(Visual FoxPro) A3/A4 Certificate to Create and Verify an Opaque PKCS7/CMS Signature

Demonstrates how to use an A3 or A4 certificate w/ private key on a smartcard or token to create a PKCS7 opaque signature, and also how to verify an opaque signature.

An opaque signature is different than a detached PKCS7 signature in that it contains the original data. Verifying an opaque signature retrieves the original content.

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

LOCAL loCrypt
LOCAL loCert
LOCAL lnSuccess
LOCAL lcOriginalData
LOCAL lcOpaqueSig
LOCAL loVCrypt
LOCAL lcExtractedData

* This example assumes the Chilkat API to have been previously unlocked.
* See Global Unlock Sample for sample code.

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Crypt2')
loCrypt = CreateObject('Chilkat.Crypt2')

* A certificate and private key is needed to create a signature.
* Chilkat provides many different ways to load a certificate and private key, such
* as from a smartcards and hardware tokens, PFX/.p12, Java keystore, JWK, Windows registry-based certificate stores, and other sources.
* This example will load the default certificate from the smartcard that is currently in
* the smartcard reader.

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Cert')
loCert = CreateObject('Chilkat.Cert')

* If the smartcard or token requires a PIN, we can set it here to avoid the dialog...
loCert.SmartCardPin = "000000"

lnSuccess = loCert.LoadFromSmartcard("")
IF (lnSuccess <> 1) THEN
    ? loCert.LastErrorText
    RELEASE loCrypt
    RELEASE loCert
    CANCEL
ENDIF

* Tell it to use the cert and private key we've loaded.
lnSuccess = loCrypt.SetSigningCert(loCert)
IF (lnSuccess <> 1) THEN
    ? loCrypt.LastErrorText
    RELEASE loCrypt
    RELEASE loCert
    CANCEL
ENDIF

* Indicate we want the opaque signature in base64 format:
loCrypt.EncodingMode = "base64"

* Sign the string using the "utf-8" byte representation:
loCrypt.Charset = "utf-8"

* Create the opaque signature:
lcOriginalData = "This is the string to be signed."
lcOpaqueSig = loCrypt.OpaqueSignStringENC(lcOriginalData)
IF (loCrypt.LastMethodSuccess <> 1) THEN
    ? loCrypt.LastErrorText
    RELEASE loCrypt
    RELEASE loCert
    CANCEL
ENDIF

? lcOpaqueSig

* The output looks like this:
* MIIPgQYJKoZIhvcNAQcCoIIPcjCCD24CAQExCzAJBgUrDgMCGgUAMC8GCSqGSIb3DQEHAaAiBCBUaGlzIGlzIHRoZSBzdHJpbmcgdG8gYmUgc...

* ----------------------------------------------------------------------------------------------
* Now let's verify the signature and retrieve the original data.
* We'll use a new Crypt2 object to keep things completely separate...

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Crypt2')
loVCrypt = CreateObject('Chilkat.Crypt2')

* We only need the certificate to verify a signature (and extract the data from
* an opaque signature).  The public key is always embedded within a certificate.
lnSuccess = loVCrypt.SetVerifyCert(loCert)
IF (lnSuccess <> 1) THEN
    ? loVCrypt.LastErrorText
    RELEASE loCrypt
    RELEASE loCert
    RELEASE loVCrypt
    CANCEL
ENDIF

loVCrypt.EncodingMode = "base64"
loVCrypt.Charset = "utf-8"

lcExtractedData = loVCrypt.OpaqueVerifyStringENC(lcOpaqueSig)
IF (loVCrypt.LastMethodSuccess <> 1) THEN
    ? loVCrypt.LastErrorText
    RELEASE loCrypt
    RELEASE loCert
    RELEASE loVCrypt
    CANCEL
ENDIF

? "The extracted data: " + lcExtractedData

* The output is:
* The extracted data: This is the string to be signed.

RELEASE loCrypt
RELEASE loCert
RELEASE loVCrypt