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); // 生成一個(gè)32位的隨機(jī)密鑰

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); // 讀取文件內(nèi)容
    $iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length('aes-256-cbc')); // 生成一個(gè)隨機(jī)初始向量
    $encryptedContent = openssl_encrypt($content, 'aes-256-cbc', $key, 0, $iv); // 對(duì)文件內(nèi)容進(jìn)行加密

    $fileHandle = fopen($outputFile, 'w'); // 打開(kāi)一個(gè)新的文件用于保存加密后的內(nèi)容
    fwrite($fileHandle, $iv); // 將初始向量寫(xiě)入文件
    fwrite($fileHandle, $encryptedContent); // 將加密后的內(nèi)容寫(xiě)入文件
    fclose($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'); // 打開(kāi)被加密的文件
    $iv = fread($fileHandle, openssl_cipher_iv_length('aes-256-cbc')); // 讀取初始向量
    $encryptedContent = fread($fileHandle, filesize($file)); // 讀取加密后的內(nèi)容
    fclose($fileHandle);

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

    $fileHandle = fopen($outputFile, 'w'); // 打開(kāi)一個(gè)新的文件用于保存解密后的內(nèi)容
    fwrite($fileHandle, $decryptedContent); // 將解密后的內(nèi)容寫(xiě)入文件
    fclose($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); // 生成一個(gè)32位的隨機(jī)密鑰
$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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