(Visual FoxPro) 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.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL loCrypt
LOCAL loPfx
LOCAL lnSuccess
LOCAL loCert
LOCAL lcOriginalText
LOCAL lcPkcs7sig
LOCAL lcOpaqueSig
LOCAL lcOrigTxt

* 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')
loCrypt = 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')
loPfx = CreateObject('Chilkat.Pfx')
lnSuccess = loPfx.LoadPfxFile("qa_data/rsassa-pss/privatekey.pfx","PFX_PASSWORD")
IF (lnSuccess <> 1) THEN
    ? loPfx.LastErrorText
    RELEASE loCrypt
    RELEASE loPfx
    CANCEL
ENDIF

* 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.)
loCert = loPfx.GetCert(0)
IF (loPfx.LastMethodSuccess <> 1) THEN
    ? loPfx.LastErrorText
    RELEASE loCrypt
    RELEASE loPfx
    CANCEL
ENDIF

loCrypt.SetSigningCert(loCert)

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

loCrypt.EncodingMode = "base64"

* Sign a string and return the base64 PKCS7 detached signature
lcOriginalText = "This is a test"
lcPkcs7sig = loCrypt.SignStringENC(lcOriginalText)
? "Detached Signature:"
? lcPkcs7sig

* 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:
lnSuccess = loCrypt.VerifyStringENC(lcOriginalText,lcPkcs7sig)
? "Signature verified: " + STR(lnSuccess)
lnSuccess = loCrypt.VerifyStringENC("Not the original text",lcPkcs7sig)
? "Signature verified: " + STR(lnSuccess)

* 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.
lcOpaqueSig = loCrypt.OpaqueSignStringENC(lcOriginalText)
? "Opaque Signature:"
? lcOpaqueSig

* 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:
lcOrigTxt = loCrypt.OpaqueVerifyStringENC(lcOpaqueSig)
IF (loCrypt.LastMethodSuccess <> 1) THEN
    ? "Signature verification failed."
    ? loCrypt.LastErrorText
    RELEASE loCert
    RELEASE loCrypt
    RELEASE loPfx
    CANCEL
ENDIF

? "Signature verified."
? "Extracted text:" + lcOrigTxt

RELEASE loCert

RELEASE loCrypt
RELEASE loPfx