How to use PHP to develop a simple file encryption and decryption function

How to use PHP to develop a simple file encryption and decryption function

Introduction:
In today's information age, data security has become an important issue. In order to protect the privacy of data, file encryption technology is widely used in various fields. This article will introduce how to use PHP to develop a simple file encryption and decryption function, and provide specific code examples to help readers better understand and practice.

1. Encryption algorithm selection
Before developing the file encryption function, you need to select an appropriate encryption algorithm. Common encryption algorithms include symmetric encryption algorithms and asymmetric encryption algorithms. The symmetric encryption algorithm uses the same key for encryption and decryption and is suitable for encrypting large amounts of data; the asymmetric encryption algorithm uses a pair of keys for encryption and decryption and is suitable for encrypting small amounts of data. This article will choose the AES algorithm based on the symmetric encryption algorithm as an example.

2. Generate a key
Before encryption and decryption, a key needs to be generated. You can use the crypto_create_iv() function provided by PHP to generate a random key.

$key = openssl_random_pseudo_bytes(32); // 生成一个32位的随机密钥

3. File Encryption
The key to file encryption is to encrypt the file content and key and save it to a new file.

function encryptFile($file, $key, $outputFile) {
    $content = file_get_contents($file); // 读取文件内容
    $iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length('aes-256-cbc')); // 生成一个随机初始向量
    $encryptedContent = openssl_encrypt($content, 'aes-256-cbc', $key, 0, $iv); // 对文件内容进行加密

    $fileHandle = fopen($outputFile, 'w'); // 打开一个新的文件用于保存加密后的内容
    fwrite($fileHandle, $iv); // 将初始向量写入文件
    fwrite($fileHandle, $encryptedContent); // 将加密后的内容写入文件
    fclose($fileHandle);
}

4. File decryption
The key to file decryption is to read the encrypted file content and key, decrypt it and save it to a new file.

function decryptFile($file, $key, $outputFile) {
    $fileHandle = fopen($file, 'r'); // 打开被加密的文件
    $iv = fread($fileHandle, openssl_cipher_iv_length('aes-256-cbc')); // 读取初始向量
    $encryptedContent = fread($fileHandle, filesize($file)); // 读取加密后的内容
    fclose($fileHandle);

    $decryptedContent = openssl_decrypt($encryptedContent, 'aes-256-cbc', $key, 0, $iv); // 解密文件内容

    $fileHandle = fopen($outputFile, 'w'); // 打开一个新的文件用于保存解密后的内容
    fwrite($fileHandle, $decryptedContent); // 将解密后的内容写入文件
    fclose($fileHandle);
}

5. Usage Example
The following is a simple usage example that demonstrates how to encrypt a file and decrypt it back.

$file = 'test.txt'; // 要加密的文件
$key = openssl_random_pseudo_bytes(32); // 生成一个32位的随机密钥
$outputFile = 'encrypted.txt'; // 加密后的文件

encryptFile($file, $key, $outputFile);

$decryptedFile = 'decrypted.txt'; // 解密后的文件

decryptFile($outputFile, $key, $decryptedFile);

Conclusion:
Through the introduction of this article, we have learned how to use PHP to develop a simple file encryption and decryption function, and provided specific code examples. Readers can make corresponding improvements and expansions according to their actual needs and security requirements. By using encryption technology, we are able to better protect the security and privacy of files and improve the reliability of data transmission and storage. At the same time, readers also need to pay attention to legal compliance and comply with relevant laws and regulations when using encryption technology.

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