(PureBasic) 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 PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkCrypt2.pb"
IncludeFile "CkCert.pb"

Procedure ChilkatExample()

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

    crypt.i = CkCrypt2::ckCreate()
    If crypt.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; 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.

    cert.i = CkCert::ckCreate()
    If cert.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; If the smartcard or token requires a PIN, we can set it here to avoid the dialog...
    CkCert::setCkSmartCardPin(cert, "000000")

    success.i = CkCert::ckLoadFromSmartcard(cert,"")
    If success <> 1
        Debug CkCert::ckLastErrorText(cert)
        CkCrypt2::ckDispose(crypt)
        CkCert::ckDispose(cert)
        ProcedureReturn
    EndIf

    ; Tell it to use the cert and private key we've loaded.
    success = CkCrypt2::ckSetSigningCert(crypt,cert)
    If success <> 1
        Debug CkCrypt2::ckLastErrorText(crypt)
        CkCrypt2::ckDispose(crypt)
        CkCert::ckDispose(cert)
        ProcedureReturn
    EndIf

    ; Indicate we want the opaque signature in base64 format:
    CkCrypt2::setCkEncodingMode(crypt, "base64")

    ; Sign the string using the "utf-8" byte representation:
    CkCrypt2::setCkCharset(crypt, "utf-8")

    ; Create the opaque signature:
    originalData.s = "This is the string to be signed."
    opaqueSig.s = CkCrypt2::ckOpaqueSignStringENC(crypt,originalData)
    If CkCrypt2::ckLastMethodSuccess(crypt) <> 1
        Debug CkCrypt2::ckLastErrorText(crypt)
        CkCrypt2::ckDispose(crypt)
        CkCert::ckDispose(cert)
        ProcedureReturn
    EndIf

    Debug opaqueSig

    ; 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...

    vCrypt.i = CkCrypt2::ckCreate()
    If vCrypt.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; 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.
    success = CkCrypt2::ckSetVerifyCert(vCrypt,cert)
    If success <> 1
        Debug CkCrypt2::ckLastErrorText(vCrypt)
        CkCrypt2::ckDispose(crypt)
        CkCert::ckDispose(cert)
        CkCrypt2::ckDispose(vCrypt)
        ProcedureReturn
    EndIf

    CkCrypt2::setCkEncodingMode(vCrypt, "base64")
    CkCrypt2::setCkCharset(vCrypt, "utf-8")

    extractedData.s = CkCrypt2::ckOpaqueVerifyStringENC(vCrypt,opaqueSig)
    If CkCrypt2::ckLastMethodSuccess(vCrypt) <> 1
        Debug CkCrypt2::ckLastErrorText(vCrypt)
        CkCrypt2::ckDispose(crypt)
        CkCert::ckDispose(cert)
        CkCrypt2::ckDispose(vCrypt)
        ProcedureReturn
    EndIf

    Debug "The extracted data: " + extractedData

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


    CkCrypt2::ckDispose(crypt)
    CkCert::ckDispose(cert)
    CkCrypt2::ckDispose(vCrypt)


    ProcedureReturn
EndProcedure