(Xojo Plugin) 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
success = pfx.LoadPfxFile("qa_data/rsassa-pss/privatekey.pfx","PFX_PASSWORD")
If (success <> True) Then
    System.DebugLog(pfx.LastErrorText)
    Return
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
cert = pfx.GetCert(0)
If (pfx.LastMethodSuccess <> True) Then
    System.DebugLog(pfx.LastErrorText)
    Return
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
Dim originalText As String
originalText = "This is a test"
Dim pkcs7sig As String
pkcs7sig = crypt.SignStringENC(originalText)
System.DebugLog("Detached Signature:")
System.DebugLog(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)
System.DebugLog("Signature verified: " + Str(success))
success = crypt.VerifyStringENC("Not the original text",pkcs7sig)
System.DebugLog("Signature verified: " + Str(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
opaqueSig = crypt.OpaqueSignStringENC(originalText)
System.DebugLog("Opaque Signature:")
System.DebugLog(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
origTxt = crypt.OpaqueVerifyStringENC(opaqueSig)
If (crypt.LastMethodSuccess <> True) Then
    System.DebugLog("Signature verification failed.")
    System.DebugLog(crypt.LastErrorText)

    Return
End If

System.DebugLog("Signature verified.")
System.DebugLog("Extracted text:" + origTxt)