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openssl_pkcs7_sign — Signieren einer S/MIME message
Die Funktion openssl_pkcs7_sign() signiert die Inhalte der Datei, angegeben durch den Pararmeter infilename. Beim Signieren wird das Zertifikat, angegeben durch signcert, und der dazu gehörige private Schlüssel privkey benutzt.
headers ist ein Array aus Headern die den Daten vorangestellt werden, nachdem diese signiert wurden (Für mehr Informationen über das Format dieses Parameters schauen Sie bei der Funktion openssl_pkcs7_encrypt() nach).
Der Parameter flags kann zur Änderung der Ausgabe benutzt werden - siehe PKCS7 Konstanten - falls nicht angegeben ist die Vorgabe PKCS7_DETACHED.
Der Parameter extracerts gibt den Namen einer Datei an, die ein oder mehrere extra Zertifikate enthält, die in die Unterschrift mit eingefügt werden. Das kann zum Beispiel als Hilfe für einen Empfänger dienen, das von Ihnen benutzte Zertifikat zu überprüfen.
Gibt bei Erfolg TRUE zurück. Im Fehlerfall wird FALSE zurückgegeben.
Beispiel #1 openssl_pkcs7_sign() Beispiel
<?php
// Die Nachricht die Sie unterschreiben möchten, damit der Empfänger sicher
// sein kann, dass diese Nachricht von ihnen stammt.
$data = <<<EOD
Sie haben meine Erlaubnis 10.000 EUR für Essen auszugeben.
Der CEO
EOD;
// Nachricht in einer Datei speichern
$fp = fopen("msg.txt", "w");
fwrite($fp, $data);
fclose($fp);
// verschlüsslen
if (openssl_pkcs7_sign("msg.txt", "signed.txt", "mycert.pem",
array("file://mycert.pem", "mypassphrase"),
array("To" => "joes@example.com", // keyed syntax
"From: HQ <ceo@example.com>", // indexed syntax
"Subject" => "Eyes only")
)) {
// Nachricht signiert - abschicken!
exec(ini_get("sendmail_path") . " < signed.txt");
}
?>
Amongst the many discussions about signing or encrypting email by itself, none really discuss the pain of having an email BOTH signed AND encrypted.
According to RFC 2311, you can encrypt then sign or sign then encrypt. However, it depends on the client in which you are programming for. In my experience, in Outlook 2000, it prefers it Encrypt then Sign. While in Outlook 2003, it is Sign then Encrypt. Generally, you want Sign then Encrypt, as it seems most logical from a snail-mail piece point of view. You first sign a letter than put it in an envelope. Certain clients complain if you do it in an order it does not like, so you may want to experiement with it.
When you perform the first function, do NOT put in any headers in the headers array parameters, you want to put it in the SECOND function you want to perform. If you put the headers in the first function, the second function will hide it from the mail servers. You do not want that. Here I will sign then encrypt.
<?php
// Setup mail headers.
$headers = array("To" => "someone@nowhere.net",
"From" => "noone@somewhere.net",
"Subject" => "A signed and encrypted message.");
// Sign the message first
openssl_pkcs7_sign("msg.txt","signed.txt",
"signing_cert.pem",array("private_key.pem",
"password"),array());
// Get the public key certificate.
$pubkey = file_get_contents("cert.pem");
//encrypt the message, now put in the headers.
openssl_pkcs7_encrypt("signed.txt", "enc.txt",
$pubkey,$headers,0,1);
$data = file_get_contents("enc.txt");
// separate header and body, to use with mail function
// unfortunate but required, else we have two sets of headers
// and the email client doesn't decode the attachment
$parts = explode("\n\n", $data, 2);
// send mail (headers in the Headers parameter will override those
// generated for the To & Subject parameters)
mail($mail, $subject, $parts[1], $parts[0]);
?>
Note that if you use a function that picks up the data from the disk to be used in another function in your program, remember that you may have used the explode("\n\n",$data,2) function which may have removed the spacing between the header and the message content.
When you take the signed message and feed it in to the encryption part, you have to remember that the line spacing must also be fed AS PART OF THE MESSAGE BODY! If you plan to sign then encrypt, do not feed the header output from the signing into the encrypting as part of the headers array parameter! The output of the signing should stay as part of the message body being encrypted. (And the same is true if you are doing the reverse of encrypting then signing.) An example of both the signing and encryption function made in to a routine for reusability, and then called to sign and encrypt a message.
THIS IS WRONG!:
<?php
// [0] of Array contains headers of message. [1] of Array contains signed body of message.
$signedOutputArray = signMessage($inputMessage,$headers);
// [0] of Array contains headers of message and the signing.
// [1] of Array contains encrypted body of message without the signing header.
$signedAndEncryptedArray = encryptMessage($signedOutputArray[1],
$signedOutputArray[0]);
mail($emailAddr,$subject,$signedAndEncryptedArray[1],
$signedAndEncryptedArray[0]);
?>
THIS IS CORRECT!
<?php
// [0] of Array contains headers of signing.
// [1] of Array contains signed body of message.
$signedOutputArray = signMessage($inputMessage,array());
// [0] of Array contains headers of message.
// [1] of Array contains encrypted contents of both the signed message and its headers of the signing.
$signedAndEncryptedArray =
encryptMessage($signedOutputArray[0] . "\n\n" . $signedOutputArray[1],$headers);
mail($emailAddr,$subject,$signedAndEncryptedArray[1],
$signedAndEncryptedArray[0]);
?>
I also spent hours when trying to find the reason of error:
"error getting private key".
Sometimes this error appeared, sometimes not.
My solution is using the realpath() for every parameter of openssl_pkcs7_sign. In my case the code looks like:
<?php
$Certif_path = 'certificate/mycertificate.pem';
$clearfile = "certificate/random_name";
$encfile = $clearfile . ".enc";
$clearfile = $clearfile . ".txt";
// ----
// -- fill $clearfile with the mail to be signed ...
// ----
openssl_pkcs7_sign(realpath($clearfile),
realpath('.').'/'.$encfile, // because $encfile does not exist yet we cannot use realpath($encfile);
'file://'.realpath($Certif_path),
array('file://'.realpath($Certif_path), PUBLIC_KEY),
array("To" => TO_EMAIL,
"From" => FROM_EMAIL,
"Subject" => ""),
PKCS7_DETACHED));
?>
I would like to make a modification from my previous note. Some clients prefer a certain order in which messages should be signed and encrypted (if both is desired). Newer email clients, such as Thunderbird and Outlook 2003 will accept the most secure method of "sign -> encrypt -> sign again".
Why?
The first signing authenticates the message saying that you did indeed write it. Then the email is encrypted so that only the recipient can open and read it. Then the second signing ensure confidentiality by identifying that the person encrypting is the one whom encrypted it, a message intended for the decrypting person. This is the most secure method. This ensures: Non-Repudiation of message (first sign), Confidentiality (encrypt), and Context Integrity [you were intended to be addressed] (second sign).
If you only sign then encrypt, there is no way you can guarantee that (aside from the contents of the letter, headers are placed in plain text outside the message) that the message was intended for you by the original sender. For example:
Bob signs a love letter and encrypts it to Amy saying only "I love you. -- Bob". Amy decrypts it, sees the message (and plays a joke) and forwards the message to John using John's public key, re-encrypting, but not tampering with the message contents keeping the signature valid. This allows Amy to make it look like Bob sent John a love letter and that Bob loves John, as you cannot verify whom sent it during encryption. That is not what you want!
This is also analogous to someone taking a government document, put it in an envelope themselves and write the government address in the return address and send it to you. You know the letter is written by the government, but you don't know for sure whether the government sent it to you directly or was opened and relayed.
While encrypting then signing has a problem, this is affectively signing on the envelope of a snail mail piece. I know you sent it, but is the message really from you? Or are you forwarding it?
Sign - Encrypt - Sign Again method will make the first sign show that you know the writer of the message is the person, encrypt it to keep others from reading it, sign again to indicate the message was not relayed and that the sender intended to sent the mail to address you.
Just make sure the headers of the mail is applied in the last step and not the second or third step.
For more information about the security and integrity risks of this situation, please read this web page: http://world.std.com/~dtd/sign_encrypt/sign_encrypt7.html
Working example:
<?php
$data = <<< EOF
Content-Type: text/plain;
charset="us-ascii"
Content-Transfer-Encoding: 7bit
You have my authorization to spend 10,000 on dinner expenses.
The CEO
EOF;
$fp = fopen("msg.txt", "w");
fwrite($fp, $data);
fclose($fp);
$headers = array("From" => "me@email.com");
openssl_pkcs7_sign("msg.txt", "signed.txt", "file://email.pem", array("file://email.pem", "123456"), $headers);
$data = file_get_contents("signed.txt");
$parts = explode("\n\n", $data, 2);
mail("you@email.com", "Signed message.", $parts[1], $parts[0]);
echo "Email sent";
?>
It is also possible to sign message including attachments. An easy way to do this:
<?php
$boundary = md5(uniqid(time()));
$boddy = "MIME-Version: 1.0\n";
$boddy .= "Content-Type: multipart/mixed; boundary=\"" . $boundary. "\"\n";
$boddy .= "Content-Transfer-Encoding: quoted-printable\n\n";
$boddy .= "This is a multi-part message in MIME format.\n\n";
$boddy .= "--$boundary\n";
$boddy .= "Content-Type: text/plain; charset=\"iso-8859-1\"\n";
$boddy .= "Content-Transfer-Encoding: quoted-printable\n\n";
$boddy .= $EmailText . "\n\n";
// Add the attachment to the message
do {
$boddy .= "--$boundary\n";
$boddy .= "Content-Type: application/pdf; name=\"FileName\"\n";
$boddy .= "Content-Transfer-Encoding: base64\n";
$boddy .= "Content-Disposition: attachment;\n\n";
$boddy .= chunk_split(base64_encode($file)) . "\n\n";
} while ( {files left to be attached} );
$boddy .= "--$boundary--\n";
// Save message to a file
$msg = 'msg.txt';
$signed = 'signed.txt';
$fp = fopen($msg, "w");
fwrite($fp, $boddy);
fclose($fp);
// Sign it
if (openssl_pkcs7_sign($msg, $signed, 'file://cert.pem',
array('file://key.pem', 'test'),
array("To" => "joes@example.com", // keyed syntax
"From: HQ <ceo@example.com>", // indexed syntax
"Subject" => "Eyes only"), PKCS7_DETACHED, 'intermediate_cert.pem' )) {
exec(ini_get('sendmail_path') . ' < ' . $signed);
}
?>
The same can be established by using the PEAR package Mail_Mime in combination with openssl_pkcs7_sign.
This command doesn't work correctly on WIN32 with IIS. Mails aren’t interpreted correctly by IIS SMTP Server (and by Outlook too). The reason is that UNIX and WINDOWS interpret the “enter to the next line” ascii code in a different way.
Below I present an improved code:
<?php
$data = <<<EOD
Testing 123
This is a test
Test
EOD;
//save the message to a file
$fp = fopen("msg.txt","w");
fwrite($fp,$data);
fclose($fp);
//sign the message using the sender's keys
openssl_pkcs7_sign("msg.txt", "signed.eml", "file://c:/max/cert.pem",
array("file://c:/max/priv.pem","your_password"),
array("To" => "recipient <recipients@mail.com>",
"From" => "sender <sender@mail.com>",
"Subject" => "Order Notification - Test"),PKCS7_DETACHED,"c:\max\extra_cert.pem");
$file_arry = file("signed.eml");
$file = join ("", $file_arry);
$message = preg_replace("/\r\n|\r|\n/", "\r\n", $file);
$fp = fopen("c:\Inetpub\mailroot\Pickup\signed.eml", "wb");
flock($fp, 2);
fputs($fp, $message);
flock($fp, 3);
fclose($fp);
?>
Besides, if you want to use the keys created with Windows, you should export them (from IE) to the form of PKCS#12 file (*.pfx).
Install OpenSSLWin32 from
http://www.shininglightpro.com/search.php?searchname=Win32+OpenSSL
execute: openssl.exe
enter the commands:
pkcs12 -in <pfx-file> -nokeys -out <pem-certs-file>
pkcs12 -in <pfx-file> -nocerts -nodes -out <pem-key-file>
Next export from IE Root CA certificate as Base-64 *.cer and rename the file to *.pem
And that's all!
It's probably worth noting that I had a great deal of difficulty getting either Mozilla 1.4 or Outlook Express 6 to verify signatures generated by openssl_pkcs7_sign() until I added a newline (\n) to the beginning of the message I was signing. Not sure why that is, but as soon as I made that change all problems disappeared.
The "mycert.pem" parameters as shown in the example above are not correct. You either have to pass a string containing the PEM encoded certificate or key, or the location of a file in file://path/to/file.pem notation. See the comments on the OpenSSL functions page (the page above this one).
If you want to integrate PKCS7 signing/verifying with a browser and it's not a problem that it's only Internet Explorer (or Netscape + ActiveX plugin) you can look at Capicom. It's a free component and available at the MSDN website.
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