9. Cryptanalysis exercises to reinforce theoretical concepts

Cryptanalysis Exercises

• Cryptanalysis involves analyzing cryptographic systems to understand their vulnerabilities and weaknesses.
• Frequency Analysis: Frequency analysis is a classical cryptanalysis technique used to break substitution ciphers by analyzing the frequency of letters or symbols in the ciphertext.
• Brute Force Attacks: Brute force attacks involve systematically checking all possible keys until the correct one is found. They are commonly used to break weak encryption schemes or short keys.
• Differential Cryptanalysis: Differential cryptanalysis is a modern cryptanalysis technique used to break block ciphers by analyzing the difference between pairs of plaintexts and their corresponding ciphertexts.
• Side-Channel Attacks: Side-channel attacks exploit information leaked through physical implementations of cryptographic systems, such as power consumption, timing, or electromagnetic radiation.
• Fault Injection Attacks: Fault injection attacks involve introducing faults into the cryptographic system, such as voltage spikes or clock glitches, to manipulate its behavior and reveal secret information.

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Laboratory Activities

Lab 1: Frequency Analysis

In this lab, we'll perform frequency analysis on a given ciphertext to decipher a substitution cipher.

def frequency_analysis(ciphertext):
    frequencies = {}
    for char in ciphertext:
        if char.isalpha():
            char = char.lower()
            frequencies[char] = frequencies.get(char, 0) + 1
    
    sorted_frequencies = sorted(frequencies.items(), key=lambda x: x[1], reverse=True)
    return sorted_frequencies

# Example ciphertext
ciphertext = "Lxuo rdb qdph lv brxu dqvzhu lq vwulqjxqj phvvdjh."
frequencies = frequency_analysis(ciphertext)

print("Frequency Analysis Results:")
for char, freq in frequencies:
    print(char, ":", freq)

Lab 2: Brute Force Attack

In this lab, we'll perform a brute force attack on a Caesar cipher to decrypt a given ciphertext.

def caesar_decrypt(ciphertext, shift):
    plaintext = ""
    for char in ciphertext:
        if char.isalpha():
            if char.islower():
                decrypted_char = chr(((ord(char) - ord('a') - shift) % 26) + ord('a'))
            else:
                decrypted_char = chr(((ord(char) - ord('A') - shift) % 26) + ord('A'))
            plaintext += decrypted_char
        else:
            plaintext += char
    return plaintext

# Example ciphertext
ciphertext = "Wklv lv d whvw phvvdjh."
for shift in range(1, 26):
    plaintext = caesar_decrypt(ciphertext, shift)
    print("Shift:", shift, " Decrypted Text:", plaintext)

Lab 3: Differential Cryptanalysis

In this lab, we'll perform a differential cryptanalysis attack on a simplified block cipher to break its encryption.

def differential_cryptanalysis(ciphertexts, plaintexts):
    # Implementing differential cryptanalysis algorithm
    n = len(ciphertexts[0]) // 2
    pairs = [(ciphertexts[i] ^ ciphertexts[j], plaintexts[i] ^ plaintexts[j]) for i in range(len(ciphertexts)) for j in range(i+1, len(ciphertexts))]
    count = {}
    for c, p in pairs:
        if c in count:
            count[c] += 1
        else:
            count[c] = 1
    return max(count, key=count.get)

# Example ciphertexts and plaintexts
ciphertexts = [0b101010, 0b110011, 0b010101, 0b011001]
plaintexts = [0b001100, 0b110000, 0b101010, 0b000011]

key_guess = differential_cryptanalysis(ciphertexts, plaintexts)
print("Key Guess:", key_guess)

Lab 4: Side-Channel Attack

In this lab, we'll perform a simple side-channel attack by measuring the power consumption of a cryptographic device during encryption.

def encrypt_with_power_consumption(plaintext, key):
    # Simulate encryption with power consumption measurement
    # This is a placeholder for actual code
    return "Ciphertext"

# Example usage
plaintext = "Hello, world!"
key = "secret_key"
ciphertext = encrypt_with_power_consumption(plaintext, key)

print("Ciphertext with Power Consumption:", ciphertext)

Lab 5: Fault Injection Attack

In this lab, we'll perform a fault injection attack by introducing faults into the execution of a cryptographic algorithm to observe its behavior.

def encrypt_with_fault_injection(plaintext, key):
    # Simulate encryption with fault injection
    # This is a placeholder for actual code
    return "Ciphertext"

# Example usage
plaintext = "Hello, world!"
key = "secret_key"
ciphertext = encrypt_with_fault_injection(plaintext, key)

print("Ciphertext with Fault Injection:", ciphertext)