<?php
/*
* This file is part of the Symfony package.
*
* (c) Fabien Potencier <fabien@symfony.com>
*
* For the full copyright and license information, please view the LICENSE
* file that was distributed with this source code.
*/
namespace Symfony\Component\Mime\Crypto;
use Symfony\Component\Mime\Exception\InvalidArgumentException;
use Symfony\Component\Mime\Exception\RuntimeException;
use Symfony\Component\Mime\Header\UnstructuredHeader;
use Symfony\Component\Mime\Message;
use Symfony\Component\Mime\Part\AbstractPart;
/**
* @author Fabien Potencier <fabien@symfony.com>
*
* RFC 6376 and 8301
*/
final class DkimSigner
{
public const CANON_SIMPLE = 'simple';
public const CANON_RELAXED = 'relaxed';
public const ALGO_SHA256 = 'rsa-sha256';
public const ALGO_ED25519 = 'ed25519-sha256'; // RFC 8463
private \OpenSSLAsymmetricKey $key;
private string $domainName;
private string $selector;
private array $defaultOptions;
/**
* @param string $pk The private key as a string or the path to the file containing the private key, should be prefixed with file:// (in PEM format)
* @param string $passphrase A passphrase of the private key (if any)
*/
public function __construct(string $pk, string $domainName, string $selector, array $defaultOptions = [], string $passphrase = '')
{
if (!\extension_loaded('openssl')) {
throw new \LogicException('PHP extension "openssl" is required to use DKIM.');
}
$this->key = openssl_pkey_get_private($pk, $passphrase) ?: throw new InvalidArgumentException('Unable to load DKIM private key: '.openssl_error_string());
$this->domainName = $domainName;
$this->selector = $selector;
$this->defaultOptions = $defaultOptions + [
'algorithm' => self::ALGO_SHA256,
'signature_expiration_delay' => 0,
'body_max_length' => \PHP_INT_MAX,
'body_show_length' => false,
'header_canon' => self::CANON_RELAXED,
'body_canon' => self::CANON_RELAXED,
'headers_to_ignore' => [],
];
}
public function sign(Message $message, array $options = []): Message
{
$options += $this->defaultOptions;
if (!\in_array($options['algorithm'], [self::ALGO_SHA256, self::ALGO_ED25519], true)) {
throw new InvalidArgumentException(\sprintf('Invalid DKIM signing algorithm "%s".', $options['algorithm']));
}
$headersToIgnore['return-path'] = true;
$headersToIgnore['x-transport'] = true;
foreach ($options['headers_to_ignore'] as $name) {
$headersToIgnore[strtolower($name)] = true;
}
unset($headersToIgnore['from']);
$signedHeaderNames = [];
$headerCanonData = '';
$headers = $message->getPreparedHeaders();
foreach ($headers->getNames() as $name) {
foreach ($headers->all($name) as $header) {
if (isset($headersToIgnore[strtolower($header->getName())])) {
continue;
}
if ('' !== $header->getBodyAsString()) {
$headerCanonData .= $this->canonicalizeHeader($header->toString(), $options['header_canon']);
$signedHeaderNames[] = $header->getName();
}
}
}
[$bodyHash, $bodyLength] = $this->hashBody($message->getBody(), $options['body_canon'], $options['body_max_length']);
$params = [
'v' => '1',
'q' => 'dns/txt',
'a' => $options['algorithm'],
'bh' => base64_encode($bodyHash),
'd' => $this->domainName,
'h' => implode(': ', $signedHeaderNames),
'i' => '@'.$this->domainName,
's' => $this->selector,
't' => time(),
'c' => $options['header_canon'].'/'.$options['body_canon'],
];
if ($options['body_show_length']) {
$params['l'] = $bodyLength;
}
if ($options['signature_expiration_delay']) {
$params['x'] = $params['t'] + $options['signature_expiration_delay'];
}
$value = '';
foreach ($params as $k => $v) {
$value .= $k.'='.$v.'; ';
}
$value = trim($value);
$header = new UnstructuredHeader('DKIM-Signature', $value);
$headerCanonData .= rtrim($this->canonicalizeHeader($header->toString()."\r\n b=", $options['header_canon']));
if (self::ALGO_SHA256 === $options['algorithm']) {
if (!openssl_sign($headerCanonData, $signature, $this->key, \OPENSSL_ALGO_SHA256)) {
throw new RuntimeException('Unable to sign DKIM hash: '.openssl_error_string());
}
} else {
throw new \RuntimeException(\sprintf('The "%s" DKIM signing algorithm is not supported yet.', self::ALGO_ED25519));
}
$header->setValue($value.' b='.trim(chunk_split(base64_encode($signature), 73, ' ')));
$headers->add($header);
return new Message($headers, $message->getBody());
}
private function canonicalizeHeader(string $header, string $headerCanon): string
{
if (self::CANON_RELAXED !== $headerCanon) {
return $header."\r\n";
}
$exploded = explode(':', $header, 2);
$name = strtolower(trim($exploded[0]));
$value = str_replace("\r\n", '', $exploded[1]);
$value = trim(preg_replace("/[ \t][ \t]+/", ' ', $value));
return $name.':'.$value."\r\n";
}
private function hashBody(AbstractPart $body, string $bodyCanon, int $maxLength): array
{
$hash = hash_init('sha256');
$relaxed = self::CANON_RELAXED === $bodyCanon;
$currentLine = '';
$emptyCounter = 0;
$isSpaceSequence = false;
$length = 0;
foreach ($body->bodyToIterable() as $chunk) {
$canon = '';
for ($i = 0, $len = \strlen($chunk); $i < $len; ++$i) {
switch ($chunk[$i]) {
case "\r":
break;
case "\n":
// previous char is always \r
if ($relaxed) {
$isSpaceSequence = false;
}
if ('' === $currentLine) {
++$emptyCounter;
} else {
$currentLine = '';
$canon .= "\r\n";
}
break;
case ' ':
case "\t":
if ($relaxed) {
$isSpaceSequence = true;
break;
}
// no break
default:
if ($emptyCounter > 0) {
$canon .= str_repeat("\r\n", $emptyCounter);
$emptyCounter = 0;
}
if ($isSpaceSequence) {
$currentLine .= ' ';
$canon .= ' ';
$isSpaceSequence = false;
}
$currentLine .= $chunk[$i];
$canon .= $chunk[$i];
}
}
if ($length + \strlen($canon) >= $maxLength) {
$canon = substr($canon, 0, $maxLength - $length);
$length += \strlen($canon);
hash_update($hash, $canon);
break;
}
$length += \strlen($canon);
hash_update($hash, $canon);
}
// Add trailing Line return if last line is non empty
if ('' !== $currentLine) {
hash_update($hash, "\r\n");
$length += \strlen("\r\n");
}
if (!$relaxed && 0 === $length) {
hash_update($hash, "\r\n");
$length = 2;
}
return [hash_final($hash, true), $length];
}
}
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