Creating Your Own Custom Encryption Using PHP

Encryption has been a crucial part of securing data in today’s digital world. From securing communication to protecting sensitive information, encryption serves as the bedrock of privacy and security. In this article, we explore how PHP can be used to create a custom encryption mechanism that employs the XOR (exclusive OR) operation for data encryption and decryption. By diving deep into the code, we’ll understand the inner workings of how this encryption process works and its potential applications.

What is Encryption?

Before we dive into the specific implementation of encryption, it’s important to have a clear understanding of what encryption is. Encryption is the process of converting data from a readable format (plaintext) into an unreadable format (ciphertext) to prevent unauthorized access. The transformation is done using an algorithm and a key. The encrypted data can only be decrypted (converted back into plaintext) with the correct key.

Encryption is used in a variety of contexts, from securing communication between two parties over the internet to storing passwords in a secure way. Common encryption methods include symmetric encryption, where the same key is used for both encryption and decryption, and asymmetric encryption, which uses a pair of keys—one public and one private.

In this article, we’ll focus on a custom, simplified approach using XOR encryption, which is often used in lightweight encryption systems, such as those found in basic file protection or simple communication systems.

Understanding XOR Encryption

The XOR operation is a bitwise operation that takes two bits and returns 1 if the bits are different and 0 if they are the same. This simple mathematical operation can be used to encrypt and decrypt data by applying it to each character of the data with a key.

When applied repeatedly to a set of data using a key, XOR encryption works by flipping the bits of the data according to the key. The beauty of XOR encryption is that it is symmetric, meaning that the same operation can be used for both encryption and decryption. For example, if a character is encrypted by XORing it with a key, the same character can be decrypted by XORing it again with the same key.

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The CustomEncryptor Class

In the code provided, we see a class named CustomEncryptor. This class handles the encryption and decryption process, with the XOR operation being the core of its mechanism. Let’s break down the functionality of the class step by step.

The Constructor

The class starts with a constructor method __construct($key). This method accepts a key parameter, which will be used in the XOR encryption and decryption operations. The key is stored as a private class variable $key and is used throughout the class.

public function __construct($key) {
    $this->key = $key; // Directly using the provided key
}

By passing the key to the constructor, the CustomEncryptor object is initialized with the key that will be used to both encrypt and decrypt the data.

The Encrypt Method

Next, the class provides an encrypt($plaintext) method, which encrypts a given plaintext string. The method first passes the plaintext to the private xorEncrypt() method, which performs the XOR encryption. The resulting ciphertext is then encoded into a base64 string.

public function encrypt($plaintext) {
    $ciphertext = $this->xorEncrypt($plaintext, $this->key);
    return base64_encode($ciphertext);
}

Base64 encoding is used here to ensure that the ciphertext can be represented as a string and transmitted without any issues. Base64 encoding converts binary data into a string format that is safe for text-based protocols, such as HTTP or email.

The Decrypt Method

The decrypt($ciphertext) method is responsible for reversing the encryption process. It first decodes the base64-encoded ciphertext back into its original binary form and then applies the XOR decryption operation using the same key that was used for encryption.

public function decrypt($ciphertext) {
    $ciphertext = base64_decode($ciphertext);
    return $this->xorEncrypt($ciphertext, $this->key);
}

Because XOR encryption is symmetric, the same method xorEncrypt() is used for both encryption and decryption. When the XOR operation is applied again to the encrypted data with the same key, it “cancels out” the original encryption and returns the original plaintext.

The XOR Encryption Method

The core of the encryption and decryption process lies in the xorEncrypt($data, $key) method. This method iterates over each character of the data and applies the XOR operation with the corresponding character in the key. If the key is shorter than the data, it wraps around and repeats the key.

private function xorEncrypt($data, $key) {
    $output = '';
    for ($i = 0, $keyLen = strlen($key); $i < strlen($data); $i++) {
        $output .= $data[$i] ^ $key[$i % $keyLen]; // Simple XOR encryption
    }
    return $output;
}

The XOR operation is applied to each byte of the data, producing the ciphertext. The % operator ensures that if the key is shorter than the data, it will repeat itself cyclically.

Example Usage

The code also includes an example of how to use the CustomEncryptor class. It shows how to instantiate the class with a private key, encrypt a plaintext string, and then decrypt the ciphertext to recover the original message.

$privateKey = "MySecretKey123";
$encryptor = new CustomEncryptor($privateKey);

$originalText = "Hello, this is a secret message!";
$encryptedText = $encryptor->encrypt($originalText);
$decryptedText = $encryptor->decrypt($encryptedText);

echo "Original: $originalText\n";
echo "Encrypted: $encryptedText\n";
echo "Decrypted: $decryptedText\n";

In this example, the original plaintext message “Hello, this is a secret message!” is encrypted and then decrypted back into its original form. The output shows the plaintext, encrypted ciphertext, and decrypted text.

Full Source Code : Custom Encryption using PHP

<?php

class CustomEncryptor {
    private $key;

    public function __construct($key) {
        $this->key = $key; // Directly using the provided key
    }

    public function encrypt($plaintext) {
        $ciphertext = $this->xorEncrypt($plaintext, $this->key);
        return base64_encode($ciphertext);
    }

    public function decrypt($ciphertext) {
        $ciphertext = base64_decode($ciphertext);
        return $this->xorEncrypt($ciphertext, $this->key);
    }

    private function xorEncrypt($data, $key) {
        $output = '';
        for ($i = 0, $keyLen = strlen($key); $i < strlen($data); $i++) {
            $output .= $data[$i] ^ $key[$i % $keyLen]; // Simple XOR encryption
        }
        return $output;
    }
}

// Example Usage
$privateKey = "MySecretKey123";
$encryptor = new CustomEncryptor($privateKey);

$originalText = "Hello, this is a secret message!";
$encryptedText = $encryptor->encrypt($originalText);
$decryptedText = $encryptor->decrypt($encryptedText);

echo "Original: $originalText\n";
echo "Encrypted: $encryptedText\n";
echo "Decrypted: $decryptedText\n";

?>

Use Cases and Applications

While XOR encryption is not recommended for securing sensitive data in production environments, it has some interesting use cases, especially in educational settings or for light encryption needs.

1. Educational Purpose: XOR encryption is a great tool for teaching the basics of cryptography. It provides a simple and intuitive introduction to the concept of encryption and how bitwise operations can be used to transform data.

2. Obfuscation: XOR encryption can be used for simple obfuscation of data. While it is not secure for serious use, it can be used to obscure information in a non-critical context, such as hiding configuration values or license keys in an application.

3. Lightweight Encryption: For situations where security is not a primary concern (e.g., protecting data in a local environment or within a controlled system), XOR encryption can provide lightweight, fast encryption without the overhead of more complex algorithms.

4. Challenge in Cryptography: XOR encryption, with its simplicity, often serves as a challenge for cryptography enthusiasts. Many exercises and challenges involve breaking XOR encryption to illustrate the importance of more robust encryption schemes in real-world applications.

While XOR encryption is far from the most secure encryption method available, it provides a simple and effective introduction to the concepts of cryptography. In this article, we explored a custom PHP implementation that leverages XOR encryption for both encrypting and decrypting data. Although not suitable for high-security applications, XOR encryption can be a valuable tool for learning, experimentation, and lightweight encryption in specific use cases.

In the modern world of cryptography, where advanced algorithms such as AES (Advanced Encryption Standard) dominate, XOR encryption serves as a reminder of how even the most basic operations can have a profound impact on data security. Whether used in educational contexts or as a light obfuscation technique, XOR encryption has its place in the world of software development and cryptographic research.