Secret Codes: A Cipher
Python Programming 2 Grades 9–12 3-day lesson 25 deliverables Teach students to hide a message in Python with a shift cipher and to crack one by brute force. Students use a printed table to encrypt and decrypt notes, then write functions that run a loop one character at a time. They use ord() and chr(), wrap letters around past Z with % 26 and decrypt by shifting the opposite way.
● Instant download · Lifetime access · Editable & print-ready
Print + digitalPDF, PowerPoint, Word & Google
Answer keysA key for every page
Built-in assessmentExit tickets + lesson quiz
45-minute daysEvery day planned and timed
Short coding levels practice this lesson in CodeGrove, our code lab that runs in the browser. Students write the program, run it and check it, with no account and nothing to install. Use them with the lesson or as practice later.
See the levelsWhat does this lesson cover?
Students often treat encryption as magic and miss why the key matters. This lesson has them encrypt by hand first, then crack a short message by trying every shift. They see why a longer key is harder to crack.
The lab on Day 2 and the quiz task on Day 3 run online in CodeGrove, our in-browser code lab, so students need a computer or tablet on those days. The Cipher Lab level practices writing functions that encrypt, decrypt and crack a shift cipher, one character at a time. CodeGrove is free, with no accounts, sign-ins or installs.
Cipher Lab
Students write functions in CodeGrove that encrypt a message with a shift cipher and crack a secret by brute force.
Everything that's included
00 Start Here
- READ FIRST: every file in the lesson and when you use it
- Teacher Guide and Pacing: the plan for each day, what to print and how to grade
- Skills map: which standards each day teaches
01 Present
- One editable PowerPoint deck for all three days, 23 slides, with speaker notes
- Slide script: the speaker notes, printed
- Bell ringers: a short warm-up for each day
02 Student Handouts
- Guided notes: one packet for all three days, in PDF and editable Word. Students fill in the blanks during the slides, with the word bank on the page
- Vocab slip: the lesson's words and what they mean, on one page
03 Labs
- Cipher Lab: students write functions in CodeGrove that encrypt a message with a shift cipher and crack a secret by brute force
04 Activities
- Cipher Table: students encrypt, decrypt and crack short messages with a printed shift table, on paper with computers closed
- Quiz task: students shift a typed word in CodeGrove, working alone, and then take the lesson quiz on paper
05 Assessment
- Exit tickets: quick questions that show who needs more help
- Lesson quiz: 8 multiple-choice questions and 2 written answers about all three days, on paper
06 Answer Keys
- 5 answer key files: a key for each day (its bell ringer, notes and exit ticket) and the activity and lab keys, plus the quiz key
Digital: Google Forms™ + Google Slides™
- 4 Google Forms™ of the exit tickets and the quiz, ready to copy into your Drive
- The multiple choice grades itself, and you grade the written answers
- A Google Slides™ copy of the deck, with the same slides and speaker notes, for Google Classroom™
Online: CodeGrove
- In CodeGrove: the lab on Day 2 (Cipher Lab) and the quiz task on Day 3, on a computer or tablet for each student
- Free to use, with no accounts, sign-ins or installs
Why teachers love this lesson
Cracking a cipher shows why keys matterA shift cipher has a small number of keys. Students try every one by brute force and read the hidden message.
A loop turns the idea into codeStudents write functions that handle one character at a time and wrap the count around past Z. Shifting the opposite way decrypts.
Print and digitalEvery page is a print-ready PDF, and the Google Forms™ and Google Slides™ let you teach the same lesson in Google Classroom™.
Real online labsStudents write and run real Python in CodeGrove, our in-browser code lab, on a computer or tablet, with no accounts or installs.
A key for every pageEvery day has its own answer key, and every written question has a sample answer and what to look for.
Every day fits a 45-minute classEach day's plan is timed activity by activity against real reading and writing speeds.
What Teachers Say
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How do I get the files after I buy?
Instant download right after checkout: PowerPoint and Word files you can edit, print-ready PDFs, and links that copy the Google Forms™ and Google Slides™ into your Drive.
Can I buy the whole unit or course instead?
Yes. This lesson is part of the Unit 2 bundle and the complete Python Programming 2 course. Both cost less than buying the lessons one at a time.
Is this AP Computer Science?
No. It is a full-year, non-AP second course in Python for grades 9 to 12. For AP, see our AP Computer Science A and AP CSP courses.
What should students know before this lesson?
Students know ord(), chr(), %, and how to build new text one letter at a time.
Do students need computers?
Yes, on the CodeGrove days. Each student needs a computer or tablet that's online, and CodeGrove needs no account or install. The bell ringers, notes, exit tickets and quiz are on paper.
What formats are the files in?
Every page is a print-ready PDF. The slides are an editable PowerPoint and the guided notes an editable Word file. The exit tickets and the quiz also come as Google Forms™, and the deck as Google Slides™.
Which standards does it cover?
Written for Florida's Intermediate Programming course (9007220). The skills map in the lesson shows which standards each day teaches.