使用 OpenSSL 對大型檔案進行對稱加密和解密

PHP 缺少用於加密和解密大檔案的內建函式。openssl_encrypt 可用於加密字串，但將大檔案載入到記憶體中是一個壞主意。

所以我們必須編寫一個 userland 函式。此示例使用對稱 AES-128-CBC 演算法加密大檔案的較小塊並將其寫入另一個檔案。

加密檔案

/**
 * Define the number of blocks that should be read from the source file for each chunk.
 * For 'AES-128-CBC' each block consist of 16 bytes.
 * So if we read 10,000 blocks we load 160kb into memory. You may adjust this value
 * to read/write shorter or longer chunks.
 */
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-128-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;
}

解密檔案

要解密使用上述功能加密的檔案，你可以使用此功能。

/**
 * 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-128-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;
}

如何使用

如果你需要一個小片段來檢視其工作原理或測試上述功能，請檢視以下程式碼。

$fileName = __DIR__.'/testfile.txt';
$key = 'my secret key';
file_put_contents($fileName, 'Hello World, here I am.');
encryptFile($fileName, $key, $fileName . '.enc');
decryptFile($fileName . '.enc', $key, $fileName . '.dec');

這將建立三個檔案：

1. ** 帶有純文字的 testfile.txt
2. ** 帶有加密檔案的 testfile.txt.enc
3. ** 帶解密檔案的 testfile.txt.dec 。這應該與 testfile.txt 具有相同的內容 **