Cryptanalysis is the study of methods to obtain the meaning of encrypted information without access to the secret key, evaluating the security of cryptographic systems.

What is Cryptanalysis?

Cryptanalysis is the science of breaking codes and ciphers, analyzing vulnerabilities in cryptographic algorithms to improve their security or compromise systems.

Types of Attacks

By Available Information

  • Ciphertext Only: Only ciphertext
  • Known Plaintext: Known plaintext
  • Chosen Plaintext: Chosen plaintext
  • Chosen Ciphertext: Chosen ciphertext

By Objective

  • Key Recovery: Key recovery
  • Plaintext Recovery: Plaintext recovery
  • Distinguishing: Distinguishing encryption from random
  • Forgery: Signature forgery

By Method

  • Brute Force: Brute force
  • Dictionary Attack: Dictionary attack
  • Frequency Analysis: Frequency analysis
  • Differential Cryptanalysis: Differential cryptanalysis

Classical Attacks

Brute Force

  • Description: Try all possible keys
  • Complexity: O(2^n) where n is key length
  • Countermeasures: Long keys, rate limiting
  • Example: Attack on DES (2^56 keys)

Frequency Analysis

  • Description: Analyze patterns in ciphertext
  • Application: Simple substitution ciphers
  • Method: Compare letter frequencies
  • Countermeasures: Complex ciphers, padding

Dictionary Attack

  • Description: Try common words as keys
  • Application: Weak passwords
  • Method: Predefined word list
  • Countermeasures: Complex passwords, salt

Modern Attacks

Differential Cryptanalysis

  • Description: Analyze differences in plaintext pairs
  • Application: Block ciphers (DES, AES)
  • Method: Look for patterns in differences
  • Complexity: Less than brute force

Linear Cryptanalysis

  • Description: Look for linear relationships between bits
  • Application: Block ciphers
  • Method: Linear approximations
  • Complexity: Known-plaintext attack

Side-Channel Attacks

  • Timing Attacks: Timing attacks
  • Power Analysis: Power consumption analysis
  • Electromagnetic: Electromagnetic analysis
  • Acoustic: Acoustic analysis

Specific Attacks

RSA Attacks

  • Factorization: Factor modulus n
  • Timing Attack: Measure operation time
  • Power Analysis: Analyze power consumption
  • Fault Injection: Fault injection

AES Attacks

  • Differential Cryptanalysis: Differential cryptanalysis
  • Linear Cryptanalysis: Linear cryptanalysis
  • Biclique Attack: Biclique attack
  • Related-Key Attack: Related-key attack

ECC Attacks

  • Discrete Logarithm: Discrete logarithm problem
  • Side-Channel: Side-channel attacks
  • Fault Injection: Fault injection
  • Invalid Curve: Invalid curves

Cryptanalysis Tools

General Software

  • Cryptool: Educational tool
  • OpenSSL: Cryptographic library
  • GnuPG: OpenPGP implementation
  • John the Ripper: Password cracker

Specialized Tools

  • Hashcat: Hash cracker
  • Aircrack-ng: WiFi cracker
  • Wireshark: Traffic analysis
  • Metasploit: Exploitation framework

Research Tools

  • SageMath: Mathematical software
  • Magma: Computational algebra system
  • PARI/GP: Computational algebra system
  • GAP: Computational algebra system

Attack Implementation

Brute Force Attack

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import itertools
import hashlib

def brute_force_attack(target_hash, charset, max_length):
    """Brute force attack on hash"""
    for length in range(1, max_length + 1):
        for attempt in itertools.product(charset, repeat=length):
            password = ''.join(attempt)
            if hashlib.sha256(password.encode()).hexdigest() == target_hash:
                return password
    return None

# Usage example
target = "5d41402abc4b2a76b9719d911017c592"  # MD5 of "hello"
charset = "abcdefghijklmnopqrstuvwxyz"
result = brute_force_attack(target, charset, 5)
print(f"Password found: {result}")

Frequency Analysis

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from collections import Counter
import string

def frequency_analysis(ciphertext):
    """Frequency analysis in ciphertext"""
    # Count frequencies
    freq = Counter(ciphertext.lower())
    
    # English frequencies
    english_freq = {
        'e': 12.7, 't': 9.1, 'a': 8.2, 'o': 7.5, 'i': 7.0,
        'n': 6.7, 's': 6.3, 'h': 6.1, 'r': 6.0, 'd': 4.3,
        'l': 4.0, 'c': 2.8, 'u': 2.8, 'm': 2.4, 'w': 2.4,
        'f': 2.2, 'g': 2.0, 'y': 2.0, 'p': 1.9, 'b': 1.3,
        'v': 1.0, 'k': 0.8, 'j': 0.15, 'x': 0.15, 'q': 0.10,
        'z': 0.07
    }
    
    # Calculate correlation
    correlation = 0
    for char in string.ascii_lowercase:
        if char in freq and char in english_freq:
            correlation += freq[char] * english_freq[char]
    
    return correlation

# Usage example
ciphertext = "hello world"
correlation = frequency_analysis(ciphertext)
print(f"Correlation: {correlation}")

Timing Attack

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import time
import statistics

def timing_attack(secret, guess):
    """Simple timing attack"""
    start_time = time.time()
    
    # Simulate comparison that takes more time with more matches
    for i in range(min(len(secret), len(guess))):
        if secret[i] != guess[i]:
            break
        time.sleep(0.001)  # Simulate delay
    
    end_time = time.time()
    return end_time - start_time

def find_secret(secret, charset, length):
    """Find secret using timing attack"""
    result = ""
    
    for pos in range(length):
        times = {}
        
        for char in charset:
            guess = result + char + "0" * (length - pos - 1)
            times[char] = timing_attack(secret, guess)
        
        # Character with highest time is probably correct
        best_char = max(times, key=times.get)
        result += best_char
    
    return result

Countermeasures

Algorithm Design

  • Avalanche Effect: Small change = large change
  • Non-linearity: Non-linear operations
  • Confusion: Confusion in design
  • Diffusion: Information diffusion

Secure Implementation

  • Constant Time: Constant time
  • Random Padding: Random padding
  • Key Derivation: Key derivation
  • Secure Random: Secure random numbers

Attack Protection

  • Rate Limiting: Rate limiting
  • Lockout: Lockout after attempts
  • Monitoring: Attack monitoring
  • Intrusion Detection: Intrusion detection

Legitimate Applications

Security Evaluation

  • Penetration Testing: Penetration testing
  • Vulnerability Assessment: Vulnerability assessment
  • Red Team Exercises: Red team exercises
  • Security Audits: Security audits

Academic Research

  • Algorithm Analysis: Algorithm analysis
  • Security Research: Security research
  • Cryptographic Protocols: Cryptographic protocols
  • New Attack Methods: New attack methods

Defense Development

  • Security Hardening: Security hardening
  • Attack Mitigation: Attack mitigation
  • Security Training: Security training
  • Best Practices: Best practices
  • Authorization: Authorization for testing
  • Scope: Testing scope
  • Documentation: Documentation of findings
  • Responsible Disclosure: Responsible disclosure

Professional Ethics

  • White Hat: Ethical hacking
  • Responsible Disclosure: Responsible disclosure
  • Privacy Protection: Privacy protection
  • Harm Prevention: Harm prevention
  • AES - Cryptanalysis target algorithm
  • RSA - Cryptanalysis target algorithm
  • ECC - Cryptanalysis target algorithm
  • Hash Functions - Cryptanalysis target algorithms
  • HSM - Device that protects against cryptanalysis
  • CISO - Role that oversees cryptanalysis
  • General Cybersecurity - Discipline that includes cryptanalysis
  • Security Breaches - Result of successful cryptanalysis
  • Attack Vectors - Cryptanalysis as a vector
  • Incident Response - Process that includes cryptanalysis
  • SIEM - System that detects cryptanalysis
  • SOAR - Automation that responds to cryptanalysis
  • EDR - Tool that protects against cryptanalysis
  • Firewall - Device that can detect cryptanalysis
  • VPN - Connection that can be a cryptanalysis target
  • Dashboards - Visualization of cryptanalysis metrics
  • Logs - Cryptanalysis attempt logs

References