Part1 - End-to-End data Encryption Using Public and Private Keys in java / Spring Boot 🌱

• In today's digital age, securing sensitive information during data transmission over a network is paramount. Whether it's private messages, financial transactions, or any other form of data exchange, safeguarding data from prying eyes is crucial.

• End-to-end encryption is a powerful technique that ensures data remains confidential during its journey across the network. 

• In this guide, we will explore the concept of end-to-end encryption using public and private keys and demonstrate how to implement it in a Spring Boot application.

Understanding End-to-End Encryption 🛡️

• End-to-end encryption is a cryptographic method that ensures data remains encrypted from the sender's end until it reaches the intended recipient. This means that even if a malicious entity intercepts the data during its transit, they cannot decipher it without the appropriate decryption key. To achieve this, we utilize a pair of keys: a public key and a private key.

• Public Key 🔑: 
• This key is available to anyone who wants to send encrypted data to the recipient. It is used for encryption and can only decrypt data that the recipient's private key can decrypt. It's called the "public" key because it's not kept secret.
• Private Key 🤐: 
• This key is kept securely by the recipient and is used for decrypting data that has been encrypted with their public key. It must never be shared with anyone.

Data Transmission Over a Network 🌐

• When data is transmitted over a network, it typically involves multiple hops and can traverse various intermediary devices, such as routers and switches. During this process, data packets may be vulnerable to interception by unauthorized parties. To ensure the security of data transmission, end-to-end encryption becomes crucial.

• End-to-end encryption ensures that data remains encrypted not only during its transmission over the network but also at rest on intermediary servers or devices. Only the recipient with the private key can decrypt and access the original data.

Setting up a Spring Boot Project 🌱

• Before we dive into the code, let's set up a Spring Boot project. You can use Spring Initializr or your preferred IDE to create a new Spring Boot application. Make sure to include the necessary dependencies, such as Spring Web, in your project.

Step1: Generating Public and Private Keys 🔐

• In a real-world scenario, the keys would be generated and managed securely. For simplicity, we will generate keys on the fly. In a production environment, you should use a trusted key management system.

import java.security.*;

public class KeyPairGeneratorExample {
    public static void main(String[] args) throws NoSuchAlgorithmException {
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        keyPairGenerator.initialize(2048); // Key size
        KeyPair keyPair = keyPairGenerator.generateKeyPair();
        
        PublicKey publicKey = keyPair.getPublic();
        PrivateKey privateKey = keyPair.getPrivate();
    }
}

Step2: Sender's Code ✉️

• Now, let's write the code for the sender. In this example, we will encrypt a message using the recipient's public key.

import java.security.*;
import javax.crypto.*;
import java.util.Base64;

public class Sender {
    public static void main(String[] args) throws Exception {
        // Load recipient's public key
        byte[] publicKeyBytes = /* Load recipient's public key bytes */;
        PublicKey publicKey = KeyFactory.getInstance("RSA")
            .generatePublic(new X509EncodedKeySpec(publicKeyBytes));

        // Create a cipher
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);

        // Encrypt the message
        byte[] messageBytes = "This is a secret message.".getBytes();
        byte[] encryptedBytes = cipher.doFinal(messageBytes);

        // Send the encrypted message to the recipient
        String encryptedMessage = Base64.getEncoder().encodeToString(encryptedBytes);
        System.out.println("Encrypted Message: " + encryptedMessage);
    }
}

Explaining the Sender's Code 📨

• Loading Recipient's Public Key: Before sending the message, the sender needs the recipient's public key. In practice, this key should be securely obtained from the recipient.

• Creating a Cipher: A Cipher object is created using the "RSA/ECB/PKCS1Padding" transformation, which is a commonly used encryption algorithm.

• Initializing the Cipher: The cipher is initialized for encryption using the recipient's public key.

• Encrypting the Message: The sender's message is encrypted using the doFinal method, which produces the ciphertext.

• Encoding for Transmission: The encrypted bytes are Base64-encoded to ensure safe transmission and printed as the "Encrypted Message."

Step3: Receiver's Code 📬

• On the receiver's end, we will use the private key to decrypt the message.

import java.security.*;
import javax.crypto.*;
import java.util.Base64;
public class Receiver {
    public static void main(String[] args) throws Exception {
        // Load recipient's private key
        byte[] privateKeyBytes = /* Load recipient's private key bytes */;
        PrivateKey privateKey = KeyFactory.getInstance("RSA")
            .generatePrivate(new PKCS8EncodedKeySpec(privateKeyBytes));
        // Create a cipher
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        // Retrieve the encrypted message
        String encryptedMessage = /* Receive the encrypted message */;
        byte[] encryptedBytes = Base64.getDecoder().decode(encryptedMessage);
        // Decrypt the message
        byte[] decryptedBytes = cipher.doFinal(encryptedBytes);
        String decryptedMessage = new String(decryptedBytes);
        System.out.println("Decrypted Message: " + decryptedMessage);
    }
}

Explaining the Receiver's Code 📪

• Loading Recipient's Private Key: Similarly, the recipient needs their private key to decrypt the message. This key must be securely stored and managed.

• Creating a Cipher: A Cipher object is created with the same encryption transformation used by the sender.

• Initializing the Cipher: The cipher is initialized for decryption using the recipient's private key.

• Retrieving the Encrypted Message: The receiver receives the Base64-encoded encrypted message.

• Decrypting the Message: The doFinal method is used to decrypt the message, resulting in the original plaintext.

Conclusion 🌟

• End-to-end encryption using public and private keys is a robust method for securing data during its transmission over a network. 

• In this guide, we've covered the fundamental concepts, explained the importance of data transmission security, and provided step-by-step code for both the sender and receiver sides of a Spring Boot application. 

• It's important to note that in a production environment, key management and security practices should be rigorously followed to ensure the confidentiality and integrity of data. 🚀🔒