(PowerShell) Decrypt S/MIME and Verify S/MIME Signatures

PowerShell example to decrypt S/MIME and verify S/MIME signatures. The S/MIME is unwrapped to get the original MIME prior to signing/encrypting.

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 an S/MIME message from a file:
$success = $mime.LoadMimeFile("signedMime.txt")
if ($success -ne $true) {
    $($mime.LastErrorText)
    exit
}

# The ContainsEncryptedParts/ContainsSignedParts methods
# can be called to determine if the MIME is encrypted and/or signed:
$isEncrypted = $mime.ContainsEncryptedParts()
$isSigned = $mime.ContainsSignedParts()

# We don't want the "unwrap extras".  You'll see what those
# are in a few moments...
$mime.UnwrapExtras = $false

# To verify the signature, call UnwrapSecurity.  This will
# verify the signature(s) and decrypt the S/MIME and restore
# the MIME to the unsigned/unencrypted state.
# The results of what was found are present in the MIME object's
# properties, as well as extra header fields that are added
# to the unwrapped MIME.
$success = $mime.UnwrapSecurity()
if ($success -ne $true) {
    # UnwrapSecurity returns $true if all signatures were
    # verified and all parts decrypted.
    $($mime.LastErrorText)
    exit
}

# The mime.UnwrapExtras property controls whether or not
# these additional fields are added to the unwrapped MIME:
# 
# X-NumPartsSigned: 1
# X-SignaturesValid: yes
# X-NumPartsEncrypted: 1
# X-Decrypted: no
# 
# The X-NumPartsSigned/X-SignaturesValid headers are added
# if the MIME was signed.  
# 
# The X-NumPartsEncrypted/X-Decrypted headers are added
# if the MIME was encrypted.
# 

# If the MIME was signed, get the certificate used for signing.
if ($isSigned -eq $true) {
    # The NumSignerCerts property indicates how many certificates
    # were used for signing.  This example will assume the value is 1.
    # To get the 1st signer cert, call GetSignerCert with an index of 0:
    $signerCert = $mime.GetSignerCert(0)
    if ($mime.LastMethodSuccess -eq $true) {
        $("**** Signer Cert: " + $signerCert.SubjectCN)

    }

}

# If the MIME was encrypted, get the certificate used for encryption:
if ($isEncrypted -eq $true) {
    # The NumEncryptCerts property indicates how many certificates
    # were used for encrypting.  This example will assume the value is 1.
    # To get the 1st encrypt cert, call GetEncryptCert with an index of 0:
    $encryptCert = $mime.GetEncryptCert(0)
    if ($mime.LastMethodSuccess -eq $true) {
        $("**** Encrypt Cert: " + $encryptCert.SubjectCN)

    }

}

# Display the unwrapped MIME:
$($mime.GetMime())

# Save the unwrapped MIME to a file:
$success = $mime.SaveMime("unwrappedMime.txt")