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Building RSA and AES Encryption in Python: A Step-by-Step Guide for Students

October 20, 2023
Liam Campbell
Liam Campbell
Encryption Algorithm
Liam Campbell is a seasoned Python Coding Specialist with 14 years of practice. He holds a Master's degree from the University of Sydney, Australia.

In the digital age, security is paramount, especially when it comes to transmitting sensitive information over the internet. RSA (Rivest–Shamir–Adleman) and AES (Advanced Encryption Standard) are two widely used encryption algorithms that play a crucial role in securing digital communication. Understanding how to implement these encryption methods in Python is essential for computer science and cybersecurity students. In this step-by-step guide, we'll delve into the world of RSA and AES encryption, providing students with the knowledge and tools needed to write their encryption algorithm assignment using python, mastering these fundamental encryption techniques, and gaining a deeper understanding of encryption's principles. Students can apply this knowledge to enhance the security of data transmission and storage, which is not only relevant for academic purposes but also for addressing real-world challenges in cybersecurity. By implementing RSA and AES encryption in Python, students will be well-equipped to tackle practical tasks and contribute to the ever-evolving field of digital security, all while reinforcing their programming skills.

A Student's Guide to Creating RSA and AES Encryption in Python

  1. Understanding Encryption
  2. Before delving into the intricacies of RSA and AES encryption, it's imperative to establish a firm foundation in the fundamental concept of encryption and comprehend its pivotal role in securing digital communication. Encryption serves as the bedrock of information security, enabling the transformation of easily readable plaintext into an unintelligible ciphertext, rendering it impervious to unauthorized access. This essential technique ensures that in the event of data interception, sensitive information remains shrouded in secrecy, safeguarded by encryption's robust shield, thereby safeguarding the confidentiality and integrity of data transmission across digital networks. Understanding encryption is the initial step towards mastering the intricate art of RSA and AES encryption, forming the cornerstone of knowledge that underpins the realms of cybersecurity and cryptography, protecting information against potential adversaries and prying eyes.

    There are two main types of encryption: symmetric and asymmetric. RSA and AES are examples of asymmetric and symmetric encryption, respectively.

    1. Symmetric Encryption: In symmetric encryption, the same key is used for both encryption and decryption. This key, often referred to as the secret key, is shared by both the sender and the recipient. While symmetric encryption offers speed and efficiency, it poses key distribution challenges, as securely transmitting the secret key to all authorized parties can be complex. Managing the key's confidentiality is crucial in symmetric encryption systems to prevent unauthorized access and maintain the security of the data.
    2. Asymmetric Encryption: Asymmetric encryption introduces the use of two distinct keys—a public key for encryption and a private key for decryption. The public key can be openly shared, allowing anyone to send encrypted messages to the key's owner. However, only the owner, who possesses the private key, can decrypt and access the original data. This approach enhances security, particularly in open network environments where secure key exchange is challenging. Asymmetric encryption methods like RSA provide the foundation for secure digital communication, protecting sensitive data from eavesdroppers and ensuring the authenticity and confidentiality of transmitted information.

  3. RSA Encryption
  4. RSA, an acronym derived from its inventors' last names, Ron Rivest, Adi Shamir, and Leonard Adleman, stands as a prominent asymmetric encryption algorithm. Its widespread usage encompasses securing data transmission and facilitating digital signatures. This encryption technique operates on the principle of two related but distinct keys: a public key for encryption and a private key for decryption. The public key can be openly shared, allowing secure data transmission over open networks, while the private key remains confidential to the intended recipient. RSA's efficiency and robust security make it invaluable in the protection of sensitive information and the establishment of trust in digital communication. Its applications extend to e-commerce, secure email exchanges, and the validation of digital identities through digital signatures, reinforcing its crucial role in the ever-evolving realm of information security.

    Generating Keys

    The RSA encryption process commences with key generation, a fundamental step in the asymmetric encryption scheme. The key generation process is as follows:

    1. Choose two prime numbers, p and q: To create RSA keys, two prime numbers are selected. These prime numbers serve as the building blocks for the keys' security.
    2. Compute their product, n = p * q: The product of these prime numbers, n, is calculated and utilized as the modulus for both the public and private keys. This modulus forms the foundation of RSA's mathematical operations.
    3. Calculate the totient (φ) of n, where φ(n) = (p-1) * (q-1): The totient of n, often denoted as φ(n), is determined. This value is critical in selecting the public and private exponents for the keys.
    4. Choose an integer e such that 1 < e < φ(n) and gcd(e, φ(n)) = 1: An integer e, known as the public key exponent, is selected. It must meet specific criteria, including being greater than 1, less than φ(n), and having no common divisors with φ(n) except 1.
    5. Compute the private key exponent, d, such that (d * e) % φ(n) = 1: The private key exponent, denoted as d, is calculated to satisfy the equation (d * e) % φ(n) = 1. This equation ensures that the private key can accurately decrypt messages encrypted with the public key.


    Once the RSA keys are successfully generated, the encryption process becomes straightforward. To encrypt a message denoted as M, the sender employs the recipient's public key (n, e) and performs the following operation:

    C = Me mod n

    Where C represents the ciphertext. This operation raises the message M to the power of the public key exponent e and then calculates the remainder when divided by the modulus n. The resulting value, C, is the ciphertext, which can be securely transmitted to the recipient.


    Decrypting the ciphertext, C, is a task reserved for the recipient, who utilizes their private key (n, d). The decryption process is as follows:

    M = Cd mod n

    In this operation, the ciphertext C is raised to the power of the private key exponent d, followed by computing the remainder when divided by the modulus n. The outcome of this operation is the original plaintext message, M. This completes the process, and the recipient can now access the original, intelligible content of the encrypted message.

    Understanding the encryption and decryption processes of RSA is fundamental for users who wish to harness the power of asymmetric encryption for secure data transmission and communication. This knowledge empowers individuals to leverage RSA's capabilities for securing sensitive information, digital signatures, and maintaining confidentiality in the digital domain.

  5. AES Encryption
  6. AES, the abbreviation for Advanced Encryption Standard, is a prominent symmetric encryption algorithm. It distinguishes itself through its widespread application in data encryption, both for safeguarding data at rest and securing information during transmission. Unlike RSA, which operates with distinct public and private keys, AES simplifies the encryption process by utilizing the same key for both encryption and decryption. This key, known as the symmetric key, offers speed and efficiency in securing data, making it a preferred choice for various applications such as securing files, protecting sensitive data during transfer, and ensuring data integrity. The understanding of AES encryption is invaluable for individuals and organizations seeking robust, efficient, and high-performance data protection solutions, underpinning the security of digital assets and enhancing trust in data handling and transmission.

    Key Generation

    Before you can begin using AES encryption, the first crucial step is key generation. AES supports a range of key sizes, including 128, 192, or 256 bits. It's essential to note that the security level of the encryption increases with the key length. In the key generation process, a random key of the desired length is selected. This key is the linchpin of the entire encryption process, and its quality and strength play a pivotal role in the security of the data it protects.


    AES encryption operates by dividing the plaintext data into blocks, typically 128 bits or 16 bytes at a time. Each block is then processed using the selected encryption key to generate the corresponding ciphertext. This block-wise encryption technique is a fundamental aspect of AES and contributes to its effectiveness in securing data. As each block is independently encrypted, it ensures that even large amounts of data can be securely protected. Understanding this block-based encryption process is key to effectively implementing AES encryption and ensuring the confidentiality and integrity of your data.

    AES employs a series of transformations including substitution, permutation, and mixing. The data undergoes a sequence of operations that include byte substitution, row shifting, column mixing, and adding round keys. These transformations introduce confusion and diffusion, making it extremely difficult for attackers to reverse the encryption process. The data is XORed with round keys derived from the original encryption key, further enhancing security. This complex process is repeated for multiple rounds, with the number of rounds varying based on the key size (10 rounds for 128-bit keys, 12 rounds for 192-bit keys, and 14 rounds for 256-bit keys). Understanding these transformations is critical for comprehending the inner workings of AES encryption and its formidable data protection capabilities.


    Decryption with AES is essentially the reverse of encryption. The ciphertext is processed with the same encryption key, but in reverse order, applying the inverse transformations to recover the original plaintext. This process effectively "undoes" the encryption and allows the recipient to access the intelligible content of the data. The decryption process involves steps such as removing the round keys, performing the inverse substitution, permutation, and mixing operations, and finally, XORing the data with the original encryption key. Understanding the decryption process is fundamental for utilizing AES encryption and ensuring that secure data transmission and storage can be efficiently and reliably decrypted.

  7. Implementing RSA and AES in Python
  8. In this section, we'll bridge the gap between theory and application by demonstrating how to implement RSA and AES encryption in Python. By providing practical, hands-on guidance, we aim to equip you with the skills and knowledge necessary to apply these encryption techniques in real-world scenarios. To get started, ensure that you have Python installed on your system. As you delve into the coding and implementation, you'll gain a deeper understanding of how these encryption methods work in practice, enabling you to utilize them for securing data, communication, and storage. This practical experience is invaluable for students, programmers, and security professionals looking to fortify their data protection capabilities and contribute to the ever-evolving field of digital security.

Setting Up Your Development Environment

Before diving into the implementation of RSA and AES encryption in Python, it's crucial to establish your development environment. You'll need two key components: the Python programming language and the cryptography library. The cryptography library simplifies working with both RSA and AES encryption, providing essential tools and functions for cryptographic operations. To install this library, you can use the Python package manager, pip. Ensuring you have these tools in place is the first step toward successfully coding and experimenting with encryption techniques in Python. You can install it using pip:

```bash pip install cryptography ```

With the necessary tools in place, we can begin implementing RSA and AES encryption in Python. These hands-on implementations will not only solidify your understanding of encryption but also equip you with practical skills that are invaluable in real-world applications. As you progress through the coding process, you'll gain insights into how these encryption methods work, from key generation to encryption and decryption. This knowledge and practical experience will empower you to secure data effectively and address the ever-evolving challenges in the field of cybersecurity. So, let's get started on the journey of implementing RSA and AES encryption in Python.

Building RSA Encryption

Our first step is to build an RSA encryption example. In this process, we'll create the necessary keys, encrypt a message, and subsequently decrypt it to demonstrate the functionality of the RSA encryption system.

```python from cryptography.hazmat.primitives.asymmetric import rsa from cryptography.hazmat.primitives import serialization from cryptography.hazmat.primitives import hashes from cryptography.hazmat.primitives.asymmetric import padding # Generate RSA keys private_key = rsa.generate_private_key( public_exponent=65537, key_size=2048, ) # Serialize the private key private_pem = private_key.private_bytes( encoding=serialization.Encoding.PEM, format=serialization.PrivateFormat.PKCS8, encryption_algorithm=serialization.NoEncryption() ) # Serialize the public key public_key = private_key.public_key() public_pem = public_key.public_bytes( encoding=serialization.Encoding.PEM, format=serialization.PublicFormat.SubjectPublicKeyInfo ) # Message to encrypt message = b"Hello, RSA Encryption!" # Encrypt the message ciphertext = public_key.encrypt( message, padding.OAEP( mgf=padding.MGF1(algorithm=hashes.SHA256()), algorithm=hashes.SHA256(), label=None ) ) # Decrypt the message plaintext = private_key.decrypt( ciphertext, padding.OAEP( mgf=padding.MGF1(algorithm=hashes.SHA256()), algorithm=hashes.SHA256(), label=None ) ) print("Original Message:", message) print("Decrypted Message:", plaintext.decode()) ```

In this code, we generate RSA keys, which consist of both a public key for encryption and a private key for decryption. The public key can be freely shared and is used for encrypting messages, ensuring their security during transmission. On the other hand, the private key, which must remain confidential, is employed to decrypt the messages and recover the original content. These keys are at the core of RSA's asymmetric encryption, enabling secure communication while maintaining the confidentiality and integrity of the data. By understanding and implementing this process, you'll be better equipped to utilize RSA encryption for a wide range of applications, from secure data transmission to digital signatures and more.

Building AES Encryption

In this phase, we shift our focus to implementing AES encryption. We'll embark on the journey of creating a secure channel for our data by generating a random AES key, encrypting a message, and subsequently decrypting it. AES, as a symmetric encryption algorithm, employs the same key for both encryption and decryption, making the protection of sensitive data a seamless process.

```python from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC from cryptography.hazmat.primitives import hashes from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC from cryptography.hazmat.primitives import serialization from cryptography.hazmat.primitives.asymmetric import padding from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC # Message to encrypt message = b"Hello, AES Encryption!" # Generate a random AES key salt = b'\x9eRcE\x18\xb4\xa1#\x95L\x8f\x0c\xa5`\xb8\x1c' kdf = PBKDF2HMAC( algorithm=hashes.SHA256(), iterations=100000, salt=salt, length=32, ) # Replace 'your_password' with a secure passphrase key = kdf.derive(b'your_password') # Encrypt the message iv = b'\x1a\xde\xd8\xfaQ%\x0e\xd3\x1f\xef\x14\xb7\xb7Kj' cipher = Cipher(algorithms.AES(key), modes.CFB(iv)) encryptor = cipher.encryptor() ciphertext = encryptor.update(message) + encryptor.finalize() # Decrypt the message decryptor = cipher.decryptor() decrypted_message = decryptor.update(ciphertext) + decryptor.finalize() print("Original Message:", message) print("Decrypted Message:", decrypted_message) ```

In this code, we initiate the process by generating a random AES key. This key serves as the linchpin of our encryption process, allowing us to secure our data efficiently. We then employ this key to encrypt our message, safeguarding its contents from unauthorized access and potential threats. Subsequently, we leverage the same key and an initialization vector (IV) to decrypt the message, ensuring its integrity and readability are preserved. By mastering this process, you gain a fundamental skill in implementing AES encryption, an essential tool in securing data both at rest and during transmission.


In this step-by-step guide, we've explored the concepts of RSA and AES encryption and demonstrated how to implement them in Python. Understanding these encryption methods is essential for students and professionals working in cybersecurity and cryptography. The knowledge gained in this guide empowers you to navigate the complex and ever-evolving landscape of digital security confidently. You now possess the skills needed to not only understand encryption principles but also to put them into practice effectively.

With the provided code examples, you can now experiment with RSA and AES encryption, helping you solve assignments and gain a deeper understanding of these fundamental encryption techniques. By engaging with these examples, you'll develop a profound grasp of how encryption algorithms function and how they can be leveraged to safeguard sensitive data from prying eyes. This hands-on experience is invaluable for students and professionals alike as they strive to excel in the dynamic field of cybersecurity.

Encryption is a critical aspect of securing data in the digital world, and learning how to implement it is an important skill for anyone interested in cybersecurity and data protection. The digital age continuously presents new challenges and threats to our information security. However, with a solid foundation in encryption techniques, you can contribute to the development of robust solutions to counter these challenges effectively. Armed with this knowledge, you become a valuable asset in the ongoing battle to safeguard sensitive information.

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