VB.NET

Decrypt S/MIME and Verify S/MIME Signatures

See more MIME Examples

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

Dim success As Boolean = False

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

Dim mime As New Chilkat.Mime

' Load an S/MIME message from a file:
success = mime.LoadMimeFile("signedMime.txt")
If (success = False) Then
    Debug.WriteLine(mime.LastErrorText)
    Exit Sub
End If


' The ContainsEncryptedParts/ContainsSignedParts methods
' can be called to determine if the MIME is encrypted and/or signed:
Dim isEncrypted As Boolean = mime.ContainsEncryptedParts()
Dim isSigned As Boolean = 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 <> True) Then
    ' UnwrapSecurity returns True if all signatures were
    ' verified and all parts decrypted.
    Debug.WriteLine(mime.LastErrorText)
    Exit Sub
End If


' 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 = True) Then
    Dim signerCert As New Chilkat.Cert

    ' 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 LastSignerCert with an index of 0:
    success = mime.LastSignerCert(0,signerCert)
    If (success = True) Then
        Debug.WriteLine("**** Signer Cert: " & signerCert.SubjectCN)
    End If

End If


' If the MIME was encrypted, get the certificate used for decryption
If (isEncrypted = True) Then
    ' The NumDecryptCerts property indicates how many certificates
    ' were used for decrypting.  This example will assume the value is 1.
    ' To get the 1st decrypt cert, call LastDecryptCert with an index of 0:
    Dim decryptCert As New Chilkat.Cert
    success = mime.LastDecryptCert(0,decryptCert)
    If (success = True) Then
        Debug.WriteLine("**** Decrypt Cert: " & decryptCert.SubjectCN)
    End If

End If


' Display the unwrapped MIME:
Debug.WriteLine(mime.GetMime())

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