sodium_crypto_secretstream_xchacha20poly1305_init_pull

<?php
function decrypt_file(string $inputFilePath, string $outputFilePath, string $key): void
{
    $inputFile = fopen($inputFilePath, 'rb');
    $outputFile = fopen($outputFilePath, 'wb');
    $header = fread($inputFile, 24);

    $state = sodium_crypto_secretstream_xchacha20poly1305_init_pull($header, $key);
    $inputFileSize = fstat($inputFile)['size'];

    // Decrypt the file and write its contents to the output file:
    for ($i = 24; $i < $inputFileSize; $i += 8192) {
        $ctxt_chunk = fread($inputFile, 8192);

        // We're not using $tag, but in real protocols you can use this on encrypt to e.g.
        // trigger a re-key or indicate the end of file. Then, on decrypt, you can assert
        // this behavior.
        [$ptxt_chunk, $tag] = sodium_crypto_secretstream_xchacha20poly1305_pull($state, $ctxt_chunk);
        fwrite($outputFile, $ptxt_chunk);
    }

    sodium_memzero($state);
    fclose($inputFile);
    fclose($outputFile);
}

// sodium_crypto_secretstream_xchacha20poly1305_keygen()
$key = sodium_base642bin('MS0lzb7HC+thY6jY01pkTE/cwsQxnRq0/2L1eL4Hxn8=', SODIUM_BASE64_VARIANT_ORIGINAL);

$example = sodium_hex2bin('971e33b255f0990ef3931caf761c59136efa77b434832f28ec719e3ff73f5aec38b3bba1574ab5b70a8844d8da36a668e802cfea2c');
file_put_contents('hello.enc', $example);
decrypt_file('hello.enc', 'hello.txt.decrypted', $key);
var_dump(file_get_contents('hello.txt.decrypted'));
?>