使用 OpenSSL 对大型文件进行对称加密和解密

PHP 缺少用于加密和解密大文件的内置函数。openssl_encrypt 可用于加密字符串，但将大文件加载到内存中是一个坏主意。

所以我们必须编写一个 userland 函数。此示例使用对称 AES-128-CBC 算法加密大文件的较小块并将其写入另一个文件。

加密文件

/**
 * 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;
}

解密文件

要解密使用上述功能加密的文件，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

如果你需要一个小片段来查看其工作原理或测试上述功能，请查看以下代码。

$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');

这将创建三个文件：

1. ** 带有纯文本的 testfile.txt
2. ** 带有加密文件的 testfile.txt.enc
3. ** 带解密文件的 testfile.txt.dec 。这应该与 testfile.txt 具有相同的内容 **