How to Encrypt-Decrypt .pdf, .docx files in php?

Question

I am trying to encrypt/decrypt files in PHP. So far I am successful with .txt files but when it comes to .pdf and .doc or .docx my code fails, i.e. it gives absurd results. Can anyone suggest modification/alternative in my code? Thanks in advance!

Here's the encryption function

function encryptData($value)
{
   $key = "Mary has one cat";
   $text = $value;
   $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_ECB);
   $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
   $crypttext = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key, $text, MCRYPT_MODE_ECB, $iv);
   return $crypttext;
}

Here's the decryption function

function decryptData($value)
{
   $key = "Mary has one cat";
   $crypttext = $value;
   $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_ECB);
   $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
   $decrypttext = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, $crypttext, MCRYPT_MODE_ECB, $iv);
   return trim($decrypttext);
} 

Answer 1

I used this blog to help me encrypt/decrypt pdf files on my local machine using openssl_encrypt because mcrypt is deprecated in php7.

First, you get the file contents of the pdf:

$msg = file_get_contents('example.pdf');

Then I called the encryption function written in the blog post:

$msg_encrypted = my_encrypt($msg, $key);

Then I open the file I want to write to and write the new encrypted msg:

$file = fopen('example.pdf', 'wb');
fwrite($file, $msg_encrypted);
fclose($file);

For reference, in case that blog goes down, here are the encryption and decryption functions from the blog:

$key = 'bRuD5WYw5wd0rdHR9yLlM6wt2vteuiniQBqE70nAuhU=';

function my_encrypt($data, $key) {
    // Remove the base64 encoding from our key
    $encryption_key = base64_decode($key);
    // Generate an initialization vector
    $iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length('aes-256-cbc'));
    // Encrypt the data using AES 256 encryption in CBC mode using our encryption key and initialization vector.
    $encrypted = openssl_encrypt($data, 'aes-256-cbc', $encryption_key, 0, $iv);
    // The $iv is just as important as the key for decrypting, so save it with our encrypted data using a unique separator (::)
    return base64_encode($encrypted . '::' . $iv);
}



function my_decrypt($data, $key) {
    // Remove the base64 encoding from our key
    $encryption_key = base64_decode($key);
    // To decrypt, split the encrypted data from our IV - our unique separator used was "::"
    list($encrypted_data, $iv) = explode('::', base64_decode($data), 2);
    return openssl_decrypt($encrypted_data, 'aes-256-cbc', $encryption_key, 0, $iv);
}