(Lianja) 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.

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

loCrypt = createobject("CkCrypt2")

// 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.

loCert = createobject("CkCert")

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

llSuccess = loCert.LoadFromSmartcard("")
if (llSuccess <> .T.) then
    ? loCert.LastErrorText
    release loCrypt
    release loCert
    return
endif

// Tell it to use the cert and private key we've loaded.
llSuccess = loCrypt.SetSigningCert(loCert)
if (llSuccess <> .T.) then
    ? loCrypt.LastErrorText
    release loCrypt
    release loCert
    return
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 <> .T.) then
    ? loCrypt.LastErrorText
    release loCrypt
    release loCert
    return
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...

loVCrypt = createobject("CkCrypt2")

// 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.
llSuccess = loVCrypt.SetVerifyCert(loCert)
if (llSuccess <> .T.) then
    ? loVCrypt.LastErrorText
    release loCrypt
    release loCert
    release loVCrypt
    return
endif

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

lcExtractedData = loVCrypt.OpaqueVerifyStringENC(lcOpaqueSig)
if (loVCrypt.LastMethodSuccess <> .T.) then
    ? loVCrypt.LastErrorText
    release loCrypt
    release loCert
    release loVCrypt
    return
endif

? "The extracted data: " + lcExtractedData

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


release loCrypt
release loCert
release loVCrypt