A03: Crypto Treasure Hunt

ABBREVIATED 30-MINUTE VERSION

Overview

Time: 30 minutes
Format: Desk-only (no physical treasure hunt)
Points: 50
Group Size: 3-4 students

What's Different: This version eliminates the physical retrieval phase and provides substitution key hints upfront. All materials are in this single packet. Perfect for shorter class periods or online/hybrid learning.

Learning Objectives

Apply basic cryptographic decryption techniques
Understand hash functions for data verification
Practice simplified signature verification
Connect cryptography concepts to real-world applications

⏱️ Time Allocation:

0-10 minutes: Decrypt the message
10-25 minutes: Complete signature verification
25-30 minutes: Answer reflection questions

1Decryption Challenge

Encrypted Message

WKH FOBH PHVVDJH VDB:
"FUBRWR LV VHFXUH"

🔑 Cipher Key Hint

This is a Caesar Cipher: each letter is shifted by the same number of positions in the alphabet.

Hint: The shift value is 3. To decrypt, shift each letter backward 3 positions.

Example:

Encrypted	D	E	F
Decrypted	A	B	C

Your Decryption Work

Show your work here:

W → _____ K → _____ H → _____
F → _____ O → _____ B → _____
H → _____ (continue for remaining letters...)

Decrypted Message

THE CLUE MESSAGE SAYS: ""

2Signature Verification

Now that you've decrypted the message, verify the digital signature to ensure it's authentic.

📧 Clue Card Information

Imagine you retrieved a physical clue with this information:

Message (M): CRYPTO
Public Key: e = 7, n = 143
Signature (S): 42

Step 2A: Calculate Hash (H)

Hash the message by summing ASCII values and taking modulo n.

ASCII Values (Quick Reference):

Letter	ASCII	Letter	ASCII	Letter	ASCII
A	65	J	74	S	83
B	66	K	75	T	84
C	67	L	76	U	85
D	68	M	77	V	86
E	69	N	78	W	87
F	70	O	79	X	88
G	71	P	80	Y	89
H	72	Q	81	Z	90
I	73	R	82	0-9	48-57

Calculate the hash:

Character	ASCII Value
C
R
Y
P
T
O
Sum

Hash calculation:

H = mod 143 =

Step 2B: Verify Signature (V)

Apply the public key to the signature: V = S^e mod n

Calculate verification value:

S =
e =
n =

Step 1: Calculate S^e

Step 2: Calculate (S^e) mod n

mod =

Verification Value (V) =

Step 2C: Compare and Conclude

H (Hash) =
V (Verification) =

Are they equal?
☐ YES - Signature is VALID
☐ NO - Signature is INVALID/FORGED

Conclusion: The signature is

3Reflection Questions

Question 1: Encryption Security

What would happen if someone intercepted your encrypted message during transmission? How does encryption protect the information?

Question 2: Public Key Cryptography

Explain how the public key allows anyone to verify the signature without revealing the private key. Why is this important for security?

Question 3: Real-World Applications

Name two real-world applications that use digital signatures and signature verification (like what you just practiced).

Team Information

Team Member Name	Role in Activity	Signature

Grading Summary (50 Points)

Component	Points	Score
Correct Decryption (with work shown)	15
Hash Calculation (H) - Correct	8
Signature Verification (V) - Correct	8
Proper Comparison and Conclusion	4
Reflection Question 1	5
Reflection Question 2	5
Reflection Question 3	5
TOTAL	50

📝 Instructor Notes

Setup time: 5 minutes (just print packets)

No physical setup required - all materials in this single packet

Ideal for:

Short class periods (30-40 minutes)
Online/hybrid classes
Makeup assignments
Review sessions before exams

Answer Key:

Decrypted message: "THE CLUE MESSAGE SAYS: CRYPTO IS SECURE"
Hash (H): C=67, R=82, Y=89, P=80, T=84, O=79, Sum=481, H=481 mod 143 = 52
Verification (V): 42^7 mod 143 = 52
Result: H=V (52=52), signature is VALID

Abbreviated Version | 30 Minutes | All-in-One Packet | Page 1 of 1