Xeo*_*oss 17 php smtp ssl-certificate starttls
为了防止中间人攻击(假装是其他人的服务器),我想验证我通过SSL连接的SMTP服务器是否有一个有效的SSL证书,证明它是我认为的.
例如,在端口25上连接到SMTP服务器后,我可以切换到安全连接,如下所示:
<?php
$smtp = fsockopen( "tcp://mail.example.com", 25, $errno, $errstr );
fread( $smtp, 512 );
fwrite($smtp,"HELO mail.example.me\r\n"); // .me is client, .com is server
fread($smtp, 512);
fwrite($smtp,"STARTTLS\r\n");
fread($smtp, 512);
stream_socket_enable_crypto( $smtp, true, STREAM_CRYPTO_METHOD_TLS_CLIENT );
fwrite($smtp,"HELO mail.example.me\r\n");
但是,没有提到PHP检查SSL证书的位置.PHP有一个内置的根CA列表吗？它只是接受任何东西吗？
什么是验证证书有效的正确方法,以及SMTP服务器真的是我认为的那个？
根据PHP.net上的这条评论,似乎我可以使用一些流选项进行SSL检查.最好的部分是stream_context_set_option接受上下文或流资源.因此,在TCP连接的某个时刻,您可以使用CA证书捆绑包切换到SSL .
$resource = fsockopen( "tcp://mail.example.com", 25, $errno, $errstr );
...
stream_set_blocking($resource, true);
stream_context_set_option($resource, 'ssl', 'verify_host', true);
stream_context_set_option($resource, 'ssl', 'verify_peer', true);
stream_context_set_option($resource, 'ssl', 'allow_self_signed', false);
stream_context_set_option($resource, 'ssl', 'cafile', __DIR__ . '/cacert.pem');
$secure = stream_socket_enable_crypto($resource, true, STREAM_CRYPTO_METHOD_TLS_CLIENT);
stream_set_blocking($resource, false);
if( ! $secure)
{
die("failed to connect securely\n");
}
但是,虽然这现在解决了主要问题 - 如何验证有效证书实际上属于我正在连接的域/ IP？
换句话说,我连接的服务器的证书也可能有一个有效的证书 - 但我怎么知道它对"example.com"有效,而不是另一台使用有效证书的服务器就像"example.com"一样？
您似乎可以使用steam context params 捕获SSL证书,并使用openssl_x509_parse解析它.
$cont = stream_context_get_params($r);
print_r(openssl_x509_parse($cont["options"]["ssl"]["peer_certificate"]));
更新:有更好的方法,请参阅评论.
您可以捕获证书并使用openssl过滤器与服务器进行对话.这样,您可以提取证书并在同一连接期间检查它.
这是一个不完整的实现(实际邮件发送的谈话是不存在的),这应该让你开始:
<?php
$server = 'smtp.gmail.com';
$pid = proc_open("openssl s_client -connect $server:25 -starttls smtp",
array(
0 => array('pipe', 'r'),
1 => array('pipe', 'w'),
2 => array('pipe', 'r'),
),
$pipes,
'/tmp',
array()
);
list($smtpout, $smtpin, $smtperr) = $pipes; unset($pipes);
$stage = 0;
$cert = 0;
$certificate = '';
while(($stage < 5) && (!feof($smtpin)))
{
$line = fgets($smtpin, 1024);
switch(trim($line))
{
case '-----BEGIN CERTIFICATE-----':
$cert = 1;
break;
case '-----END CERTIFICATE-----':
$certificate .= $line;
$cert = 0;
break;
case '---':
$stage++;
}
if ($cert)
$certificate .= $line;
}
fwrite($smtpout,"HELO mail.example.me\r\n"); // .me is client, .com is server
print fgets($smtpin, 512);
fwrite($smtpout,"QUIT\r\n");
print fgets($smtpin, 512);
fclose($smtpin);
fclose($smtpout);
fclose($smtperr);
proc_close($pid);
print $certificate;
$par = openssl_x509_parse($certificate);
?>
当然,在向服务器发送任何有意义的内容之前,您将移动证书解析和检查.
在$par数组中,您应该找到(在其余的)名称,同样解析为主题.
Array
(
[name] => /C=US/ST=California/L=Mountain View/O=Google Inc/CN=smtp.gmail.com
[subject] => Array
(
[C] => US
[ST] => California
[L] => Mountain View
[O] => Google Inc
[CN] => smtp.gmail.com
)
[hash] => 11e1af25
[issuer] => Array
(
[C] => US
[O] => Google Inc
[CN] => Google Internet Authority
)
[version] => 2
[serialNumber] => 280777854109761182656680
[validFrom] => 120912115750Z
[validTo] => 130607194327Z
[validFrom_time_t] => 1347451070
[validTo_time_t] => 1370634207
...
[extensions] => Array
(
...
[subjectAltName] => DNS:smtp.gmail.com
)
要检查有效性,除了日期检查等,SSL本身执行哪些操作,您必须验证这些条件是否适用:
实体的CN是您的DNS名称,例如"CN = smtp.your.server.com"
定义了扩展,它们包含一个subjectAltName,它一旦爆炸explode(',', $subjectAltName),就会生成一个带有DNS:前缀的记录数组,其中至少有一个与您的DNS名称相匹配.如果不匹配,则拒绝证书.
所以我决定深究这一点,并下载了OpenSSL的源代码(openssl-1.0.1c)并尝试自己查看.
我发现没有引用我期望的代码,即:
subjectAltName(OpenSSL调用SN_subject_alt_name)OpenSSL似乎将所有证书详细信息放入一个结构中,对其中一些进行非常基本的测试,但大多数"人类可读"的字段都是单独存在的.这是有道理的:可以说,名称检查比证书签名检查更高
然后我还下载了最新的cURL和最新的PHP tarball.
在PHP源代码中我什么都没找到; 显然任何选项都只是传递下去,否则就会被忽略.此代码运行时没有警告:
stream_context_set_option($smtp, 'ssl', 'I-want-a-banana', True);
然后stream_context_get_options尽职尽责地检索
[ssl] => Array
(
[I-want-a-banana] => 1
...
这也是有道理的:PHP在"上下文选项设置"环境中无法知道将使用哪些选项.
同样,证书解析代码解析证书并提取OpenSSL放在那里的信息,但它不验证相同的信息.
所以我挖得更深一点,最后在cURL中找到了证书验证码,这里:
// curl-7.28.0/lib/ssluse.c
static CURLcode verifyhost(struct connectdata *conn,
X509 *server_cert)
{
它按照我的预期执行:它查找subjectAltNames,它检查所有这些是否合理并运行它们过去hostmatch,运行hello.example.com ==*.example.com之类的检查.还有额外的健全性检查:"我们需要至少2个点模式,以避免过于宽泛的通配符匹配." 和xn--检查.
总而言之,OpenSSL运行一些简单的检查,并将其余的检查留给调用者.调用OpenSSL的cURL实现了更多检查.PHP也会在CN上运行一些检查verify_peer,但subjectAltName单独留下.这些检查并不能说服我太多; 见下文"测试".
由于缺乏访问cURL函数的能力,最好的替代方法是重新实现 PHP中的函数.
例如,可变通配符域匹配可以通过点扩展实际域和证书域来完成,从而反转两个阵列
com.example.site.my
com.example.*
并验证相应的项目是否相等,或证书一个是*; 如果发生这种情况,我们必须已经检查了至少两个组件,在这里com和example.
我相信如果您想一次性检查证书,上面的解决方案是最好的解决方案之一.更好的是能够直接打开流而不求助于openssl客户端 - 这是可能的 ; 看评论.
我有一份来自Thawte的优质,有效且完全信任的证书,发给"mail.eve.com".
然后,在Alice上运行的上述代码将安全地连接mail.eve.com,并且按预期连接.
现在我安装相同的证书mail.bob.com,或以其他方式我说服DNS我的服务器是Bob,而它实际上仍然是夏娃.
我希望SSL连接仍然有效(证书是有效和可信的),但该证书不颁发给鲍勃-它发放给夏娃.所以有人必须做最后一次检查,并警告爱丽丝,鲍勃实际上被夏娃模仿(或者等效地说,鲍勃正在使用夏娃的被盗证书).
我使用下面的代码:
$smtp = fsockopen( "tcp://mail.bob.com", 25, $errno, $errstr );
fread( $smtp, 512 );
fwrite($smtp,"HELO alice\r\n");
fread($smtp, 512);
fwrite($smtp,"STARTTLS\r\n");
fread($smtp, 512);
stream_set_blocking($smtp, true);
stream_context_set_option($smtp, 'ssl', 'verify_host', true);
stream_context_set_option($smtp, 'ssl', 'verify_peer', true);
stream_context_set_option($smtp, 'ssl', 'allow_self_signed', false);
stream_context_set_option($smtp, 'ssl', 'cafile', '/etc/ssl/cacert.pem');
$secure = stream_socket_enable_crypto($smtp, true, STREAM_CRYPTO_METHOD_TLS_CLIENT);
stream_set_blocking($smtp, false);
print_r(stream_context_get_options($smtp));
if( ! $secure)
die("failed to connect securely\n");
print "Success!\n";
和:
我认为这意味着,除非我犯了一些愚蠢的错误,否则PHP本身不会根据名称检查证书.
使用本文proc_open开头的代码,我再次可以连接,但这次我可以访问,subjectAltName因此可以自己检查,检测模仿.
为了不加载已经过长的内容，并且不再过多地讨论主题，请用更多文本来回答，我将其留给处理原因和原因的部分，在这里我将描述如何。
我针对 Google 和其他几个服务器测试了这段代码；有什么注释，嗯，代码中的注释。
<?php
$server = "smtp.gmail.com"; // Who I connect to
$myself = "my_server.example.com"; // Who I am
$cabundle = '/etc/ssl/cacert.pem'; // Where my root certificates are
// Verify server. There's not much we can do, if we suppose that an attacker
// has taken control of the DNS. The most we can hope for is that there will
// be discrepancies between the expected responses to the following code and
// the answers from the subverted DNS server.
// To detect these discrepancies though, implies we knew the proper response
// and saved it in the code. At that point we might as well save the IP, and
// decouple from the DNS altogether.
$match1 = false;
$addrs = gethostbynamel($server);
foreach($addrs as $addr)
{
$name = gethostbyaddr($addr);
if ($name == $server)
{
$match1 = true;
break;
}
}
// Here we must decide what to do if $match1 is false.
// Which may happen often and for legitimate reasons.
print "Test 1: " . ($match1 ? "PASSED" : "FAILED") . "\n";
$match2 = false;
$domain = explode('.', $server);
array_shift($domain);
$domain = implode('.', $domain);
getmxrr($domain, $mxhosts);
foreach($mxhosts as $mxhost)
{
$tests = gethostbynamel($mxhost);
if (0 != count(array_intersect($addrs, $tests)))
{
// One of the instances of $server is a MX for its domain
$match2 = true;
break;
}
}
// Again here we must decide what to do if $match2 is false.
// Most small ISP pass test 2; very large ISPs and Google fail.
print "Test 2: " . ($match2 ? "PASSED" : "FAILED") . "\n";
// On the other hand, if you have a PASS on a server you use,
// it's unlikely to become a FAIL anytime soon.
// End of maybe-they-help-maybe-they-don't checks.
// Establish the connection on SMTP port 25
$smtp = fsockopen( "tcp://{$server}", 25, $errno, $errstr );
fread( $smtp, 512 );
// Here you can check the usual banner from $server (or in general,
// check whether it contains $server's domain name, or whether the
// domain it advertises has $server among its MX's.
// But yet again, Google fails both these tests.
fwrite($smtp,"HELO {$myself}\r\n");
fread($smtp, 512);
// Switch to TLS
fwrite($smtp,"STARTTLS\r\n");
fread($smtp, 512);
stream_set_blocking($smtp, true);
stream_context_set_option($smtp, 'ssl', 'verify_peer', true);
stream_context_set_option($smtp, 'ssl', 'allow_self_signed', false);
stream_context_set_option($smtp, 'ssl', 'capture_peer_cert', true);
stream_context_set_option($smtp, 'ssl', 'cafile', $cabundle);
$secure = stream_socket_enable_crypto($smtp, true, STREAM_CRYPTO_METHOD_TLS_CLIENT);
stream_set_blocking($smtp, false);
$opts = stream_context_get_options($smtp);
if (!isset($opts['ssl']['peer_certificate'])) {
$secure = false;
} else {
$cert = openssl_x509_parse($opts['ssl']['peer_certificate']);
$names = '';
if ('' != $cert) {
if (isset($cert['extensions'])) {
$names = $cert['extensions']['subjectAltName'];
} elseif (isset($cert['subject'])) {
if (isset($cert['subject']['CN'])) {
$names = 'DNS:' . $cert['subject']['CN'];
} else {
$secure = false; // No exts, subject without CN
}
} else {
$secure = false; // No exts, no subject
}
}
$checks = explode(',', $names);
// At least one $check must match $server
$tmp = explode('.', $server);
$fles = array_reverse($tmp);
$okay = false;
foreach($checks as $check) {
$tmp = explode(':', $check);
if ('DNS' != $tmp[0]) continue; // candidates must start with DNS:
if (!isset($tmp[1])) continue; // and have something afterwards
$tmp = explode('.', $tmp[1]);
if (count($tmp) < 3) continue; // "*.com" is not a valid match
$cand = array_reverse($tmp);
$okay = true;
foreach($cand as $i => $item) {
if (!isset($fles[$i])) {
// We connected to www.example.com and certificate is for *.www.example.com -- bad.
$okay = false;
break;
}
if ($fles[$i] == $item) {
continue;
}
if ($item == '*') {
break;
}
}
if ($okay) {
break;
}
}
if (!$okay) {
$secure = false; // No hosts matched our server.
}
}
if (!$secure) {
die("failed to connect securely\n");
}
print "Success!\n";
// Continue with connection...