security.php

<?php

//generate dh key using alice private key
function generateDHKey_alice($remote_public_key){
  $keyfile="file://".__DIR__.DIRECTORY_SEPARATOR."alice_privatekey.pem"; //absolute path
  $local_priv_key = openssl_pkey_get_private($keyfile); //get server private key
  $shared_secret = openssl_dh_compute_key(hex2bin($remote_public_key), $local_priv_key); // get dh key
  return $shared_secret;
}

//generate dh key using bob private key
function generateDHKey_bob($remote_public_key){
  $keyfile="file://".__DIR__.DIRECTORY_SEPARATOR."bob_privatekey.pem"; //absolute path
  $local_priv_key = openssl_pkey_get_private($keyfile); //get server private key
  $shared_secret = openssl_dh_compute_key(hex2bin($remote_public_key), $local_priv_key); // get dh key
  return $shared_secret;
}
//encrypt function
function encryptthis($data, $key) {
$encryption_key = base64_decode($key);
$iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length('aes-256-cbc'));
$encrypted = openssl_encrypt($data, 'aes-256-cbc', $encryption_key, 0, $iv);
return base64_encode($encrypted . '::' . $iv);
}

//DECRYPT FUNCTION
function decryptthis($data, $key) {
$encryption_key = base64_decode($key);
list($encrypted_data, $iv) = array_pad(explode('::', base64_decode($data), 2),2,null);
return openssl_decrypt($encrypted_data, 'aes-256-cbc', $encryption_key, 0, $iv);
}


define('FILE_ENCRYPTION_BLOCKS', 10000);

/**
 * Encrypt the passed file and saves the result in a new file with ".enc" as suffix.
 *
 * @param string $source Path to file that should be encrypted
 * @param string $key    The key used for the encryption
 * @param string $dest   File name where the encryped file should be written to.
 * @return string|false  Returns the file name that has been created or FALSE if an error occured
 */
function encryptFile($source, $key, $dest)
{
    $key = substr(sha1($key, true), 0, 16);
    $iv = openssl_random_pseudo_bytes(16);

    $error = false;
    if ($fpOut = fopen($dest, 'w')) {
        // Put the initialzation vector to the beginning of the file
        fwrite($fpOut, $iv);
        if ($fpIn = fopen($source, 'rb')) {
            while (!feof($fpIn)) {
                $plaintext = fread($fpIn, 16 * FILE_ENCRYPTION_BLOCKS);
                $ciphertext = openssl_encrypt($plaintext, 'AES-256-CBC', $key, OPENSSL_RAW_DATA, $iv);
                // Use the first 16 bytes of the ciphertext as the next initialization vector
                $iv = substr($ciphertext, 0, 16);
                fwrite($fpOut, $ciphertext);
            }
            fclose($fpIn);
        } else {
            $error = true;
        }
        fclose($fpOut);
    } else {
        $error = true;
    }

    //return $error ? false : $dest;
}

/**
 * Dencrypt the passed file and saves the result in a new file, removing the
 * last 4 characters from file name.
 *
 * @param string $source Path to file that should be decrypted
 * @param string $key    The key used for the decryption (must be the same as for encryption)
 * @param string $dest   File name where the decryped file should be written to.
 * @return string|false  Returns the file name that has been created or FALSE if an error occured
 */
function decryptFile($source, $key, $dest)
{
    $key = substr(sha1($key, true), 0, 16);

    $error = false;
    if ($fpOut = fopen($dest, 'w')) {
        if ($fpIn = fopen($source, 'rb')) {
            // Get the initialzation vector from the beginning of the file
            $iv = fread($fpIn, 16);
            while (!feof($fpIn)) {
                $ciphertext = fread($fpIn, 16 * (FILE_ENCRYPTION_BLOCKS + 1)); // we have to read one block more for decrypting than for encrypting
                $plaintext = openssl_decrypt($ciphertext, 'AES-256-CBC', $key, OPENSSL_RAW_DATA, $iv);
                // Use the first 16 bytes of the ciphertext as the next initialization vector
                $iv = substr($ciphertext, 0, 16);
                fwrite($fpOut, $plaintext);
            }
            fclose($fpIn);
        } else {
            $error = true;
        }
        fclose($fpOut);
    } else {
        $error = true;
    }

    //return $error ? false : $dest;
}