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Labs / Caesar Shift Decoder

  • Daily Challenge
  • Released 10 Sep 2025

🏛️ Can you crack Julius Caesar's secret military code?

Ancient Roman generals relied on this ingenious cipher to protect their most sensitive battle plans and strategic communications. 🛡️ What stumped enemy cryptographers for centuries now challenges modern code breakers to uncover hidden messages through mathematical precision and pattern analysis. 🔍 Master the techniques that shaped the foundation of modern cryptography and prove your skills against this timeless encryption method! ⚔️

1
Flags
1
Points
Daily Challenge
Pro Exclusive
Start Lab Environment
~1-2 min setup
AWS dedicated
Private instance
Industry standard
Daily Challenge

🏛️ Caesar Shift Decoder - Complete Solution

Objective: Decode the Caesar cipher by determining the correct shift value and revealing the hidden flag.
🔍 Step 1: Identify the Encrypted Message

The challenge presents this encrypted flag:

Encrypted: 364m41i4-hjk6-4002-904i-6186mkijl3m3

Notice that numbers and hyphens remain unchanged, while only letters are encrypted.

🔍 Step 2: Determine the Shift Value

The correct shift value is 7. This means each letter was moved forward 7 positions in the alphabet during encryption.

Key Insight: To decrypt, we need to shift each letter BACKWARD by 7 positions.
🔍 Step 3: Manual Decryption Process

Let's decode each letter step by step:

PositionEncryptedShift Back 7Decrypted
4thmm(-7) = ff
7thii(-7) = bb
10thhh(-7) = aa
11thjj(-7) = cc
12thkk(-7) = dd
17thii(-7) = bb
22ndmm(-7) = ff
23rdkk(-7) = dd
24thii(-7) = bb
25thjj(-7) = cc
26thll(-7) = ee
28thmm(-7) = ff
29thmm(-7) = ff
🔍 Step 4: Complete Decryption

Applying the shift of -7 to all encrypted letters:

Encrypted: 364m41i4-hjk6-4002-904i-6186mkijl3m3
Decrypted: 364f41b4-acd6-4002-904b-6186fdbce3f3
🔍 Step 5: Verification

The decrypted result is a valid UUID format containing only hexadecimal characters (0-9, a-f):

  • Pattern: 8-4-4-4-12 characters separated by hyphens ✓
  • Characters: Only 0-9 and a-f (valid hexadecimal) ✓
  • Format: Proper UUID structure ✓
🎯 Final Answer
Flag: 364f41b4-acd6-4002-904b-6186fdbce3f3
🔍 Alternative Methods

You could also solve this using:

// JavaScript in browser console
let cipher = '364m41i4-hjk6-4002-904i-6186mkijl3m3';
let decoded = cipher.replace(/[a-z]/g, char =>
  String.fromCharCode((char.charCodeAt(0) - 97 - 7 + 26) % 26 + 97)
);
console.log(decoded); // 364f41b4-acd6-4002-904b-6186fdbce3f3
📚 Learning Points
  • Shift Value: Caesar cipher used shift of 7 positions
  • Decryption: Reverse the encryption by shifting backward
  • Pattern Recognition: Valid UUID format confirms correct decryption
  • Brute Force: Only 25 possible shifts make testing feasible
  • Character Preservation: Numbers and symbols remain unchanged