Added Lab2/Lab3 IS

IS/Lab/Lab2/multiround_aes_192

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+from Crypto.Cipher import AES
+from Crypto.Util.Padding import pad, unpad
+
+def aes_cipher(key):
+    return AES.new(key.encode('utf-8'), AES.MODE_ECB)
+
+def aes_en(ptext, key):
+    cipher = aes_cipher(key)
+    ptext = pad(ptext.encode('utf-8'), AES.block_size)
+    return cipher.encrypt(ptext)
+
+def aes_de(ctext, key):
+    cipher = aes_cipher(key)
+    decrypted = cipher.decrypt(ctext)
+    return unpad(decrypted, AES.block_size).decode('utf-8')
+
+def aespad_key(key):
+        return key.ljust(24)[:24]
+
+def aes_en_trace(ptext, key):
+    key = aespad_key(key)
+    key_bytes = key.encode('utf-8')
+    cipher = AES.new(key_bytes, AES.MODE_ECB)
+    blocks = pad(ptext.encode('utf-8'), AES.block_size)
+
+    print("AES-192 (ECB) concise steps:")
+    print("  • Key expansion: Nk=6, Nb=4, Nr=12 → 13 round keys")
+    print("  • Initial round: AddRoundKey")
+    print("  • Main rounds (1..11): SubBytes → ShiftRows → MixColumns → AddRoundKey")
+    print("  • Final round (12): SubBytes → ShiftRows → AddRoundKey\n")
+
+    out = bytearray()
+    for i in range(0, len(blocks), 16):
+        block = blocks[i:i+16]
+        print(f"Block {i//16} plaintext: {block.hex()}")
+        print("  Round 0: AddRoundKey")
+        for r in range(1, 12):
+            print(f"  Round {r}: SubBytes → ShiftRows → MixColumns → AddRoundKey")
+        print("  Round 12: SubBytes → ShiftRows → AddRoundKey")
+        cblock = cipher.encrypt(block)
+        print(f"  Ciphertext block: {cblock.hex()}\n")
+        out.extend(cblock)
+    return bytes(out)
+
+def main():
+    default_pt = "MIT AES DEMO"        
+    default_key = "MIT-AES-192-DEMO-KEY-24!"  
+
+    ptext = input(f"Enter plaintext (blank={default_pt}): ").strip()
+    key = input(f"Enter key (blank={default_key}): ").strip()
+    if not ptext:
+        ptext = default_pt
+    if not key:
+        key = default_key
+
+    ctext = aes_en_trace(ptext, key)
+    print("Ciphertext:", ctext.hex())
+    print("Decrypted:", aes_de(ctext, aespad_key(key)))
+
+if __name__ == '__main__':
+    main()

IS/Lab/Lab3/DiffieHellman.py

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+import time
+from dataclasses import dataclass
+
+from Crypto.Hash import SHA256
+from Crypto.Protocol.KDF import HKDF
+from Crypto.Util import number
+
+
+def rfc3526_group14() -> tuple[int, int]:
+    """
+    Return the 2048-bit MODP Group (Group 14) parameters from RFC 3526.
+
+    g = 2
+    p is the safe prime specified in RFC 3526, section 3.
+    """
+    # RFC 3526 Group 14 (2048-bit MODP) prime (hex, concatenated)
+    p_hex = (
+        "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1"
+        "29024E088A67CC74020BBEA63B139B22514A08798E3404DD"
+        "EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245"
+        "E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED"
+        "EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3D"
+        "C2007CB8A163BF0598DA48361C55D39A69163FA8FD24CF5F"
+        "83655D23DCA3AD961C62F356208552BB9ED529077096966D"
+        "670C354E4ABC9804F1746C08CA18217C32905E462E36CE3B"
+        "E39E772C180E86039B2783A2EC07A28FB5C55DF06F4C52C9"
+        "DE2BCBF6955817183995497CEA956AE515D2261898FA0510"
+        "15728E5A8AACAA68FFFFFFFFFFFFFFFF"
+    )
+    p = int(p_hex, 16)
+    g = 2
+    return p, g
+
+
+def int_to_fixed_length_bytes(value: int, length_bits: int) -> bytes:
+    length_bytes = (length_bits + 7) // 8
+    return value.to_bytes(length_bytes, byteorder="big")
+
+
+def generate_keypair(p: int, g: int, private_bits: int = 256) -> tuple[int, int]:
+    """
+    Generate a Diffie-Hellman private/public key pair.
+
+    - private_bits controls the size of the secret exponent for performance and security.
+      256 bits is a common choice for Group 14.
+    """
+    a = 0
+    while a < 2:
+        a = number.getRandomNBitInteger(private_bits)
+    A = pow(g, a, p)
+    return a, A
+
+
+def derive_shared_key(peer_public: int, private: int, p: int, key_len: int = 32) -> bytes:
+    """
+    Compute the shared secret and derive a symmetric key using HKDF-SHA256.
+    Returns key_len bytes (default 32 bytes = 256-bit key).
+    """
+    shared_secret = pow(peer_public, private, p)
+    # Use fixed-length big-endian encoding of the shared secret for KDF input
+    shared_bytes = int_to_fixed_length_bytes(shared_secret, p.bit_length())
+    key = HKDF(shared_bytes, key_len, salt=None, hashmod=SHA256, context=b"DH key")
+    return key
+
+
+@dataclass
+class TimingResult:
+    alice_keygen_s: float
+    bob_keygen_s: float
+    alice_exchange_s: float
+    bob_exchange_s: float
+
+
+def measure_timings(p: int, g: int, private_bits: int = 256) -> TimingResult:
+    start = time.perf_counter()
+    a_priv, a_pub = generate_keypair(p, g, private_bits)
+    alice_keygen_s = time.perf_counter() - start
+
+    start = time.perf_counter()
+    b_priv, b_pub = generate_keypair(p, g, private_bits)
+    bob_keygen_s = time.perf_counter() - start
+
+    # Exchange
+    start = time.perf_counter()
+    a_key = derive_shared_key(b_pub, a_priv, p)
+    alice_exchange_s = time.perf_counter() - start
+
+    start = time.perf_counter()
+    b_key = derive_shared_key(a_pub, b_priv, p)
+    bob_exchange_s = time.perf_counter() - start
+
+    # Sanity check
+    if a_key != b_key:
+        raise RuntimeError("Derived keys do not match. Check parameters.")
+
+    return TimingResult(
+        alice_keygen_s=alice_keygen_s,
+        bob_keygen_s=bob_keygen_s,
+        alice_exchange_s=alice_exchange_s,
+        bob_exchange_s=bob_exchange_s,
+    )
+
+
+def main():
+    p, g = rfc3526_group14()
+
+    timings = measure_timings(p, g, private_bits=256)
+
+    print("Diffie-Hellman (RFC3526 Group 14, g=2)")
+    print(f"Prime bits: {p.bit_length()}\n")
+
+    print("Timings (seconds):")
+    print(f"- Alice key generation: {timings.alice_keygen_s:.6f}")
+    print(f"- Bob   key generation: {timings.bob_keygen_s:.6f}")
+    print(f"- Alice key exchange:   {timings.alice_exchange_s:.6f}")
+    print(f"- Bob   key exchange:   {timings.bob_exchange_s:.6f}")
+
+
+if __name__ == "__main__":
+    main()
+
+

IS/Lab/Lab3/ECC.py

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+from Crypto.PublicKey import ECC
+from Crypto.Cipher import AES
+from Crypto.Hash import SHA256
+import binascii
+
+
+def ecc_keygen(curve: str = 'P-256') -> ECC.EccKey:
+    return ECC.generate(curve=curve)
+
+
+def ecc_encrypt(plaintext: str, recipient_public_key: ECC.EccKey):
+    eph_private = ECC.generate(curve=recipient_public_key.curve)
+    shared_point = recipient_public_key.pointQ * eph_private.d
+    shared_x = int(shared_point.x)
+    aes_key = SHA256.new(shared_x.to_bytes(32, 'big')).digest()
+
+    cipher = AES.new(aes_key, AES.MODE_GCM)
+    ciphertext, tag = cipher.encrypt_and_digest(plaintext.encode('utf-8'))
+
+    return {
+        'ephemeral_pub_der': eph_private.public_key().export_key(format='DER'),
+        'nonce': cipher.nonce,
+        'tag': tag,
+        'ciphertext': ciphertext,
+    }
+
+
+def ecc_decrypt(enc: dict, recipient_private_key: ECC.EccKey) -> str:
+    eph_public = ECC.import_key(enc['ephemeral_pub_der'])
+    shared_point = eph_public.pointQ * recipient_private_key.d
+    shared_x = int(shared_point.x)
+    aes_key = SHA256.new(shared_x.to_bytes(32, 'big')).digest()
+
+    cipher = AES.new(aes_key, AES.MODE_GCM, nonce=enc['nonce'])
+    plaintext = cipher.decrypt_and_verify(enc['ciphertext'], enc['tag'])
+    return plaintext.decode('utf-8')
+
+
+def main():
+    print('Welcome to ECC (ECIES-style)')
+    ptext = input('Enter plaintext: ')
+
+    priv_key = ecc_keygen()
+    pub_key = priv_key.public_key()
+
+    print('\nPublic Key (Qx, Qy):')
+    print('Qx =', hex(int(pub_key.pointQ.x)))
+    print('Qy =', hex(int(pub_key.pointQ.y)))
+
+    enc = ecc_encrypt(ptext, pub_key)
+    print("\nYour ciphertext (hex):", binascii.hexlify(enc['ciphertext']).decode())
+
+    decrypted = ecc_decrypt(enc, priv_key)
+    print('Your decrypted plaintext:', decrypted)
+
+
+if __name__ == '__main__':
+    main()

IS/Lab/Lab3/ElGamal.py

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+import random
+from Crypto.Util.number import getPrime
+
+def elgamal_keygen(bits=512):
+    p = getPrime(bits)
+    g = random.randint(2, p-1)
+    x = random.randint(1, p-2)  # private key
+    h = pow(g, x, p)  # public key component
+    return (p, g, h), x
+
+def elgamal_encrypt(message, pub_key):
+    p, g, h = pub_key
+    m = int.from_bytes(message.encode('utf-8'), 'big')
+    if m >= p:
+        raise ValueError("Message too large for key size")
+    
+    k = random.randint(1, p-2)
+    c1 = pow(g, k, p)
+    c2 = (m * pow(h, k, p)) % p
+    return (c1, c2)
+
+def elgamal_decrypt(ciphertext, priv_key, pub_key):
+    c1, c2 = ciphertext
+    p, g, h = pub_key
+    x = priv_key
+    
+    s = pow(c1, x, p)
+    s_inv = pow(s, p-2, p)  # modular inverse
+    m = (c2 * s_inv) % p
+    
+    return m.to_bytes((m.bit_length() + 7) // 8, 'big').decode('utf-8')
+
+def main():
+    print("Welcome to ElGamal")
+    ptext = input("Enter plaintext: ")
+    
+    # Generate keys
+    pub_key, priv_key = elgamal_keygen()
+    p, g, h = pub_key
+    
+    print(f"\nPublic Key (p, g, h):")
+    print(f"p = {hex(p)}")
+    print(f"g = {g}")
+    print(f"h = {hex(h)}")
+    
+    # Encrypt
+    ctext = elgamal_encrypt(ptext, pub_key)
+    print(f"\nCiphertext (c1, c2):")
+    print(f"c1 = {hex(ctext[0])}")
+    print(f"c2 = {hex(ctext[1])}")
+    
+    # Decrypt
+    decrypted = elgamal_decrypt(ctext, priv_key, pub_key)
+    print(f"Decrypted: {decrypted}")
+
+if __name__ == '__main__':
+    main()

IS/Lab/Lab3/FileTransfer.py

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+import os
+import time
+import binascii
+from Crypto.PublicKey import RSA, ECC
+from Crypto.Cipher import PKCS1_OAEP, AES
+from Crypto.Hash import SHA256
+from Crypto.Util.Padding import pad, unpad
+from Crypto.Random import get_random_bytes
+from bokeh.plotting import figure, show, output_file
+from bokeh.layouts import gridplot
+from bokeh.models import HoverTool
+
+
+def generate_test_file(size_mb):
+    """Generate test file of specified size in MB"""
+    filename = f"test_file_{size_mb}MB.txt"
+    with open(filename, 'wb') as f:
+        # Write random data
+        for _ in range(size_mb * 1024):  # 1MB = 1024KB
+            f.write(get_random_bytes(1024))
+    return filename
+
+
+def rsa_keygen_timed():
+    """Generate RSA key pair and measure time"""
+    start = time.time()
+    key = RSA.generate(2048)
+    gen_time = time.time() - start
+    return key, gen_time
+
+
+def ecc_keygen_timed():
+    """Generate ECC key pair and measure time"""
+    start = time.time()
+    key = ECC.generate(curve='secp256r1')
+    gen_time = time.time() - start
+    return key, gen_time
+
+
+def rsa_encrypt_file(filename, pub_key):
+    """Encrypt file using RSA with AES hybrid encryption"""
+    start = time.time()
+    
+    # Generate AES key
+    aes_key = get_random_bytes(32)  # 256-bit AES key
+    
+    # Encrypt AES key with RSA
+    rsa_cipher = PKCS1_OAEP.new(pub_key)
+    encrypted_aes_key = rsa_cipher.encrypt(aes_key)
+    
+    # Encrypt file with AES
+    aes_cipher = AES.new(aes_key, AES.MODE_CBC)
+    iv = aes_cipher.iv
+    
+    with open(filename, 'rb') as f:
+        plaintext = f.read()
+    
+    padded_plaintext = pad(plaintext, AES.block_size)
+    ciphertext = aes_cipher.encrypt(padded_plaintext)
+    
+    enc_time = time.time() - start
+    
+    encrypted_data = {
+        'encrypted_aes_key': encrypted_aes_key,
+        'iv': iv,
+        'ciphertext': ciphertext
+    }
+    
+    return encrypted_data, enc_time
+
+
+def rsa_decrypt_file(encrypted_data, priv_key):
+    """Decrypt file using RSA with AES hybrid decryption"""
+    start = time.time()
+    
+    # Decrypt AES key with RSA
+    rsa_cipher = PKCS1_OAEP.new(priv_key)
+    aes_key = rsa_cipher.decrypt(encrypted_data['encrypted_aes_key'])
+    
+    # Decrypt file with AES
+    aes_cipher = AES.new(aes_key, AES.MODE_CBC, encrypted_data['iv'])
+    padded_plaintext = aes_cipher.decrypt(encrypted_data['ciphertext'])
+    plaintext = unpad(padded_plaintext, AES.block_size)
+    
+    dec_time = time.time() - start
+    return plaintext, dec_time
+
+
+def ecc_encrypt_file(filename, pub_key):
+    """Encrypt file using ECC with AES hybrid encryption"""
+    start = time.time()
+    
+    # Generate ephemeral key pair
+    eph_private = ECC.generate(curve='secp256r1')
+    
+    # Compute shared secret
+    shared_point = pub_key.pointQ * eph_private.d
+    shared_x = int(shared_point.x)
+    aes_key = SHA256.new(shared_x.to_bytes(32, 'big')).digest()
+    
+    # Encrypt file with AES
+    aes_cipher = AES.new(aes_key, AES.MODE_GCM)
+    
+    with open(filename, 'rb') as f:
+        plaintext = f.read()
+    
+    ciphertext, tag = aes_cipher.encrypt_and_digest(plaintext)
+    
+    enc_time = time.time() - start
+    
+    encrypted_data = {
+        'ephemeral_pub_der': eph_private.public_key().export_key(format='DER'),
+        'nonce': aes_cipher.nonce,
+        'tag': tag,
+        'ciphertext': ciphertext
+    }
+    
+    return encrypted_data, enc_time
+
+
+def ecc_decrypt_file(encrypted_data, priv_key):
+    """Decrypt file using ECC with AES hybrid decryption"""
+    start = time.time()
+    
+    # Import ephemeral public key
+    eph_public = ECC.import_key(encrypted_data['ephemeral_pub_der'])
+    
+    # Compute shared secret
+    shared_point = eph_public.pointQ * priv_key.d
+    shared_x = int(shared_point.x)
+    aes_key = SHA256.new(shared_x.to_bytes(32, 'big')).digest()
+    
+    # Decrypt file with AES
+    aes_cipher = AES.new(aes_key, AES.MODE_GCM, nonce=encrypted_data['nonce'])
+    plaintext = aes_cipher.decrypt_and_verify(encrypted_data['ciphertext'], encrypted_data['tag'])
+    
+    dec_time = time.time() - start
+    return plaintext, dec_time
+
+
+def measure_performance(file_sizes):
+    """Measure performance for both RSA and ECC"""
+    results = {
+        'file_sizes': file_sizes,
+        'rsa_keygen': [],
+        'ecc_keygen': [],
+        'rsa_encrypt': [],
+        'rsa_decrypt': [],
+        'ecc_encrypt': [],
+        'ecc_decrypt': [],
+        'rsa_key_size': 0,
+        'ecc_key_size': 0
+    }
+    
+    print("Performance Testing - RSA vs ECC File Transfer")
+    print("=" * 50)
+    
+    # Generate keys once
+    rsa_key, rsa_keygen_time = rsa_keygen_timed()
+    ecc_key, ecc_keygen_time = ecc_keygen_timed()
+    
+    # Calculate key sizes
+    results['rsa_key_size'] = len(rsa_key.export_key('DER'))
+    results['ecc_key_size'] = len(ecc_key.export_key(format='DER'))
+    
+    print(f"RSA Key Generation Time: {rsa_keygen_time:.4f} seconds")
+    print(f"ECC Key Generation Time: {ecc_keygen_time:.4f} seconds")
+    print(f"RSA Key Size: {results['rsa_key_size']} bytes")
+    print(f"ECC Key Size: {results['ecc_key_size']} bytes")
+    print()
+    
+    for size in file_sizes:
+        print(f"Testing {size}MB file...")
+        
+        # Generate test file
+        filename = generate_test_file(size)
+        
+        try:
+            # RSA performance
+            rsa_pub = rsa_key.publickey()
+            encrypted_rsa, rsa_enc_time = rsa_encrypt_file(filename, rsa_pub)
+            decrypted_rsa, rsa_dec_time = rsa_decrypt_file(encrypted_rsa, rsa_key)
+            
+            # ECC performance
+            ecc_pub = ecc_key.public_key()
+            encrypted_ecc, ecc_enc_time = ecc_encrypt_file(filename, ecc_pub)
+            decrypted_ecc, ecc_dec_time = ecc_decrypt_file(encrypted_ecc, ecc_key)
+            
+            # Store results
+            results['rsa_keygen'].append(rsa_keygen_time)
+            results['ecc_keygen'].append(ecc_keygen_time)
+            results['rsa_encrypt'].append(rsa_enc_time)
+            results['rsa_decrypt'].append(rsa_dec_time)
+            results['ecc_encrypt'].append(ecc_enc_time)
+            results['ecc_decrypt'].append(ecc_dec_time)
+            
+            print(f"  RSA - Encrypt: {rsa_enc_time:.4f}s, Decrypt: {rsa_dec_time:.4f}s")
+            print(f"  ECC - Encrypt: {ecc_enc_time:.4f}s, Decrypt: {ecc_dec_time:.4f}s")
+            
+        finally:
+            # Clean up test file
+            if os.path.exists(filename):
+                os.remove(filename)
+        
+        print()
+    
+    return results
+
+
+def create_performance_graphs(results):
+    """Create performance comparison graphs using Bokeh"""
+    output_file("file_transfer_performance.html")
+    
+    file_sizes = results['file_sizes']
+    
+    # Encryption time comparison
+    p1 = figure(title="Encryption Time Comparison", x_axis_label="File Size (MB)", 
+                y_axis_label="Time (seconds)", width=400, height=300)
+    p1.line(file_sizes, results['rsa_encrypt'], legend_label="RSA", line_color="red", line_width=2)
+    p1.circle(file_sizes, results['rsa_encrypt'], color="red", size=6)
+    p1.line(file_sizes, results['ecc_encrypt'], legend_label="ECC", line_color="blue", line_width=2)
+    p1.circle(file_sizes, results['ecc_encrypt'], color="blue", size=6)
+    p1.legend.location = "top_left"
+    
+    # Decryption time comparison
+    p2 = figure(title="Decryption Time Comparison", x_axis_label="File Size (MB)", 
+                y_axis_label="Time (seconds)", width=400, height=300)
+    p2.line(file_sizes, results['rsa_decrypt'], legend_label="RSA", line_color="red", line_width=2)
+    p2.circle(file_sizes, results['rsa_decrypt'], color="red", size=6)
+    p2.line(file_sizes, results['ecc_decrypt'], legend_label="ECC", line_color="blue", line_width=2)
+    p2.circle(file_sizes, results['ecc_decrypt'], color="blue", size=6)
+    p2.legend.location = "top_left"
+    
+    # Key generation comparison
+    p3 = figure(title="Key Generation Time", x_axis_label="Algorithm", 
+                y_axis_label="Time (seconds)", width=400, height=300,
+                x_range=["RSA", "ECC"])
+    p3.vbar(x=["RSA", "ECC"], top=[results['rsa_keygen'][0], results['ecc_keygen'][0]], 
+            width=0.5, color=["red", "blue"])
+    
+    # Key size comparison
+    p4 = figure(title="Key Size Comparison", x_axis_label="Algorithm", 
+                y_axis_label="Size (bytes)", width=400, height=300,
+                x_range=["RSA", "ECC"])
+    p4.vbar(x=["RSA", "ECC"], top=[results['rsa_key_size'], results['ecc_key_size']], 
+            width=0.5, color=["red", "blue"])
+    
+    # Create grid layout
+    grid = gridplot([[p1, p2], [p3, p4]])
+    show(grid)
+
+
+def print_security_analysis():
+    """Print security analysis and comparison"""
+    print("\nSecurity Analysis - RSA vs ECC")
+    print("=" * 50)
+    print("RSA (2048-bit):")
+    print("  • Security Level: ~112 bits")
+    print("  • Key Size: Large (2048+ bits)")
+    print("  • Resistance: Integer factorization problem")
+    print("  • Quantum Threat: Vulnerable to Shor's algorithm")
+    print("  • Computational Overhead: High for large keys")
+    print()
+    print("ECC (secp256r1):")
+    print("  • Security Level: ~128 bits")
+    print("  • Key Size: Small (256 bits)")
+    print("  • Resistance: Elliptic curve discrete logarithm problem")
+    print("  • Quantum Threat: Vulnerable to modified Shor's algorithm")
+    print("  • Computational Overhead: Lower than equivalent RSA")
+    print()
+    print("Summary:")
+    print("  • ECC provides equivalent security with smaller keys")
+    print("  • ECC is more efficient for mobile/embedded systems")
+    print("  • RSA is more widely supported and established")
+    print("  • Both require post-quantum alternatives for future security")
+
+
+def main():
+    """Main function to run the file transfer comparison"""
+    file_sizes = [1, 5, 10]  # MB
+    
+    print("Secure File Transfer System - RSA vs ECC Comparison")
+    print("=" * 60)
+    
+    # Measure performance
+    results = measure_performance(file_sizes)
+    
+    # Create performance graphs
+    create_performance_graphs(results)
+    
+    # Print security analysis
+    print_security_analysis()
+    
+    print(f"\nPerformance graphs saved to: file_transfer_performance.html")
+    print("Open the HTML file in your browser to view the interactive graphs.")
+
+
+if __name__ == '__main__':
+    main()

IS/Lab/Lab3/RSA.py

@@ -0,0 +1,39 @@
+from Crypto.PublicKey import RSA
+from Crypto.Cipher import PKCS1_OAEP
+import binascii
+
+def rsa_keygen(bits=2048):
+    key = RSA.generate(bits)
+    return key
+
+def rsa_en(ptext, pub_key):
+    cipher = PKCS1_OAEP.new(pub_key)
+    ctext = cipher.encrypt(ptext.encode('utf-8'))
+    return ctext
+
+def rsa_de(ctext, priv_key):
+    cipher = PKCS1_OAEP.new(priv_key)
+    decrypted = cipher.decrypt(ctext)
+    return decrypted.decode('utf-8')
+
+def main():
+    print("Welcome to RSA")
+    ptext = input("Enter plaintext: ")
+
+    # RSA key pair
+    key = rsa_keygen()
+    pub_key = key.publickey()
+    priv_key = key
+
+    print("\nPublic Key (n, e):")
+    print("n =", hex(pub_key.n))
+    print("e =", pub_key.e)
+
+    ctext = rsa_en(ptext, pub_key)
+    print("\nYour ciphertext (hex):", binascii.hexlify(ctext).decode())
+
+    decrypted = rsa_de(ctext, priv_key)
+    print("Your decrypted plaintext:", decrypted)
+
+if __name__ == '__main__':
+    main()