really easy to do in one direction but almost impossible in reverse.

    3. Zero-knowledge games: These are called ‘zero-knowledge’ methods, because you can get an answer without

      ever finding out anything new about the important information. Here we provide two zero-knowledge games you can try with your friends at home or school. The first is one way of finding out if two people agree on a decision without either of them revealing what they actually decided! The second lets you work out the total of all your ages, without everyone finding out how old anyone else is.

    4. See also, games and tryouts related to these lectures at the interactive website
  • Computing Science Inside Workshop has an activity Zipping it Up which is a nice extension activity to this topic. This workshop questions why it has taken so long to introduce 3G mobile phones, identifying lack of bandwidth as a key issue. It explores the area of data compression and decompression - essential in any application where the bandwidth is low or storage is limited - and gets pupils working with the kinds of algorithms that underlie the Zip utility found on a PC. Note: You will need to apply and register in order to recieve the Workshop Pack for this activity.
  • NASA Space Math III has Correcting Bad Data Using Parity Bits. Students see how computer data is protected from damage by radiation glitches by using a simple error-detection method involving the parity bit. They will reconstruct an uncorrupted sequence of data by checking the eighth bit to see if the transmitted data word has been corrupted. By comparing copies of the data sent at different times, they reconstruct the uncorrupted data. A one-page teacher guide accompanies the one-page assignment.
  • ProQuest K-12 has an educational activity To Code or Not to Code where students will research different types of codes and ciphers, develop a code or cipher, and more.
    Note: This teacher plan was developed for research on the ProQuest site, but teachers here may use Wikipedia instead for student searches on the topics. Some alteration of the lesson will be necessary
  • StaySafeOnline has Cyberbullying Teaching Package. These free lessons are based on current research findings and best practices from the fields of cyber security, school violence prevention, and character education to impact behavioral change. Together, these materials offer schools the opportunity to begin a dialogue with students and build a sustained cyberbullying prevention campaign to continually remind the school community about safe, ethical online use.
  • Scholastic has a simple fun activity Create Your Own Coded Language to discover and encounter cryptology used in everyday lives. After discovering some uses and types of codes, students will create their own secret writing or coded messages, and develop a dictionary of eponyms.
  • AMNH has a fun activity Read with your Fingers, where kids run their fingers along the little bumps to read letters that form words and sentences. This activity lets you create braille messages and decode them.
  • Wolfram Demonstrations Project has the following useful demo activities in compression. Note: You will need to install the Wolfram CDF Player in order to use these activities. You can either download each demonstration or use your browser to run them:
    1. Audio File Size Calculator, which calculates the uncompressed file size, in bytes, required for a variety of digital audio file size output configurations
    2. See also Binary Run-Length Encoding, which splits data into runs of zeros and ones. A list of binary distinctions can then be encoded as a list of run-lengths
  • Wolfram Demonstrations Project has the following demo activities in cryptography you can give to students to try. Note: You will need to install the Wolfram CDF Player in order to use these activities. You can either download each demonstration or use your browser to run it
    1. Solve the Cryptoquote: Try your hand at decoding some famous quotes encoded using a substitution cipher. The person to whom the quote is attributed is encoded after the quote. Each cipher is a derangement of the letters of
      the alphabet, so that no letter stands for itself. If you need a hint to get started, the "show hint" button will randomly select a letter in the coded message and decode it for you.

    2. Solve the Cryptoquote Automatically: A cryptoquote is a puzzle, commonly found in newspapers, in which a substitution cipher is used to encrypt a famous quote. Here a brute force approach is taken to automatically decipher the encrypted
      text for 33 different puzzles listed in order of difficulty. The encrypted puzzle is dynamically updated as the solution progresses. Experiment with different solving strategies to enhance or degrade performance.

    3. Decoding the Arecibo Message: In 1974 a message was beamed from the Arecibo radio telescope towards a cluster of stars 25,000 light years distant in the constellation of Hercules. It consisted of 1679 binary digits transmitted in
      sequence. To read the message, the binary digits must be formed into a low resolution image on a two dimensional grid. But what sized grid should be used? Use the slider control to vary the number of columns in the grid and "decode" the Arecibo message.

    4. Learn the Radio Code: This Demonstration is one way to learn the International Civil Aviation Organization (ICAO) radio code. It lists several words and displays the conversion to the radio code. It can also speak the converted answer.
    5. Substitution Cipher Encoder: Substitution ciphers are one of the simplest forms of encryption, where replacement rules are provided that map each letter of the alphabet onto a different letter.
      This tool will generate randomly chosen keys that map the 26 letters of the English alphabet onto themselves. It also generates snippets of sample text from a range of English sources.

    6. Vernam Cipher: This Demonstration generates a random bit key for both sender and receiver of the Vernam cipher and provides a simple way to encryptand decrypt messages in various Unicode-supported languages.
    7. Hackers Language: Criminal hackers usually leave messages when breaking into a website or any system. The messages are written in a kind of code. It is not meant to be cryptography; the idea is just to show that
      it was left by a hacker. The language replaces some characters, for example: t to 7, B to 8, l to 1, i to !, s to z, and so on, but there is no strong rule. There are also legal hackers who program free software and open source projects such as Linux Kernel, KDE and Gnome user interfaces, Apache web server, and many others.

    8. RSA Encryption and Decryption: The RSA algorithm for public-key encryption was originated by Ron Rivest, Adi Shamir, and Leonard Adleman at MIT in 1977. Several similar methods had been proposed by earlier workers. The algorithm
      is based on the fact that it is far more difficult to factor a product of two primes than it is to multiply the two primes. Even the most powerful modern supercomputers would require more time than the age of the universe to factor a 400-digit number.

    9. Hill Cipher Encryption and Decryption: In a Hill cipher encryption, the plaintext message is broken up into blocks of length according to the
      matrix chosen. Each block of plaintext letters is then converted into a vector of numbers and is dotted with the matrix. The results are then converted back to letters and the ciphertext message is produced. For decryption of the ciphertext message, the inverse of the encryption matrix must be found. Once found, the decryption matrix is then dotted with each -block of ciphertext, producing the plaintext message.

    10. An Unforgettable Substitution Code: The characters in the two keywords give the beginning of the encryption alphabet completed by the remaining characters.
    11. Additive Cipher: The mono-alphabetic substitution cipher provides the simplest form of cryptography, where the cipher alphabet is simply a rearrangement of the plaintext alphabet. In an additive cipher, the cipher
      alphabet is a shift of the plaintext alphabet.

    12. Visual Encryption Pad: Only one position of the random mask will reveal clear text hidden in the cypher pad. The security of the code depends on a safe way to pass or keep the random mask. Application of the trivial
      rules {0->1, 1->0, 2->1} to the sum of clear text and random mask generates the cypher pad.

    13. Redundancy in Written Language: Languages have different levels of redundancy. Move the slider to remove increasing numbers of letters. Some languages remain readable even after removing a significant portion of the letters,
      while others become unreadable much sooner.

  • NCTM Illuminations has the following activities or resources:
    1. Check that Digit introduces learners to the concept of checking digits in barcodes and credit card numbers with complete lesson plan.
    2. Codes is an application that explains Cryptography
    3. Arithme-Tic-Toc where students will be introduced to modular arithmetic by first examining a five-hour analog clock and its mathematical properties. Then students will investigate patterns and relationships that exist in 12-hour addition and multiplication clock tables
    4. Code Crackers: Students begin an exploration of cryptology by first learning about two simple coding methods, the Caesar cipher and the Vigenere cipher. Students then use matrices and their inverses to create more sophisticated codes. See the units in Caeser Cipher and Vigenere Cipher 
  • PBS Kids Cyberchase has the following activities in code breaking. These activities are for elementary school students and therefore very easy for high school:
    1. Codename: Icky: You can use a code (a communication system that substitutes one thing for another) to send top secret messages as long as your code has an adjustable rule that can be reversed to read the message.
    2. Crack the Code the game to follow the above activity
  • WebRangers has the following activities of interest:
    1. George Washington's Secret Code. In this online interactive, learners decipher codes used by George Washington to safeguard messages during the American Revolution. Learners use a key to decode an excerpt from "Rules of Civility & Decent Behaviour in Company and Conversation," which Washington copied as a writing exercise when he was a teenager and historians believed influenced the development of his character.
    2. Semaphore: Talking with Flags
  • GK-12 at Harvard University has some useful resources and worksheets in Encryption. Description: Introduces students to some basic ciphers and the concept of encryption. Can be extended with a programming exercise in which one or both are implemented. Can also be extended with a discussion of public-key encryption works to provide the encryption we use online today. Note that the examples and problems given are best if they are customized to be phrases that are meaningful to the students in the class:
    1. Caesar Cipher Handout

    2. Vigenere Cipher Handout

  • CrypTool is is a free, open-source e-learning application, used worldwide in the implementation and analysis of cryptographic algorithms. It supports both contemporary teaching methods at schools and universities as well as awareness training for employees and civil servants.
  • CrypTool-Online is online version of the free e-learning program CrypTool . While CrypTool online is primarily intended for  studying  the fundamentals of classic ciphers, the download version of CrypTool is also suitable for working with longer texts and conducting high performance analyses on encrypted messages.
  • PBS' NOVA Online has the following resources available in codes and ciphers with worked out examples:
    1. Crack the Ciphers : offers three World War II-style ciphers of different levels of difficulty for you to try to break

    2. Send a Coded Message : offers an online version of an Enigma-like machine to encode your own message, then e-mail that message to a friend with instructions on how to decode it using a secret key.

    3. Decipher a Coded Message: How easy is it to crack a simple cipher? This feature lets you find out. There is a secret message encrypted using a cipher. The cipher's key is straightforward—each letter of the alphabet is represented by another letter.
    4. A Simple Cipher: lets you learn some of the tricks codebreakers use to solve ciphers, and use your new talents to make sense of what looks like a bunch of gibberish.

    5. Are Web Transactions Safe?: looks at all the ways encryption affects you, with a special emphasis on the Internet.

    6. Mind of a Codebreaker: led by Alan Turing, inventor of the computer, the codebreakers of Bletchley Park were a brilliant, quirky bunch who broke the Engima in large part by learning to think like the German codemakers themselves.

    7. How the Enigma Works: The Enigma looks roughly like a typewriter, but it is infinitely more complex, with fully 17,576 ring settings for each of 60 possible wheel orders—and that is just to set it up for use.



    Decoding Nazi Secrets: a television broadcast from November 9, 1999 offers some materials for teacher use which based on the program. Please note that the video is not required for using these activities:

    1. Classroom Activity: includes materials, lesson plans and answers

    2. Teaching Ideas from Other Teachers

    3. Complete Transcript of the television broadcast: can be used for research and further reading

    4. Send a Coded Message: an interactive online activity for students


    Melissa Salpietra has the following interactive online activities:

    1. Cryptography 101: an interactive activity that demonstrates different ways to make messages secret including transposition and substitution ciphers

    2. Send a Secret Message: an interactive activity that lets you write a note, encode it, and send it to a friend for decoding.

  • Frode Weierud has a collection of cipher machine simulators that can be downloaded for understanding how these machines work. For the complete list of simulators with sample screens and documentation please visit Enigma Variations: An Extended Family of Machines . These resources could be used for classroom tasks and teaching ideas at a senior school level.

  • Dirk Rijmenants has an entire website Cipher Machines and Cryptology with loads of resources in Cryptography. A great activity challenge of interest is the following challenge which could be used as teaching tools:

    1. Enigma Challenge: The Enigma cipher challenge gives you the chance to show your code breaking skills. Anyone, interested in the Enigma machine, can join the challenge.

    2. Cryptobox Challenge: The Crypto Box Challenge is a contest to decipher three scrambled pieces of text.
  • Rumkin has some useful applets students can try online for knowing how the different ciphers work in comparison with each other:
    1. Affine Similar to a Caesarian shift, but also adds in a multiplier to further scramble letters
    2. Atbash A very simplistic cipher where you change A into Z, B into Y, and so on.
    3. Baconian Used to hide a message within another message, by using different typefaces or other distinguishing characteristics.
    4. Base64 This is typically used to make binary data safe to transport as strictly text.
    5. Bifid Breaks information for each letter up and spreads it out in the encoded message. An easy and fairly secure pencil & paper cipher.
    6. Caesarian Shift Where ROT13 was based on you adding 13 to the letters, a Caesar cipher lets you add an arbitrary value. Again, you can do it with the cryptogram solver, but you can scroll through values of N pretty easily with this tool.
    7. Keyed Caesar Similar to a Caesar cipher, but you first alter the encoded alphabet with a word or phrase.
    8. Columnar Transposition Write a message as a long column and then swap around the columns. Read the message going down the columns. A simple cypher, but one that is featured on the Kryptos sculpture at the CIA headquarters.
    9. Double Transposition Because two is better than one. Used by the U.S. Army during World War II.
    10. Cryptogram Solver This helps you solve simple ciphers; the methods where you replace letter X with letter Y.
    11. Gronsfeld The exact same thing as a Vigenere cipher, but it uses numbers instead of a key word.
    12. Morse Code Once used to transmit messages around the world, this system can still be used in certain situations to send messages effectively when alternate mediums are not available
    13. Letter Numbers Replace each letter with the number of its position in the alphabet. A simple replacment method that is usually the first one taught to children and is still an effective way to obscure your message.
    14. One Time Pad A virtually uncrackable cipher that relies heavily upon a random source for an encryption key.
    15. Playfair This cipher uses pairs of letters and a 5x5 grid to encode a message. It is fairly strong for a pencil and paper style code.
    16. Railfence A mildly complicated one where you align letters on different rows and then squish the letters together in order to create your ciphertext.
    17. ROT13 A popular method of hiding text so that only people who actually take the time to decode it can actually read it. You swap letters; A becomes N, and N becomes A. It was quite popular on bulletin board systems and Usenet newsgroups. You can do it with the cryptogram solver also, if you make A=N, B=O, C=P, etc.
    18. Rotate This acts as though you are writing the letters in a rectangular grid and then rotating the grid to the left or right 90°.
    19. Skip To decode this, you count N characters, write down the letter, count forward N characters, write down the letter, etc. It is used for section 3 of the Kryptos.
    20. Substitution Substitute your plaintext letters with other letters, images, or codes. Includes two common pigpen ciphers and the Sherlock Holmes' Dancing Men cipher.
    21. Übchi A double columnar transposition cipher that uses the same key, but adds a number of pad characters. Used by the Germans in WWI.
    22. Vigenere A special cipher somewhat based on the Caesarian shift, but you change the value of N with each letter and it is all based on a passphrase. A pretty strong cipher for beginners, and one that can be done on paper easily.
    23. Keyed Vigenere This modified cipher uses an alphabet that is out of order. Two keys are used. One creates the alphabet, the second is the encoding passphrase. This was created to help decrypt the Kryptos sculpture.
    24. Vigenere Autokey Instead of repeating the password used in order to encrypt text, this uses the password once and then the plaintext. It is harder to break than if you were to just use the password to encrypt your message
  • Ralph Morelli, Trinity College has the following tools to understand Cryptography:
    1. Cryptogram Tool
    2. Cryptogram of The Week
    3. HcryptoJ (Historical cryptology in Java) is an extensible Java library for creating and anlyzing historical ciphers. HcryptoJ is suitable for novice and intermediate Java programmers who wish to write their own encryption engines. Includes source code and online documentation.
    4. CryptoToolJ is an extensible Java application program for creating and anlyzing historical ciphers. CryptoToolJ can be used as is to create the following kinds of ciphers: simple substitution, Caesar, transposition, Vigenere, affine, poly substitution, and Playfair. It contains cryptanalysis programs that automatically break most substitution, Caesar, affine, and Vigenere ciphers. CryptoToolJ has a plugin capability that enables you to write your own cipher engines and analyzers that can be added to CryptoToolJ without recompiling it. This download include HcryptoJ, plus source code and online documentation.
  • FFFBI has the Hencoder activity (intended for younger audiences, but still fun for all) where you type or paste a short message and Hencode it. Level Three means you'll read every third word to decode it (beginning with the third word). At Level Four, it would be every fourth word.

 

Classroom Activities and Games: Advanced Resources

 


Videos

  • Abdullah Seddiq (MIT Blossoms) has The Magic Picture: Steganography in Bitmap Files, a video with teacher guides and other resources. This video aims to connect many topics in computer science to reach the writing of an application that can do something useful in actual life. The student will get to know the concept of ciphering and hiding (Steganography in bitmap files), will have a glance at the American Standard Code for Information Interchange table "ASCII", will understand the structure of bitmap (BMP), and learn how color is stored.
  • eHowTech's YouTube Channel offers a video What is an Encryption? that explains that an encryption is basically an algorithm that any type of data can be run through, thus presenting a new version of the data. Discover how to write a decryption to pull the encryption back out with help from a software developer in this free video on encryption.
  • The Thomas Beale Cipher is a 10-minute award-winning film that tells the true legend of history's most challenging cipher. Professor White, cryptographer extraordinaire, is on the trail of the notoriously uncrackable Thomas Beale cipher—a century-old riddle hiding the location of a fortune in gold that has tormented its pursuers since inception. But White is not alone—shadowy forces are tight on his tail. The film contains 16 hidden messages that hold clues to the characters' secrets. Eight are fairly easy and require only a close eye. Six are moderately difficult using various encryption methods. Two are extremely difficult and will require a genius mind to decrypt.
  • Muhammad Aurangzeb (MIT Blossoms) has The Mathematics of Cryptography, a video and lesson plan where students will learn about the history of cryptography and they will also learn how powerful even a limited knowledge of mathematics can be as they work through the math used in cryptography. They will be involved in creating cryptography devices with pencils and will be exposed to increasingly more complex cryptography challenges.
  • Daniel J. Sturtevant (MIT Blossoms) has Building Cryptosystems, a video module with lesson plan where students will build three different devices for cryptography and will learn how to encrypt and decrytp messages.
  • Teachers' Domain has a video documentary on Luis von Ahn: Computer Scientist where you can learn about one of his most successful ideas—CAPTCHA—a test that humans can pass but computers cannot, which has been used to improve the security of Internet sites. Explore how he comes up with his innovative ideas, and how CAPTCHAs have been reinvented