(Classic ASP) 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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ActiveX for 32-bit and 64-bit Windows

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

' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.Crypt2")
set crypt = Server.CreateObject("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.)
' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.Pfx")
set pfx = Server.CreateObject("Chilkat.Pfx")
success = pfx.LoadPfxFile("qa_data/rsassa-pss/privatekey.pfx","PFX_PASSWORD")
If (success <> 1) Then
    Response.Write "<pre>" & Server.HTMLEncode( pfx.LastErrorText) & "</pre>"
    Response.End
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.)
' cert is a Chilkat.Cert
Set cert = pfx.GetCert(0)
If (pfx.LastMethodSuccess <> 1) Then
    Response.Write "<pre>" & Server.HTMLEncode( pfx.LastErrorText) & "</pre>"
    Response.End
End If

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)
Response.Write "<pre>" & Server.HTMLEncode( "Detached Signature:") & "</pre>"
Response.Write "<pre>" & Server.HTMLEncode( pkcs7sig) & "</pre>"

' 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)
Response.Write "<pre>" & Server.HTMLEncode( "Signature verified: " & success) & "</pre>"
success = crypt.VerifyStringENC("Not the original text",pkcs7sig)
Response.Write "<pre>" & Server.HTMLEncode( "Signature verified: " & success) & "</pre>"

' 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)
Response.Write "<pre>" & Server.HTMLEncode( "Opaque Signature:") & "</pre>"
Response.Write "<pre>" & Server.HTMLEncode( opaqueSig) & "</pre>"

' 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 <> 1) Then
    Response.Write "<pre>" & Server.HTMLEncode( "Signature verification failed.") & "</pre>"
    Response.Write "<pre>" & Server.HTMLEncode( crypt.LastErrorText) & "</pre>"

    Response.End
End If

Response.Write "<pre>" & Server.HTMLEncode( "Signature verified.") & "</pre>"
Response.Write "<pre>" & Server.HTMLEncode( "Extracted text:" & origTxt) & "</pre>"


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