(Excel) 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.

Download Excel Class Modules Chilkat Excel Class Modules

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

Dim crypt As Chilkat.Crypt2
Set crypt = Chilkat.NewCrypt2

' 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 Chilkat.Pfx
Set pfx = Chilkat.NewPfx

success = pfx.LoadPfxFile("qa_data/rsassa-pss/privatekey.pfx","PFX_PASSWORD")
If (success <> True) Then
    Debug.Print 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.)

Set cert = pfx.GetCert(0)
If (pfx.LastMethodSuccess <> True) Then
    Debug.Print pfx.LastErrorText
    Exit Sub
End If

Dim success As Boolean
success = 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

originalText = "This is a test"

pkcs7sig = crypt.SignStringENC(originalText)
Debug.Print "Detached Signature:"
Debug.Print 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.Print "Signature verified: "; success
success = crypt.VerifyStringENC("Not the original text",pkcs7sig)
Debug.Print "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.

opaqueSig = crypt.OpaqueSignStringENC(originalText)
Debug.Print "Opaque Signature:"
Debug.Print 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:

origTxt = crypt.OpaqueVerifyStringENC(opaqueSig)
If (crypt.LastMethodSuccess <> True) Then
    Debug.Print "Signature verification failed."
    Debug.Print crypt.LastErrorText

    Exit Sub
End If

Debug.Print "Signature verified."
Debug.Print "Extracted text:"; origTxt