Encrypt and Decrypt files using PHP

Here is the PHP function for encrypt file.

function encrypt_file($file, $destination, $all_arguments) {
     
	$handle = fopen($file, "rb") or die("sorry, Could not open a file."); 

	$contents = fread($handle, filesize($file));
 
	fclose($handle); 

	$iv = substr(md5("\x1B\x3C\x58".$all_arguments, true), 0, 8);
	$key = substr(md5("\x2D\xFC\xD8".$all_arguments, true) . md5("\x2D\xFC\xD9".$all_arguments, true), 0, 24);
	$opts = array('iv'=>$iv, 'key'=>$key);
	$fp = fopen($destination, 'wb') or die("Sorry, Could not open file for writing.");

	stream_filter_append($fp, 'mcrypt.tripledes', STREAM_FILTER_WRITE, $opts); 

	fwrite($fp, $contents) or die("sorry, Could not write to file."); 

	fclose($fp); 
 
}

• Open the file and returns a file pointer resource.
• Returns the read string.
• Close the opened file pointer.
• Add the Mcrypt stream filter with Triple DES
• Write content in the destination file.
• Close the opened file pointer.

Here is the function for decrypt. The decrypted data can be returned as a string or served for download.

function decrypt_file($file,$passphrase) {
	$iv = substr(md5("\x1B\x3C\x58".$passphrase, true), 0, 8);
	$key = substr(md5("\x2D\xFC\xD8".$passphrase, true) .
	md5("\x2D\xFC\xD9".$passphrase, true), 0, 24);
	$opts = array('iv'=>$iv, 'key'=>$key);
	$fp = fopen($file, 'rb');
	stream_filter_append($fp, 'mdecrypt.tripledes', STREAM_FILTER_READ, $opts);
	return $fp;
}

You can use above function as shown below.

encrypt_file('/path/to/file','./upload','YOUR_SECRATE_FILE');


$pass_decrypted = decrypt_file('/path/to/file','YOUR_SECRATE_FILE');
header('Content-type: application/pdf');
fpassthru($pass_decrypted);

How to encrypt/decrypt files with php (mcrypt)?

The mcrypt extension is deprecated in PHP 7.1.0 and removed in PHP 7.2.0. Instead, it is recommended to use the openssl extension which provides more secure encryption methods.

Here’s an example of how to encrypt and decrypt a file using the openssl extension in PHP:

// Encryption function
function encryptFile($inputFile, $outputFile, $key) {
    $data = file_get_contents($inputFile);
    $ivlen = openssl_cipher_iv_length($cipher="AES-128-CBC");
    $iv = openssl_random_pseudo_bytes($ivlen);
    $ciphertext_raw = openssl_encrypt($data, $cipher, $key, $options=OPENSSL_RAW_DATA, $iv);
    $hmac = hash_hmac('sha256', $ciphertext_raw, $key, $as_binary=true);
    $ciphertext = base64_encode( $iv.$hmac.$ciphertext_raw );
    file_put_contents($outputFile, $ciphertext);
}

// Decryption function
function decryptFile($inputFile, $outputFile, $key) {
    $ciphertext = file_get_contents($inputFile);
    $ciphertext = base64_decode($ciphertext);
    $ivlen = openssl_cipher_iv_length($cipher="AES-128-CBC");
    $iv = substr($ciphertext, 0, $ivlen);
    $hmac = substr($ciphertext, $ivlen, $sha2len=32);
    $ciphertext_raw = substr($ciphertext, $ivlen+$sha2len);
    $original_plaintext = openssl_decrypt($ciphertext_raw, $cipher, $key, $options=OPENSSL_RAW_DATA, $iv);
    $calcmac = hash_hmac('sha256', $ciphertext_raw, $key, $as_binary=true);
    if (hash_equals($hmac, $calcmac)) {
        file_put_contents($outputFile, $original_plaintext);
    }
}

// Example usage
$key = 'my-secret-key';
$inputFile = 'path/to/input/file';
$encryptedFile = 'path/to/encrypted/file';
$decryptedFile = 'path/to/decrypted/file';

// Encrypt file
encryptFile($inputFile, $encryptedFile, $key);

// Decrypt file
decryptFile($encryptedFile, $decryptedFile, $key);

In the code above, we define two functions: encryptFile and decryptFile. The encryptFile function takes an input file path, output file path, and encryption key as parameters. It reads the content of the input file, generates a random initialization vector (IV), encrypts the data using the AES-128-CBC cipher, and appends the IV and a message authentication code (MAC) to the encrypted data. The resulting ciphertext is then base64-encoded and written to the output file.

The decryptFile function takes an input file path, output file path, and encryption key as parameters. It reads the content of the input file, decodes the base64-encoded ciphertext, extracts the IV and MAC, decrypts the data using the same cipher and key, and verifies the MAC to ensure the integrity of the decrypted data. If the MAC is valid, the decrypted data is written to the output file.

To use these functions, you need to provide a key that will be used for encryption and decryption. You can also specify the input, encrypted, and decrypted file paths. You can call the encryptFile function to encrypt a file, and then call the decryptFile function to decrypt it.