(VB.NET) RSASSA-PSS Sign String to Create Base64 PCKS7 Signature

Signs a string to create a PKCS7 signature in the base64 encoding. The signature algorithm is RSASSA-PSS with SHA256.

Note: This example requires Chilkat v9.5.0.67 or greater.

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

Dim crypt As New Chilkat.Crypt2

' Get a digital certificate with private key from a .pfx
' (Chilkat has many different ways to provide a cert + private key for siging.
' Using a PFX is just one possible option.)
Dim pfx As New Chilkat.Pfx
Dim success As Boolean = pfx.LoadPfxFile("qa_data/rsassa-pss/privatekey.pfx","PFX_PASSWORD")
If (success <> True) Then
    Debug.WriteLine(pfx.LastErrorText)
    Exit Sub
End If


' Get the certificate to be used for signing.
' (The typical case for a PFX is that it contains a cert with an associated private key,
' as well as other certificates in the chain of authentication.  The cert with the private
' key should be in the first position at index 0.)
Dim cert As Chilkat.Cert = pfx.GetCert(0)
If (pfx.LastMethodSuccess <> True) Then
    Debug.WriteLine(pfx.LastErrorText)
    Exit Sub
End If

crypt.SetSigningCert(cert)

' Indicate that RSASSA-PSS with SHA256 should be used.
crypt.SigningAlg = "pss"
crypt.HashAlgorithm = "sha256"


crypt.EncodingMode = "base64"

' Sign a string and return the base64 PKCS7 detached signature
Dim originalText As String = "This is a test"
Dim pkcs7sig As String = crypt.SignStringENC(originalText)
Debug.WriteLine("Detached Signature:")
Debug.WriteLine(pkcs7sig)

' This signature looks like this:
' MIIG5wYJKoZIhvcNAQcCoIIG2DCCBtQCAQExDzANBgl .. YToLqEwTdU87ox5g7rvw==

' The ASN.1 of the signature can be examined by browsing to https://lapo.it/asn1js/ ,
' then copy-and-paste the Base64 signature into the form and decode..

' The signature can be verified against the original data like this:
success = crypt.VerifyStringENC(originalText,pkcs7sig)
Debug.WriteLine("Signature verified: " & success)
success = crypt.VerifyStringENC("Not the original text",pkcs7sig)
Debug.WriteLine("Signature verified: " & success)


' Now we'll create an opaque signature (the opposite of a detached signature). 
' An opaque signature is a PKCS7 message that contains both the original data and
' the signature.  The verification process extracts the original data.
Dim opaqueSig As String = crypt.OpaqueSignStringENC(originalText)
Debug.WriteLine("Opaque Signature:")
Debug.WriteLine(opaqueSig)

' The ASN.1 of the signature can be examined by browsing to https://lapo.it/asn1js/ ,
' then copy-and-paste the Base64 signature into the form and decode..

' We can verify and extract the original data:
Dim origTxt As String = crypt.OpaqueVerifyStringENC(opaqueSig)
If (crypt.LastMethodSuccess <> True) Then
    Debug.WriteLine("Signature verification failed.")
    Debug.WriteLine(crypt.LastErrorText)

    Exit Sub
End If


Debug.WriteLine("Signature verified.")
Debug.WriteLine("Extracted text:" & origTxt)