Perl

Create an Opaque (Attached) S/MIME Signature

Demonstrates the Chilkat Mime.ConvertToSigned method, which creates an opaque (attached) S/MIME signature. The only argument is the signing Cert. On success the entity is replaced by a CMS/PKCS #7 signed-data structure that wraps the content inside the signature.

Note: The file paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: An opaque signature bundles the content inside the CMS structure, so the message is a single application/pkcs7-mime blob that only S/MIME-aware software can read. It is more tamper-resistant in transit — nothing can alter the content without breaking the wrapper — at the cost of the backward compatibility a detached signature offers. Use it when every recipient is known to support S/MIME.

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Chilkat2 Perl

use strict;
use warnings;
use Chilkat2;

my $mime = Chilkat2::Mime->new;
my $success = $mime->SetBodyFromPlainText('This message will be signed.');
if (!$success) {
    print $mime->LastErrorText, "\n";
    exit;
}

# Load the signing certificate (which must have access to its private key) from a PFX file.
# The PFX password should come from a secure source rather than being hard-coded.
my $pfxPassword = 'myPfxPassword';
my $cert = Chilkat2::Cert->new;
$success = $cert->LoadPfxFile('qa_data/signer.pfx', $pfxPassword);
if (!$success) {
    print $cert->LastErrorText, "\n";
    exit;
}

# Create an OPAQUE (attached) S/MIME signature.  The entity is replaced by a CMS/PKCS #7
# signed-data structure that wraps the content inside the signature.
$success = $mime->ConvertToSigned($cert);
if (!$success) {
    print $mime->LastErrorText, "\n";
    exit;
}

$success = $mime->SaveMime('qa_output/signed_opaque.eml');
if (!$success) {
    print $mime->LastErrorText, "\n";
    exit;
}

print "Message converted to an opaque signed message.\n";