This experiment teaches you how to analyze and decrypt shift cipher (Caesar cipher) ciphertext using various cryptanalysis techniques. Follow these steps to master the shift cipher:

STEP 1: Understanding the Challenge (PART I)

Start by examining the given ciphertext in PART I - Decryption Challenge:

• You'll see a challenge ciphertext that needs to be decrypted
• The challenge number and total challenges are displayed
• You can click "🔄 Next Ciphertext" to cycle through different challenge ciphertexts
• Each challenge has a different plaintext and shift key

Example: The first challenge shows haahjr ha khdu which should decrypt to attack at dawn using shift 7.

STEP 2: Analysis and Exploration (PART II)

Use the analysis tools provided in PART II - Analysis Workspace:

• 📊 Frequency Analysis:

  • Click this button to analyze letter frequencies in the current ciphertext
  • Compare cipher letter frequencies with common English letter patterns
  • Look for the most frequent cipher letter (might correspond to 'E')
  • Use the frequency hints to estimate the shift value

• 🔍 Test All Shifts:

  • Automatically try all possible shift values (0-25)
  • Look for meaningful English words and phrases in the results
  • Results marked with ⭐ indicate particularly promising decryptions
  • Use this for brute force cryptanalysis

• Rough Work Area:

  • Use the large text area to make notes and record observations
  • Keep track of promising shift values and partial decryptions
  • Document your cryptanalysis process

• 🗑️ Clear: Clear your rough work area when needed

STEP 3: Practice and Verification (PART III)

Use the encryption/decryption tool in PART III - Shift Cipher Simulator:

• For Practice:

  • Enter any plaintext in the text area
  • Select a shift value (0-25) from the dropdown
  • Click "🔒 Encrypt ↓" to see the ciphertext result
  • Click "🔓 Decrypt ↑" to reverse the process

• For Verification:

  • Enter your suspected plaintext from the challenge
  • Set the shift value you think is correct
  • Encrypt to see if it matches the original challenge ciphertext
  • This confirms your analysis is correct

STEP 4: Submit Your Solution (PART IV)

Once you've identified the correct plaintext and shift key:

• Enter Solution: Type the decrypted plaintext in the solution text area
• Select Key: Choose the corresponding shift key from the dropdown
• Check Answer: Click "🎯 Check my answer!" to verify your solution
• Review Feedback:
  • Correct answers show success message and verification in Part III
  • Incorrect answers provide detailed hints and guidance
  • Use the feedback to improve your analysis

STEP 5: Learn from Verification

When you get the correct answer:

• The system automatically sets up Part III with your solution
• You can see exactly how the plaintext encrypts to the challenge ciphertext
• This reinforces your understanding of how the shift cipher works
• Click "🔄 Next Ciphertext" to try more challenges

Example Walkthrough:

Let's decrypt the cipher text "KRZ DUH BRX" step by step:

Step 1: Observe the ciphertext pattern Step 2: Use "Test All Shifts" in Part II:

• For k=0: "krz duh brx" (no meaning)
• For k=1: "jqy ctg aqw" (no meaning)
• For k=2: "ipx bsf zpv" (no meaning)
• For k=3: "how are you" ⭐ (meaningful!)

Step 3: Verify in Part III by entering "how are you" with shift 3 Step 4: Submit "how are you" and key "3" in Part IV Step 5: Receive confirmation and move to next challenge

Tips for Success:

• Start with frequency analysis for longer ciphertexts
• Use "Test All Shifts" for quick brute force analysis
• Look for common English words like "the", "and", "you"
• Practice with Part III to understand the cipher mechanics
• Pay attention to the detailed feedback in Part IV

Using the Simulation Tools:

• You can use the "Test All Shifts" button in PART II to automatically perform this brute force analysis
• The frequency analysis tool can help identify patterns that suggest the correct shift value
• The manual encryption/decryption tool in PART III allows you to verify specific hypotheses
• The feedback system in PART IV provides immediate verification of your solutionext in PART I of the simulation page. You can click "Next Ciphertext" to get different challenge ciphertexts to decrypt.

STEP 2 : Use the analysis tools provided in PART II to help with your cryptanalysis:

• Frequency Analysis (📊): Analyze letter frequencies in the current ciphertext to identify patterns
• Test All Shifts (🔍): Automatically try all possible shift values (0-25) to find meaningful text
• Rough Work Area: Use the text area to make notes, record your observations, and keep track of promising decryptions
• Clear Button (🗑️): Clear your rough work area when needed

STEP 3 : Use the encryption/decryption tool in PART III to manually test specific shift values:

• Enter text in the plaintext area
• Select a shift value (0-25) from the dropdown
• Click "Encrypt" to see the ciphertext result
• Click "Decrypt" to reverse the process
• This helps you understand how the shift cipher works and test your hypotheses

STEP 4 : Once you've identified the correct plaintext and shift key through analysis:

• Enter the decrypted plaintext in the PART IV solution text area
• Select the corresponding shift key from the dropdown
• Click "Check my answer!" to verify your solution
• The feedback area will show whether your answer is correct and provide hints if needed

STEP 5 [OPTIONAL] : Verify your understanding by using PART III to encrypt your solution plaintext with your discovered key to confirm it produces the original ciphertext.

An Example:

Let us say we have a cipher text "KRZ DUH BRX" generated by a shift cipher. We carry out the brute force attack as follows:

For k=0:

cipher text: K R Z D U H B R X
          plain text: k r z d u h b r x
          

For k=1:

cipher text: K R Z D U H B R X
          plain text: j q y c t g a q w
          

For k=2:

cipher text: K R Z D U H B R X
          plain text: i p x b s f z p v
          

For k=3:

cipher text: K R Z D U H B R X
          plain text: h o w a r e y o u
          

For k=3, we obtain a meaningful plain text namely how are you and hence we are done.