Safe Signals Intro Slides SAFE SIGNALS
Part 1: Trust on an Open Network
[System] INITIALIZING SECURITY_V1...
The Paper Trail
"Imagine passing a note to a friend across a crowded room. Every person who touches that note could potentially read it."
The Internet is just a series of "hands" passing your digital notes from one point to another. How do we know they aren't looking?
Insecure Packet
The Man-in-the-Middle
Sender (Alice)
The Interceptor
MitM!
Receiver (Bob)
A MitM Attack occurs when a third party secretly relays and possibly alters the communication between two parties who believe they are directly communicating.
Where does this happen?
Public Wi-Fi
Coffee shops and airports are prime spots for rogue hotspots that "sniff" your data.
ISP Nodes
Your data passes through dozens of routers owned by different companies before it reaches its goal.
Proxies
Malicious software can install a proxy on your device to intercept all browser traffic.
THE ESSENTIAL QUESTION
How can we communicate privately and securely over a public network that is accessible to everyone?
Time to simulate the threat...
Note Snatcher Activity Sheet Note Snatcher Activity
UNIT: SAFE SIGNALS // SESSION 1.1
Name:
Date:
Objective
Analyze how unencrypted data can be intercepted, read, and modified as it travels across an open network through a simulated Man-in-the-Middle (MitM) attack.
Phase 1: Direct Transmission
During the simulation, you will pass three different "packets" (notes) to your partner. For each packet, record what happened.
Packet # Original Message Sent Result Packet 01 Example: "Meet at lunch at 12" Delivered Intact
|
| Packet 02 | | |
| Packet 03 | | |
Phase 2: The MitM Attack
Critical vulnerability
Now, an Interceptor is placed in the middle. They will receive your notes before your partner. Answer the following after the simulation:
1. Was your message intercepted? If so, did the Interceptor change anything?
2. How did the Interceptor’s actions change the outcome of the message (e.g., wrong meeting time, private secret revealed)?
Network Forensics
Loss of Confidentiality
When a third party reads your private message.
Did this happen in your simulation? How do you know?
Loss of Integrity
When a third party alters the data in your message.
Did this happen? What was the "false" information delivered?
Intercept Simulation Guide Intercept Simulation Guide
Teacher Resource // Lesson 1.1
Simulation Setup
Materials Needed
Small slips of paper (20-30 per group)
Note Snatcher Activity Sheets
Red markers (for the Interceptor)
Group Roles
Divide students into groups of 3:1. Alice (Sender): Originates the message.2. Bob (Receiver): The intended destination.3. Eve (Interceptor): The Man-in-the-Middle.
Execution Stages
1
Stage 1: The "Direct" Line
Alice passes a note directly to Bob. This represents a local, physical connection. There is no risk here. Alice and Bob record the success of the delivery on their sheets.
2
Stage 2: The Network Path
Now, Alice and Bob must sit 5-10 feet apart. They must pass the note through the "Internet" (Eve). Eve receives the note, reads it, and passes it to Bob. Bob should not know Eve is reading it yet.
3
Stage 3: The Active Attack
Alice sends a message with a specific instruction (e.g., "Bring me a blue pen"). Eve intercepts it and changes the message (e.g., "Bring me a red pen") before Bob gets it. Bob performs the action based on the changed note.
Discussion Questions
"How would Bob know the message was changed? Is there a signature or 'seal' that was broken?"
"In the digital world, who are the 'Eves' that sit between us and our bank websites?"
"If Alice and Bob spoke a secret language Eve didn't know, would that help? (Tease Lesson 2: Encryption)"
CSTA 3A-NI-05: Explain how security measures protect personal and public data. Estimated Time: 45 Minutes
Symmetric Secrets Slides SYMMETRIC SECRETS
Part 2: The Shared Key
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
What is Encryption?
The process of encoding a message so that it can only be read by the sender and the intended recipient.
Plaintext
Ciphertext
"HELLO" → "KHOOR"
Symmetric = One Key
Sender
Shared Secret Key
Receiver
In Symmetric Encryption , both the sender and the receiver use the exact same key to encrypt and decrypt the data.
The Caesar Cipher
Named after Julius Caesar, who used it for military secrets.
SHIFT 3
PLAIN: A B C D E F G H I
CIPHER: D E F G H I J K L
If you know the shift (the key), the secret is easy to unlock. But what if you don't?
The Distribution Problem
How do Alice and Bob agree on a secret key in the first place without an Interceptor stealing it during the exchange?
Wait... if the network is unsecure, sending the key is unsecure too!
Cipher Wheel Reference Cipher Wheel Tool
SYMMETRIC ENCRYPTION // CAESAR SHIFT GENERATOR
Assembly Instructions
Carefully cut out both circles (the large outer wheel and the small inner wheel).
Place the small wheel on top of the large wheel, centering them perfectly.
Use a brass fastener (brad) through the center point to connect them so the inner wheel can rotate.
To encrypt with a shift of 3, rotate the inner wheel so 'D' (inner) aligns with 'A' (outer).
A C E G I K M O Q S U W B D F H J L N P R T V X Z Y
Outer Wheel: Plaintext
A D G J M P S V B C E F H I K L N O Q R T U W X Z Y
Inner Wheel: Ciphertext
SAFE SIGNALS // NETWORK SECURITY WORKSHOP // DESIGNED FOR 9TH GRADE COMPUTER SCIENCE
Cipher Cracker Worksheet Cipher Cracker
SYMMETRIC ENCRYPTION WORKSHOP
Agent Name:
Date:
Mission 01: Scramble
Use your Caesar Wheel to encrypt the following messages. Remember to rotate the inner wheel to the specified shift key.
KEY: SHIFT 5 Example: A → F
Plaintext
NETWORKS ARE OPEN
Ciphertext
KEY: SHIFT 13 This is a ROT13 cipher.
Plaintext
THE KEY IS HIDDEN
Ciphertext
Mission 02: Crack
You intercepted a message on the network! Use the known key to decrypt it.
KEY: SHIFT 7
INTERCEPTED DATA
LUAX OHJR KVALK
DECRYPTED MESSAGE
The Crypto-Dilemma
"If you want to send an encrypted message to a friend across the country, how do you securely tell them which Shift Key you are using without the Interceptor finding out?"
Asymmetric Armor Slides ASYMMETRIC ARMOR
Part 3: Public & Private Keys
The Lockbox Analogy
Imagine a mailbox that anyone can drop a letter into, but only one person has the key to open it.
"I can give everyone in the world a lock that only I have the key for."
PRIVATE KEY
The Power of the Pair
PUBLIC KEY
Shared with the whole world. Anyone can use it to ENCRYPT (lock) data for you.
0x7F4B2A9...
PRIVATE KEY
Kept secret by you. Only you can use it to DECRYPT (unlock) the data.
0xE1A99C2...
How it Works Together
Sender
Sender uses Receiver's Public Key to lock the data.
Receiver uses their own Private Key to unlock it.
Receiver
The "shared secret" problem is solved because the Private Key never travels over the network.
Encryption Speed Check
Symmetric
Fast and efficient for large amounts of data (like streaming video), but has the "Secret Key Exchange" problem.
FAST
Asymmetric
Secure for key exchange without meeting, but mathematically complex and much slower for large files.
SECURE
Solution: Use Asymmetric to exchange a Symmetric key!
Key Pair Organizer Key Pair Organizer
ASYMMETRIC ENCRYPTION // MAPPING THE FLOW
Name:
Public Key
Think of this as an open padlock you give to everyone.
What is its main purpose?
Private Key
Think of this as the physical key that stays in your pocket.
What is its main purpose?
The Encryption Handshake
ALICE (Sender)
BOB (Receiver)
Bob sends his______________________
Alice uses the key to lock the message. Even if an Interceptor steals it, they can't open it because they don't have the ______________________ .
Bob uses his______________________
The "Intercept" Check
If Eve (the Interceptor) is watching the network, she sees Bob send his Public Key to Alice. Why is this not a problem for security?
Lockbox Logic Guide Lockbox Logic Guide
Teacher Facilitation // Lesson 3.1
The Hook Challenge
The Problem:
"Alice wants to send a secret message in a lockbox to Bob across the country. Alice has a padlock and a key. Bob has a different padlock and a different key. However, they cannot send physical keys through the mail because an Interceptor will copy them."
"How can Bob open the box without Alice ever sending him her key?"
The "Double-Lock" Solution
1
Alice puts the message in the box and locks it with her padlock . She mails it to Bob.
2
Bob receives the locked box. He cannot open it. He adds his own padlock to the box. It now has two locks. He mails it back to Alice.
3
Alice receives the box with two locks. She removes her lock with her key. She mails the box back to Bob.
4
Bob receives the box. It only has his lock on it. He opens it with his key . Success!
Digital Connection
This conceptual flow demonstrates how we can achieve secure communication without ever exchanging secret keys on an open network.
// This is the basis of
Facilitation Tips
Let them struggle: Present the problem and give groups 5 minutes to brainstorm solutions before revealing the "Double-Lock" method.Physical Props: If possible, use two real padlocks and a small box to demonstrate the steps.The Interceptor: Ask: "What did the Interceptor see during each mailing?" (Answer: A locked box, then a double-locked box, then a locked box again. Never the message.)
CSTA 3A-NI-04: Evaluate the reliability of network systems. Estimated Time: 30-40 Minutes
Trusted Traffic Slides Trusted Traffic
Part 4: Digital Certificates & HTTPS
https://www.secure-bank.com
The "S" Matters
PORT 80
HTTP
HyperText Transfer Protocol. Data is sent as Plaintext . Anyone in the middle can read your password.
NOT SECURE
PORT 443
HTTPS
HTTP Secure . Uses SSL/TLS encryption. Data is scrambled before it leaves your computer.
ENCRYPTED
The Digital Handshake
Your Browser
1. "Hello! Can we talk securely?"
2. "Sure! Here is my ID (Certificate)."
3. "I trust you! Let's start encrypting."
Web Server
What is a Certificate?
It's like a Passport for a website. It proves the site is who they say they are.
Verified by a Certificate Authority (CA)
Contains the site's Public Key
Includes an Expiration Date
Certificate
ISSUED TO: google.com
ISSUED BY: Google Trust Services
VALID FROM: 2026-01-01
VALID UNTIL: 2026-04-01
PK: 0x4f 0xa1 0x22 0xb3 0x09 0x98 0x22 ...
Certificate Warnings
If a site's certificate is expired or "self-signed," your browser will scream at you. NEVER ignore this warning on a banking or shopping site!
⚠️ Your connection is not private
Site Safety Investigation Site Safety Investigation
Cyber-Security Forensics // Lab 4.1
Investigator:
Date:
Lab Instructions
Open a web browser. Click the icon next to the URL. Select "Connection is secure" → "Certificate is valid" (or similar wording depending on your browser) to find the technical details of the site's identity.
Task 01: The Verified ID
Choose a popular website (e.g., Google, Amazon, your school's site) and record its certificate details below.
Website URL
https://
Issued To (Common Name)
Issued By (Certificate Authority)
Example: DigiCert, Let's Encrypt
Valid Until (Expiration Date)
Public Key Type & Length
Example: RSA 2048-bit
Serial Number (Last 4 Digits)
Task 02: Spot the Scam
Scenario: You receive an email from "Support@SecureBank.com " telling you to login and check your balance. You click the link and see this in the address bar:
http://www.secure-bank.login-portal.net/login.html
Identify two red flags with this connection:
Red Flag 1
Red Flag 2
Why is a Certificate Authority (CA) necessary? What would happen if anyone could just create their own "Verified" certificate for Google.com?
Secure Lock Exit Ticket Exit Ticket: Secure Lock
Name:
Lesson 4.1 // HTTPS & Certificates
1. Which of the following is the primary purpose of an SSL/TLS Certificate?
To make the website load faster on mobile devices.
To verify the website's identity and provide a public key for encryption.
To block hackers from attacking the server's firewall.
2. In your own words, what does the "S" in HTTPS stand for, and what does it actually change about the data being sent?
Exit Ticket: Secure Lock
Name:
Lesson 4.1 // HTTPS & Certificates
1. Which of the following is the primary purpose of an SSL/TLS Certificate?
To make the website load faster on mobile devices.
To verify the website's identity and provide a public key for encryption.
To block hackers from attacking the server's firewall.
2. In your own words, what does the "S" in HTTPS stand for, and what does it actually change about the data being sent?
Perimeter Patrol Slides Perimeter Patrol
Part 5: Firewalls & Network Defense
The Network Gatekeeper
A Firewall is a security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules.
It acts as a barrier between a trusted network and an untrusted network (like the Internet).
Rules of Engagement
Firewalls look at "Packet Headers" to make decisions:
IP Address
"Block all traffic coming from this specific malicious server."
Port Number
"Allow traffic on Port 443 (HTTPS), but block Port 21 (FTP)."
Protocol
"Only allow web browsing traffic; block file transfers."
The Rule Table
ACTION PROTOCOL PORT REASON ALLOW TCP 443 Secure Web Traffic DENY UDP Any Unknown Protocol ALLOW TCP 80 Standard Web (Warning)
"Default Deny": Most secure firewalls block EVERYTHING except what is explicitly allowed.
Gatekeeper Protocol
Now it's your turn. Can you handle the pressure of managing a high-traffic perimeter without letting a single threat through?
Live Sim
Gatekeeper Protocol Activity Gatekeeper Protocol
Perimeter Defense Simulation // Activity 5.1
Firewall Admin:
Objective
Review incoming "data packets" and apply firewall rules to decide which should be ALLOWED or DENIED .
Current Security Policy
ACTIVE RULES:
1. ALLOW Protocol: TCP on Port 443 (HTTPS)
2. ALLOW Protocol: TCP on Port 80 (HTTP)
3. DENY Source IP: 192.168.1.50 (Known Botnet)
4. DENY Protocol: UDP (Any Port)
5. DEFAULT: DENY everything else.
Traffic Log
Packet ID Source IP Protocol Port Action (Circle) #001 172.16.0.5 TCP 443 ALLOW DENY #002 192.168.1.50 TCP 80 ALLOW DENY #003 10.0.0.12 UDP 53 ALLOW DENY #004 172.16.0.22 TCP 21 ALLOW DENY #005 8.8.8.8 TCP 443 ALLOW DENY
Analysis:
In packet #002, the Source IP was blocked even though the Port (80) is normally allowed. Why is it important for a firewall to check both the Port and the Source IP?
Network Guard Quiz Network Guard Quiz
Safe Signals // Final Evaluation
Student Name:
Score:
/ 50
01 // Encryption Methods
1. Matching: Draw a line to the correct definition.
A. Symmetric Encryption
B. Asymmetric Encryption
C. Man-in-the-Middle
Uses a pair of keys (Public and Private).
An attack where data is intercepted.
Uses the same secret key for both parties.
2. Why do we typically use Asymmetric Encryption only at the beginning of a session (the handshake) instead of for the entire video stream or file download?
02 // The Web Perimeter
3. When you visit https://www.google.com , your browser checks the site's certificate. What is ONE piece of information that the certificate proves to your browser?
4. Multiple Choice: Which of these would a Firewall most likely use to block a known "Bad Actor" from another country?
Checking the site's font-style.
Filtering by Source IP Address.
Reading the user's browser history.
Checking the file size of an image.
03 // Synthesis
5. Explain the "Defense in Depth" approach. Why isn't a firewall alone enough to protect your private credit card data when shopping online?
END OF ASSESSMENT // SIGNAL_SECURED_VERSION_1.0
