Sign an S/MIME message

# openssl_pkcs7_sign

(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)

openssl_pkcs7_sign — Sign an S/MIME message

### Description

openssl_pkcs7_sign(
string `$input_filename`,
string `$output_filename`,
OpenSSLCertificate|string `$certificate`,
#[\SensitiveParameter] OpenSSLAsymmetricKey|OpenSSLCertificate|array|string `$private_key`,
?array `$headers`,
int `$flags` = `PKCS7_DETACHED`,
?string `$untrusted_certificates_filename` = `null`
): bool

openssl_pkcs7_sign() takes the contents of the file named `input_filename` and signs them using the certificate and its matching private key specified by `certificate` and `private_key` parameters.

### Parameters

`input_filename`

  The input file you are intending to digitally sign.

`output_filename`

  The file which the digital signature will be written to.

`certificate`

  The X.509 certificate used to digitally sign `input_filename`. See Key/Certificate parameters for a list of valid values.

`private_key`

  `private_key` is the private key corresponding to `certificate`. See Public/Private Key parameters for a list of valid values.

`headers`

  `headers` is an array of headers that will be prepended to the data after it has been signed (see openssl_pkcs7_encrypt() for more information about the format of this parameter).

`flags`

  `flags` can be used to alter the output - see PKCS7 constants.

`untrusted_certificates_filename`

  `untrusted_certificates_filename` specifies the name of a file containing a bunch of extra certificates to include in the signature which can for example be used to help the recipient to verify the certificate that you used.

### Return Values

Returns `true` on success or `false` on failure.

### Changelog

Version | Description
--- | ---
8.0.0 | `certificate` accepts an OpenSSLCertificate instance now; previously, a resource of type `OpenSSL X.509 CSR` was accepted.
8.0.0 | `private_key` accepts an OpenSSLAsymmetricKey or OpenSSLCertificate instance now; previously, a resource of type `OpenSSL key` or `OpenSSL X.509 CSR` was accepted.

### Examples

Example #1 openssl_pkcs7_sign() example

`<?php
// the message you want to sign so that recipient can be sure it was you that
// sent it
$data = <<<EOD
You have my authorization to spend $10,000 on dinner expenses.
The CEO
EOD;
// save message to file
$fp = fopen("msg.txt", "w");
fwrite($fp, $data);
fclose($fp);
// encrypt it
if (openssl_pkcs7_sign("msg.txt", "signed.txt", "file://mycert.pem",
array("file://mycert.pem", "mypassphrase"),
array("To" => "joes@example.com", // keyed syntax
"From: HQ <ceo@example.com>", // indexed syntax
"Subject" => "Eyes only")
)) {
// message signed - send it!
exec(ini_get("sendmail_path") . " < signed.txt");
}
?>`
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