## RSA Encryption:

RSA (Rivest–Shamir–Adleman) is an asymmetric encryption algorithm that utilizes a pair of keys: a public key for encryption, a private key for decryption, and can be a topic where you might need help with Python assignment. Our step-by-step Python implementation of RSA encryption will demystify the process for you.

```
```python
# Step 1: Import necessary libraries
import random
import math
# Step 2: Define functions for RSA key generation
def generate_prime(bits):
while True:
n = random.getrandbits(bits)
if n % 2 != 0 and is_prime(n):
return n
def is_prime(n):
if n <= 1:
return False
for i in range(2, int(math.sqrt(n)) + 1):
if n % i == 0:
return False
return True
def extended_gcd(a, b):
if a == 0:
return b, 0, 1
g, y, x = extended_gcd(b % a, a)
return g, x - (b // a) * y, y
def mod_inverse(a, m):
g, x, y = extended_gcd(a, m)
if g != 1:
raise ValueError("Modular inverse does not exist")
return x % m
# Step 3: Generate RSA keys
def generate_rsa_keys(bits):
p = generate_prime(bits)
q = generate_prime(bits)
n = p * q
phi_n = (p - 1) * (q - 1)
while True:
e = random.randint(2, phi_n)
if math.gcd(e, phi_n) == 1:
break
d = mod_inverse(e, phi_n)
return ((e, n), (d, n))
# Step 4: RSA encryption
def rsa_encrypt(plaintext, public_key):
e, n = public_key
encrypted_msg = [pow(ord(char), e, n) for char in plaintext]
return encrypted_msg
# Step 5: RSA decryption
def rsa_decrypt(encrypted_msg, private_key):
d, n = private_key
decrypted_msg = ''.join([chr(pow(char, d, n)) for char in encrypted_msg])
return decrypted_msg
```
```

## Explanation

- We begin by importing the necessary libraries: `random` for generating random numbers, and `math` for mathematical operations.
- We define functions for RSA key generation, ensuring the secure generation of prime numbers and calculating the modular inverse for encryption and decryption.
- Next, we generate RSA keys to create a public-private key pair.
- With our custom `rsa_encrypt` and `rsa_decrypt` functions, we demonstrate how to encrypt and decrypt messages using the generated RSA keys.

## AES Encryption:

AES (Advanced Encryption Standard) is a symmetric encryption algorithm that employs the same key for both encryption and decryption. As part of our guide, we'll illustrate the AES encryption process using Python and the `PyCryptodome` library:

```
```python
# Step 1: Install the required library (if not already installed)
# pip install pycryptodome
# Step 2: Import necessary libraries
from Crypto.Cipher import AES
from Crypto.Random import get_random_bytes
from Crypto.Util.Padding import pad, unpad
# Step 3: AES encryption
def aes_encrypt(plaintext, key):
key = key[:16] # AES-128 requires a 16-byte key
cipher = AES.new(key, AES.MODE_CBC, get_random_bytes(16))
ciphertext = cipher.encrypt(pad(plaintext.encode(), AES.block_size))
return ciphertext
# Step 4: AES decryption
def aes_decrypt(ciphertext, key):
key = key[:16] # AES-128 requires a 16-byte key
cipher = AES.new(key, AES.MODE_CBC, ciphertext[:16])
plaintext = unpad(cipher.decrypt(ciphertext[16:]), AES.block_size)
return plaintext.decode()
```
```

## Explanation:

- To begin, we ensure the `pycryptodome` library is installed, allowing us to access AES functionality.
- We import the necessary modules from the `Crypto` package, including `AES`, `get_random_bytes`, `pad`, and `unpad`.
- Our `aes_encrypt` function demonstrates how to encrypt plaintext using AES with a specified key, providing a crucial layer of security.
- For decryption, we present the `aes_decrypt` function, which utilizes the same key to decode the ciphertext back to its original form.

## Final Note:

We understand that encryption is a complex subject. While this guide provides you with fundamental insights and Python implementations, secure encryption implementation requires additional considerations beyond the provided code. In real-world scenarios, adopting established cryptographic libraries and best practices is essential.