Ciphering a sentence
About this lesson
A cipher is a message that has been written in such a way (encoded) that it is unreadable by others. In this lesson, students will use mapping to encode a sentence. Students will work with a partner to create an algorithm that describes the encryption process. They will also examine encoded and decoded messages to recognize patterns to help decode messages and develop strategies to decompose the problem.
Year band: 3-4, 5-6Curriculum Links Assessment
Links with Digital Technologies Curriculum Area
|Processes and Production Skills||3-4||
Define simple problems and describe and follow a sequence of steps (algorithms) needed to solve them (ACTDIP010)
|Processes and Production Skills||5-6||
Design, modify and follow simple algorithms involving sequences of steps, branching, and iteration (repetition) (ACTDIP019)
Links with English Curriculum Area
|Language: Phonics and word knowledge||3-4||
Understand how to apply knowledge of letter-sound relationships, syllables, and blending and segmenting to fluently read and write multisyllabic words with more complex letter patterns (ACELA1826)
Understand how to use phonic knowledge to read and write multisyllabic words with more complex letter combinations, including a variety of vowel sounds and known prefixes and suffixes (ACELA1828)
|Language: Phonics and word knowledge||5-6||
Understand how to use phonic knowledge to read and write less familiar words that share common letter patterns but have different pronunciations (ACELA1829)
Understand how to use phonic knowledge and accumulated understandings about blending, letter-sound relationships, common and uncommon letter patterns and phonic generalisations to read and write increasingly complex words (ACELA1830)
Student self-assessment task
Consider the commands used to move the Bee-Bot. Students complete a simple cloze activity to evaluate understanding:
Bee-Bots travel ______cm each time they move one step. The arrow keys at the front and back are used to program the Bee-Bot to move __________ or _____________. The arrow keys on each side are used to program the Bee-Bot to move __________ or ____________. I can start a new program by pressing the ___________ button.
- Learning hook: Forming a strategy (10 minutes)
- Learning demonstration: Create the alphabet mapping (25 minutes)
- Learning construction: Encode sentences (20 minutes)
- Learning reflection: Analysis and reflection (20 minutes)
- Additional information and resources
- Additional Resources
Learning hook: Forming a strategy (10 minutes)
In this activity, students will think about strategies for sending messages that are guaranteed to be private.
Pretend that you want to send a private message to a friend. The only way you can deliver the message is to write it on a board that is observable by anyone who passes by. What could you and your friend do to ensure that you are the only people who can understand the message?
Learning demonstration: Create the alphabet mapping (25 minutes)
In this activity, students write rules for mapping and reordering the alphabet for encoding messages to create an algorithmic cipher.
Learning construction: Encode sentences (20 minutes)
In this activity, students will use the algorithm mappings from the Learning demonstration section to encode sentences.
Divide students in groups of two and tell them the following:
- Think of a simple message you would like to send to your partner.
- Encode it three times: first use just Alphabet Mapping #1, then use just Alphabet Mapping #2, and then use both mappings from the previous activity.
For example, if the sentence is:
We drove to the gym.
Using the Alphabet Mapping #1, we find each letter of the sentence in the second row of the table created in Activity 1. We replace the letter with the corresponding number in the first row.
Please note that one must place letter breaks (the character “_”) and separate each word by a blank space. In this example, the encoded sentence is:
23 9 3 7 4 22 9 20 4 20 12 9 11 25 17
Learning reflection: Analysis and reflection (20 minutes)
In this activity, students will decompose their own ciphers, how ciphers might be represented with a computer program, and some of the issues in breaking and designing ciphers (recognizing patterns).
Tell students to discuss and record answers to the following questions in their journals with their partners.
- Which Alphabet Mapping (1 or 2) is easier to use to encode a message?
- Are the rules used for Alphabet Mapping #1 clear and easy to understand? How could you improve the rules?
- Is your new rule for Alphabet Mapping #2 clear and easy to understand? How could you improve your rule?
- How would you implement your cipher in a computer program? Could you break down the problem and write the sequence of steps (an algorithm) that describes the process?
- Imagine that another person gives you an encoded message and you do not know the mapping tables. How would you go about deciphering or decoding the sentences? What patterns would you look for to help you discover the one-to-one mapping?
- If someone wants to come up with a cipher that is very difficult to for others to decode, what are some of the strategies that he or she should consider to break down the problem (decomposition)?
Additional information and resources
|Algorithm Design||Creating an ordered series of instructions for solving similar problems|
|Pattern Recognition||Observing patterns and regularities in data|
|Decomposition||Breaking down data, processes or problems into smaller, manageable parts|
Computational Thinking concepts
|Term||Definition||For Additional Information|
|Encryption||The process of encoding messages or information in such a way that only authorized parties can read it||http://en.wikipedia.org/wiki/Encryption|
|Decryption||The process of decoding messages or information in such a way that only authorized parties can read it||http://en.wikipedia.org/wiki/Encryption|
|Cipher||An encoded/encrypted message||http://en.wikipedia.org/wiki/Cipher|
|Algorithm||A step-by-step set of operations performed to solve a problem||http://en.wikipedia.org/wiki/Encryption|