(PowerShell) Create PKCS7 Attached/Opaque Signature (S/MIME)

Create an S/MIME message with a PKCS7 attached/opaque signature.

Chilkat .NET Downloads Chilkat .NET Assemblies

Add-Type -Path "C:\chilkat\ChilkatDotNet47-9.5.0-x64\ChilkatDotNet47.dll"

# This example requires the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

$mime = New-Object Chilkat.Mime

# Load a certificate w/ private key for signing.
# There are many ways of getting a certificate object:
# from a pfx file, from .cer and private-key files, from the
# Windows registry-based certificate stores, etc.
# Load a PFX file into a certificate object.
$cert = New-Object Chilkat.Cert
$pfxFilepath = "pfxFiles/something.pfx"
$pfxPassword = "secret"
$success = $cert.LoadPfxFile($pfxFilepath,$pfxPassword)
if ($success -eq $false) {
    $($cert.LastErrorText)
    exit
}

# Create a very simple MIME message to be signed:
$success = $mime.AddHeaderField("Subject","This is a test")
$success = $mime.AddHeaderField("MyCustomHeader","abc123")
$mime.ContentType = "text/plain"
$mime.SetBody("This is a plain-text body.")

# Examine the MIME prior to signing:
$("--- MIME prior to signing ---")
$($mime.GetMime())

# The MIME prior to signing looks like this:
# -------------------------------------------------------------------------------

# Subject: This is a test
# MyCustomHeader: abc123
# Content-Type: text/plain
# 
# This is a plain-text body.

# -------------------------------------------------------------------------------

# The default hash algorithm used in the signing process is "SHA1".
# To change it, set the SigningHashAlg property:
$mime.SigningHashAlg = "SHA256"

# Convert the MIME to PKCS7 signed-data.
$success = $mime.ConvertToSigned($cert)
if ($success -eq $false) {
    $($mime.LastErrorText)
    exit
}

# Examine the signed MIME
$("--- MIME converted to PKCS7 signed-data ---")
$($mime.GetMime())

# The MIME after signing looks like this:
# -------------------------------------------------------------------------------

# Subject: This is a test
# MyCustomHeader: abc123
# Content-Disposition: attachment; filename="smime.p7m"
# Content-Transfer-Encoding: base64
# Content-Type: application/x-pkcs7-mime;
#  name="smime.p7m"; smime-type="signed-data"
# 
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# ------------------------------------------------------------------------------