SHA-224 Security Analysis

| Security Property    | SHA-224  | SHA-256  | SHA-384  | SHA-512  | SHA-1    | MD5      |
|----------------------|----------|----------|----------|----------|----------|----------|
| Collision Resistance | 2^112    | 2^128    | 2^192    | 2^256    | Broken   | Broken   |
| Preimage Resistance  | 2^224    | 2^256    | 2^384    | 2^512    | ~2^160   | ~2^128   |
| Second Preimage      | 2^224    | 2^256    | 2^384    | 2^512    | ~2^160   | ~2^128   |
| Status as of 2025    | Secure   | Secure   | Secure   | Secure   | Broken   | Broken   |
| NIST Status          | Approved | Approved | Approved | Approved | Legacy   | Not app. |

| Year | Researchers                | Attack Type        | Rounds Broken | Complexity      |
|------|----------------------------|-------------------|---------------|-----------------|
| 2005 | Wang, Yu, Yin              | Differential      | 31/64         | 2^229           |
| 2008 | Mendel et al.              | Boomerang         | 34/64         | 2^137           |
| 2009 | Nikolić and Biryukov       | Rotational        | 46/64         | 2^153           |
| 2013 | Khovratovich et al.        | Biclique          | 45/64         | 2^222           |
| 2019 | Song and Qin                | Differential      | 47/64         | 2^208           |
| 2022 | Chen and Wang              | Deep-Learning     | 48/64         | 2^195           |

import struct
import hashlib

class SHA224Simulator:
    """SHA-224 simulator for demonstrating length extension attacks"""
    
    def __init__(self, h_state):
        # Initialize with the internal state values (7 words for SHA-224)
        self.h_state = h_state
        
    def pad_message(self, msg_len_bytes):
        """Generate padding for a message of the given length"""
        # SHA-224 uses the same padding as SHA-256
        bit_len = msg_len_bytes * 8
        # Add 1 bit followed by zeros
        padding = b'\x80'
        # Pad with zeros until the length is congruent to 56 (mod 64)
        padding += b'\x00' * ((56 - (msg_len_bytes + 1) % 64) % 64)
        # Append original message length as a 64-bit big-endian integer
        padding += struct.pack('>Q', bit_len)
        return padding
        
    def update(self, message):
        """Update the hash state with the given message"""
        # In a real implementation, this would process the message through
        # the SHA-224 compression function. For demonstration, we use hashlib.
        
        # In a real attack, we would implement the SHA-224 compression function
        # to continue from the known internal state
        pass
        
    def hexdigest(self):
        """Get the hexadecimal digest representation"""
        # Convert the state to a byte string and then to hex
        return ''.join(f'{h:08x}' for h in self.h_state)

def length_extension_attack(original_hash, original_msg_len, append_data):
    """Demonstrates a length extension attack on SHA-224"""
    # Parse the original hash to get the internal state
    h_state = []
    for i in range(0, len(original_hash), 8):
        h_word = int(original_hash[i:i+8], 16)
        h_state.append(h_word)
    
    # Create a simulator initialized with the parsed state
    simulator = SHA224Simulator(h_state)
    
    # Calculate the padding that would have been applied to the original message
    original_padding = simulator.pad_message(original_msg_len)
    
    # In a real implementation, we would now run the append_data through the
    # compression function continuing from the known state
    
    # For demonstration, we'll use hashlib to get the expected result
    # This simulates what an attacker would compute
    m = hashlib.sha224()
    # Original message (unknown to attacker) + its padding + append_data
    unknown_msg = b'A' * original_msg_len  # Placeholder, content doesn't matter
    m.update(unknown_msg + original_padding + append_data)
    extended_hash = m.hexdigest()
    
    return {
        "original_hash": original_hash,
        "extended_hash": extended_hash,
        "padding_hex": original_padding.hex(),
        "new_data_hex": append_data.hex(),
        "forged_suffix": original_padding + append_data
    }

# Example usage
original_hash = "d14a028c2a3a2bc9476102bb288234c415a2b01f828ea62ac5b3e42f"  # SHA-224("secret-data")
original_length = 11  # Length of "secret-data"
append_data = b"malicious-suffix"

result = length_extension_attack(original_hash, original_length, append_data)
print("Length Extension Attack Demonstration:")
print(f"Original hash: {result['original_hash']}")
print(f"Extended hash: {result['extended_hash']}")
print(f"This is the hash of 'secret-data||padding||malicious-suffix'")
print(f"An attacker could compute this without knowing 'secret-data'")
print(f"Padding used (hex): {result['padding_hex']}")
print(f"Appended data (hex): {result['new_data_hex']}")
print(f"Total forged suffix (hex): {result['forged_suffix'].hex()}")

/**
 * Constant-time comparison of SHA-224 hashes to prevent timing attacks
 * This is a critical security measure when verifying hashes
 */
#include 
#include 
#include 

/* Insecure comparison - vulnerable to timing attacks */
int insecure_compare(const unsigned char *a, const unsigned char *b, size_t len) {
    // Early return reveals information about where mismatch occurred
    for (size_t i = 0; i < len; i++) {
        if (a[i] != b[i]) {
            return 0; // Not equal
        }
    }
    return 1; // Equal
}

/* Secure constant-time comparison */
int secure_compare(const unsigned char *a, const unsigned char *b, size_t len) {
    unsigned char result = 0;
    
    // Always process all bytes regardless of mismatches
    for (size_t i = 0; i < len; i++) {
        result |= a[i] ^ b[i];  // XOR will be 0 only if bytes are equal
    }
    
    // Convert result to 0 or 1 in constant time
    // This technique prevents timing variations due to conditional branching
    return 1 & ((result - 1) >> 8);
}

/* Verify a SHA-224 hash in constant time */
int verify_sha224_hash(const unsigned char expected[28], const unsigned char actual[28]) {
    return secure_compare(expected, actual, 28);
}

/* Example usage */
void example() {
    // Example SHA-224 hashes (28 bytes each)
    unsigned char hash1[28] = {
        0xd1, 0x4a, 0x02, 0x8c, 0x2a, 0x3a, 0x2b, 0xc9,
        0x47, 0x61, 0x02, 0xbb, 0x28, 0x82, 0x34, 0xc4,
        0x15, 0xa2, 0xb0, 0x1f, 0x82, 0x8e, 0xa6, 0x2a,
        0xc5, 0xb3, 0xe4, 0x2f
    };
    
    unsigned char hash2[28] = {
        0xd1, 0x4a, 0x02, 0x8c, 0x2a, 0x3a, 0x2b, 0xc9,
        0x47, 0x61, 0x02, 0xbb, 0x28, 0x82, 0x34, 0xc4,
        0x15, 0xa2, 0xb0, 0x1f, 0x82, 0x8e, 0xa6, 0x2a,
        0xc5, 0xb3, 0xe4, 0x2f
    };
    
    // Verify in constant time
    int result = verify_sha224_hash(hash1, hash2);
    
    // The comparison time is independent of where/whether a mismatch occurs
}

| Language   | Recommended Library             | Notes                                |
|------------|--------------------------------|--------------------------------------|
| C/C++      | OpenSSL, LibreSSL, or Botan    | Widely audited, FIPS-validated       |
| Java       | java.security.MessageDigest    | Standard library implementation      |
| JavaScript | Web Crypto API or noble-hashes | Avoid older JS implementations       |
| Python     | hashlib                        | Standard library using OpenSSL       |
| Rust       | RustCrypto's sha2 crate        | Memory-safe implementation           |
| Go         | crypto/sha256                  | Standard library (supports SHA-224)  |
| .NET/C#    | System.Security.Cryptography   | Standard library implementation      |

const crypto = require('crypto');

// GOOD: Using HMAC for authentication
function secureAuthenticate(message, key) {
  return crypto.createHmac('sha224', key)
    .update(message)
    .digest('hex');
}

// GOOD: Constant-time comparison
function secureCompare(hashA, hashB) {
  // Node.js crypto provides a constant-time comparison function
  return crypto.timingSafeEqual(
    Buffer.from(hashA, 'hex'),
    Buffer.from(hashB, 'hex')
  );
}

// GOOD: Using SHA-224 for integrity verification
function verifyIntegrity(data, expectedHash) {
  const actualHash = crypto.createHash('sha224')
    .update(data)
    .digest('hex');
  
  return secureCompare(actualHash, expectedHash);
}

// GOOD: Proper key derivation
function deriveKey(password, salt) {
  // Use PBKDF2 with SHA-224 and many iterations
  return crypto.pbkdf2Sync(
    password,
    salt,
    100000, // High iteration count
    28,     // SHA-224 output size in bytes
    'sha224'
  ).toString('hex');
}

// BAD: Don't do this for password storage
function insecurePasswordHash(password) {
  // Too fast, no salt, vulnerable to rainbow tables
  return crypto.createHash('sha224')
    .update(password)
    .digest('hex');
}

// BAD: Don't do this for message authentication
function insecureAuthentication(message, key) {
  // Vulnerable to length extension attacks
  return crypto.createHash('sha224')
    .update(key + message)
    .digest('hex');
}

// BAD: Don't use regular comparison
function insecureCompare(hashA, hashB) {
  // Vulnerable to timing attacks
  return hashA === hashB;
}

Original message hashing:
┌────────┐       ┌────────┐       ┌────────┐
│        │       │        │       │        │
│   IV   │─────▶ │  Hash  │─────▶ │ State  │─────▶ H(M)
│        │       │Function│       │        │
└────────┘       └────────┘       └────────┘
                      ▲
                      │
                 ┌────────┐
                 │Message M│
                 │(unknown│
                 │to      │
                 │attacker)│
                 └────────┘

Length extension attack:
┌────────┐       ┌────────┐       ┌────────┐
│ Derived│       │        │       │  New   │
│state   │─────▶ │  Hash  │─────▶ │ State  │─────▶ H(M||padding||X)
│from H(M)│       │Function│       │        │
└────────┘       └────────┘       └────────┘
                      ▲
                      │
                 ┌────────┐
                 │Attacker's│
                 │extension │
                 │data (X)  │
                 └────────┘

require 'openssl'

class MessageAuthenticator
  def initialize(key)
    @key = key
  end
  
  # VULNERABLE: Simple SHA-224 with message prepended by key
  def vulnerable_authenticate(message)
    digest = OpenSSL::Digest.new('sha224')
    digest.update(@key)
    digest.update(message)
    digest.hexdigest
  end
  
  # SECURE: Using HMAC-SHA224
  def secure_authenticate(message)
    OpenSSL::HMAC.hexdigest('sha224', @key, message)
  end
  
  # SECURE: Using envelope method (key at both ends)
  def envelope_authenticate(message)
    digest = OpenSSL::Digest.new('sha224')
    digest.update(@key)   # Key prefix
    digest.update(message)
    digest.update(@key)   # Key suffix
    digest.hexdigest
  end
  
  # SECURE: Double-hashing
  def double_hash_authenticate(message)
    inner_hash = OpenSSL::Digest.new('sha224')
    inner_hash.update(@key)
    inner_hash.update(message)
    inner_digest = inner_hash.digest
    
    outer_hash = OpenSSL::Digest.new('sha224')
    outer_hash.update(inner_digest)
    outer_hash.hexdigest
  end
  
  # SECURE: Using truncation
  def truncated_authenticate(message, length=16)
    hmac = OpenSSL::HMAC.hexdigest('sha224', @key, message)
    hmac[0...length]  # Truncate to specified length
  end
  
  # Constant-time comparison
  def secure_compare(a, b)
    return false if a.bytesize != b.bytesize
    result = 0
    
    a.bytes.zip(b.bytes) do |x, y|
      result |= x ^ y
    end
    
    result == 0
  end
end

# Example usage
authenticator = MessageAuthenticator.new('secret_key_12345')
message = 'Important data that needs authentication'

# Generate authentication codes
vulnerable_mac = authenticator.vulnerable_authenticate(message)  # DON'T USE THIS
secure_mac = authenticator.secure_authenticate(message)         # RECOMMENDED
envelope_mac = authenticator.envelope_authenticate(message)     # ALSO GOOD
double_mac = authenticator.double_hash_authenticate(message)    # ALSO GOOD

puts "HMAC-SHA224: #{secure_mac}"
puts "Envelope method: #{envelope_mac}"
puts "Double hash: #{double_mac}"

# Secure verification
is_valid = authenticator.secure_compare(
  secure_mac,
  authenticator.secure_authenticate(message)
)
puts "Valid message: #{is_valid}"

| Algorithm   | Classical Security | Quantum Security | Recommendation for Long-term Use |
|------------|-------------------|-----------------|----------------------------------|
| MD5        | Broken            | Broken          | Do not use                       |
| SHA-1      | Broken            | Broken          | Do not use                       |
| SHA-224    | 112 bits          | ~75 bits        | Consider alternatives for 2030+  |
| SHA-256    | 128 bits          | ~85 bits        | Acceptable for most applications |
| SHA-384    | 192 bits          | ~128 bits       | Strong quantum resistance        |
| SHA-512    | 256 bits          | ~170 bits       | Very strong quantum resistance   |
| SHA3-224   | 112 bits          | ~75 bits        | Consider alternatives for 2030+  |
| SHA3-256   | 128 bits          | ~85 bits        | Acceptable for most applications |
| SHAKE128   | 128 bits          | ~85 bits        | Acceptable for most applications |
| SHAKE256   | 256 bits          | ~170 bits       | Very strong quantum resistance   |

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.HexFormat;

/**
 * A crypto-agile hash implementation that allows easy migration
 * between different hash algorithms as quantum computing advances
 */
public class QuantumResistantHash {
    
    // Hash algorithm levels
    public enum SecurityLevel {
        STANDARD,       // Current standard (SHA-224)
        HIGH,           // Higher security (SHA-384)
        QUANTUM,        // Quantum resistant (SHA-512)
        FUTURE_PROOF    // Multiple algorithms combined
    }
    
    private SecurityLevel level;
    
    public QuantumResistantHash(SecurityLevel level) {
        this.level = level;
    }
    
    /**
     * Computes a hash based on the selected security level
     */
    public String hashData(byte[] data) throws NoSuchAlgorithmException {
        switch (level) {
            case STANDARD:
                return computeHash(data, "SHA-224");
                
            case HIGH:
                return computeHash(data, "SHA-384");
                
            case QUANTUM:
                return computeHash(data, "SHA-512");
                
            case FUTURE_PROOF:
                // Combine multiple hash algorithms for defense in depth
                String sha512 = computeHash(data, "SHA-512");
                String sha3_256 = computeHash(data, "SHA3-256");
                
                // Combine hashes
                MessageDigest finalDigest = MessageDigest.getInstance("SHA-256");
                finalDigest.update(sha512.getBytes());
                finalDigest.update(sha3_256.getBytes());
                byte[] combinedHash = finalDigest.digest();
                
                return bytesToHex(combinedHash);
                
            default:
                throw new IllegalArgumentException("Unknown security level");
        }
    }
    
    private String computeHash(byte[] data, String algorithm) throws NoSuchAlgorithmException {
        MessageDigest digest = MessageDigest.getInstance(algorithm);
        byte[] hashBytes = digest.digest(data);
        return bytesToHex(hashBytes);
    }
    
    private String bytesToHex(byte[] bytes) {
        return HexFormat.of().formatHex(bytes);
    }
    
    /**
     * Upgrades the security level when needed
     */
    public void upgradeSecurityLevel(SecurityLevel newLevel) {
        if (newLevel.ordinal() < this.level.ordinal()) {
            throw new IllegalArgumentException("Cannot downgrade security level");
        }
        this.level = newLevel;
    }
    
    // Example usage
    public static void main(String[] args) {
        try {
            String message = "Data to be protected against quantum attacks";
            byte[] data = message.getBytes();
            
            // Start with standard security
            QuantumResistantHash hasher = new QuantumResistantHash(SecurityLevel.STANDARD);
            System.out.println("Standard security hash: " + hasher.hashData(data));
            
            // Later upgrade to quantum-resistant level
            hasher.upgradeSecurityLevel(SecurityLevel.QUANTUM);
            System.out.println("Quantum-resistant hash: " + hasher.hashData(data));
            
            // Future-proof for maximum security
            hasher.upgradeSecurityLevel(SecurityLevel.FUTURE_PROOF);
            System.out.println("Future-proof hash: " + hasher.hashData(data));
            
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
    }
}

HASH FUNCTION MIGRATION PLANNING FRAMEWORK

Phase 1: Assessment
- Inventory all hash function uses across the organization
  ├── Application code
  ├── Configuration files
  ├── Databases
  ├── API integrations
  ├── Digital signatures
  ├── Certificates
  └── Authentication systems

- For each use case, document:
  ├── Current algorithm (SHA-224)
  ├── Security requirements
  ├── Expected lifetime
  ├── Migration difficulty
  └── Business impact of changes

Phase 2: Prioritization Matrix
                Low Impact  |  Medium Impact  |  High Impact
                ------------------------------------
Low Urgency    |     3     |       4       |      5
Medium Urgency |     2     |       3       |      4
High Urgency   |     1     |       2       |      3

Phase 3: Technical Approaches
- Parallel Implementations
  └── Run both old and new hash functions during transition period

- Hash Extensibility
  └── Design to support multiple hash algorithms via configuration

- Versioning
  └── Include algorithm identifier with hash values

- Database Schema Updates
  └── Extend field sizes to accommodate larger hash values

Phase 4: Implementation Timeline
- Immediate (0-6 months)
  └── High urgency items, easy changes, new development

- Short-term (6-18 months)
  └── Medium urgency items, moderate difficulty

- Medium-term (18-36 months)
  └── Low urgency, high complexity items

- Long-term monitoring
  └── Ongoing cryptographic review process

<?php
/**
 * A cryptographically agile hashing system that facilitates
 * easy migration between hash algorithms
 */
class AgileHashManager {
    // Supported algorithms with their respective identifiers and output sizes
    private static $supportedAlgorithms = [
        'SHA224' => ['id' => 1, 'size' => 28, 'function' => 'sha224'],
        'SHA256' => ['id' => 2, 'size' => 32, 'function' => 'sha256'],
        'SHA384' => ['id' => 3, 'size' => 48, 'function' => 'sha384'],
        'SHA512' => ['id' => 4, 'size' => 64, 'function' => 'sha512'],
        'SHA3-256' => ['id' => 5, 'size' => 32, 'function' => 'sha3-256'],
    ];
    
    // Current default algorithm
    private $defaultAlgorithm;
    
    public function __construct($defaultAlgorithm = 'SHA224') {
        if (!array_key_exists($defaultAlgorithm, self::$supportedAlgorithms)) {
            throw new InvalidArgumentException("Unsupported algorithm: {$defaultAlgorithm}");
        }
        $this->defaultAlgorithm = $defaultAlgorithm;
    }
    
    /**
     * Update the default hash algorithm for new hashes
     */
    public function setDefaultAlgorithm($algorithm) {
        if (!array_key_exists($algorithm, self::$supportedAlgorithms)) {
            throw new InvalidArgumentException("Unsupported algorithm: {$algorithm}");
        }
        $this->defaultAlgorithm = $algorithm;
    }
    
    /**
     * Compute a hash with the default algorithm
     */
    public function hash($data) {
        return $this->hashWithAlgorithm($data, $this->defaultAlgorithm);
    }
    
    /**
     * Compute a hash with a specific algorithm
     */
    public function hashWithAlgorithm($data, $algorithm) {
        if (!array_key_exists($algorithm, self::$supportedAlgorithms)) {
            throw new InvalidArgumentException("Unsupported algorithm: {$algorithm}");
        }
        
        $algo = self::$supportedAlgorithms[$algorithm];
        $hash = hash($algo['function'], $data, true); // Raw binary output
        
        // Format: [1-byte algorithm ID][N-bytes hash value]
        $result = chr($algo['id']) . $hash;
        
        // Return as hex string for storage/transmission
        return bin2hex($result);
    }
    
    /**
     * Verify data against a stored hash
     */
    public function verify($data, $storedHash) {
        // Convert hex to binary
        $binaryHash = hex2bin($storedHash);
        
        // Extract algorithm ID (first byte)
        $algorithmId = ord($binaryHash[0]);
        
        // Find algorithm by ID
        $algorithm = null;
        foreach (self::$supportedAlgorithms as $algo => $details) {
            if ($details['id'] === $algorithmId) {
                $algorithm = $algo;
                break;
            }
        }
        
        if ($algorithm === null) {
            throw new RuntimeException("Unknown algorithm ID: {$algorithmId}");
        }
        
        // Extract the hash value (remaining bytes)
        $hashValue = substr($binaryHash, 1);
        
        // Compute a new hash with the same algorithm
        $algo = self::$supportedAlgorithms[$algorithm];
        $computedHash = hash($algo['function'], $data, true);
        
        // Constant-time comparison
        return hash_equals($hashValue, $computedHash);
    }
    
    /**
     * Rehash data with the current default algorithm
     */
    public function upgradeHash($data, $oldHash) {
        // Verify the old hash first
        if (!$this->verify($data, $oldHash)) {
            throw new RuntimeException("Cannot upgrade an invalid hash");
        }
        
        // Get algorithm ID from old hash
        $oldAlgoId = ord(hex2bin($oldHash)[0]);
        $newAlgoId = self::$supportedAlgorithms[$this->defaultAlgorithm]['id'];
        
        // Only upgrade if the new algorithm has a higher ID (assumed to be stronger)
        if ($newAlgoId <= $oldAlgoId) {
            return $oldHash; // No upgrade needed
        }
        
        // Create new hash with current default algorithm
        return $this->hash($data);
    }
}

// Example usage
$hashManager = new AgileHashManager('SHA224'); // Start with SHA-224

// Store a hash in the database
$userData = "user_password_123";
$storedHash = $hashManager->hash($userData);
echo "Original hash (SHA-224): {$storedHash}\n";

// Later, verify the hash
$isValid = $hashManager->verify($userData, $storedHash);
echo "Verification result: " . ($isValid ? "Valid" : "Invalid") . "\n";

// Years later, migrate to a stronger algorithm
$hashManager->setDefaultAlgorithm('SHA384');

// When user logs in, upgrade their hash
$upgradedHash = $hashManager->upgradeHash($userData, $storedHash);
echo "Upgraded hash (SHA-384): {$upgradedHash}\n";

// Future verification works with the upgraded hash
$isStillValid = $hashManager->verify($userData, $upgradedHash);
echo "Verification with upgraded hash: " . ($isStillValid ? "Valid" : "Invalid") . "\n";
?>

SHA-224 IMPLEMENTATION SECURITY AUDIT CHECKLIST

1. IMPLEMENTATION CORRECTNESS
   [ ] Produces correct outputs for NIST test vectors
   [ ] Handles variable-length inputs correctly
   [ ] Processes edge cases properly (empty string, large inputs)
   [ ] Correctly manages endianness and byte ordering
   [ ] Handles different input types (strings, byte arrays, streams)

2. USAGE CORRECTNESS
   [ ] HMAC-SHA224 used for message authentication (not raw SHA-224)
   [ ] Specialized functions used for password storage (not raw SHA-224)
   [ ] Constant-time comparison for hash verification
   [ ] Protection against length extension attacks
   [ ] Proper domain separation when using hash for multiple purposes

3. SECURITY CONTROLS
   [ ] Memory containing sensitive data is properly cleared after use
   [ ] Timing side-channels are mitigated
   [ ] Input validation prevents buffer overflows
   [ ] Error handling doesn't leak sensitive information
   [ ] Proper random number generation for salts and nonces

4. API SECURITY
   [ ] Intuitive API that guides developers toward secure usage
   [ ] Clear documentation highlighting security considerations
   [ ] Type safety to prevent misuse
   [ ] Proper encapsulation of implementation details
   [ ] Consistent return types and error handling

5. IMPLEMENTATION SOURCES
   [ ] Known, trusted library used (not custom implementation)
   [ ] Library correctly installed and configured
   [ ] Library is up-to-date with security patches
   [ ] No modifications made to standard implementation
   [ ] Implementation source is validated (checksums, signatures)

6. TESTING COVERAGE
   [ ] Unit tests verify correct operation
   [ ] Fuzz testing has been performed
   [ ] Performance testing under different loads
   [ ] Side-channel testing has been conducted
   [ ] Integration testing in actual usage scenarios

7. DOCUMENTATION
   [ ] Security-relevant behaviors are documented
   [ ] Limitations and constraints are clearly stated
   [ ] Secure usage patterns are provided in examples
   [ ] Version and algorithm details are tracked
   [ ] Dependencies and their security status are documented