(PureBasic) Create and Verify an Opaque PKCS7/CMS Signature

Demonstrates how 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 "CkCert.pb"
IncludeFile "CkPrivateKey.pb"
IncludeFile "CkCrypt2.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 PFX/.p12, Java keystore, JWK, Windows registry-based certificate stores, and other sources.
    ; This example will load the certificate from a .crt and the private key from a .key file

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

    ; The LoadFromFile method will automatically detect the format and load it.
    success.i = CkCert::ckLoadFromFile(cert,"qa_data/certs/test_12345678a.cer")
    If success <> 1
        Debug CkCert::ckLastErrorText(cert)
        CkCrypt2::ckDispose(crypt)
        CkCert::ckDispose(cert)
        ProcedureReturn
    EndIf

    ; Our private key is in an encrypted PKCS8 format.
    ; If you don't know the format of your key, but you do know it's encrypted,
    ; and requires a password, then just call any of the Chilkat methods that load
    ; a private key w/ a password argument.  Chilkat will auto-detect the format
    ; and load it correctly even if it's not the format indicated by the method name..
    privKey.i = CkPrivateKey::ckCreate()
    If privKey.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    password.s = "12345678a"
    success = CkPrivateKey::ckLoadPkcs8EncryptedFile(privKey,"qa_data/certs/test_12345678a.key",password)
    If success <> 1
        Debug CkPrivateKey::ckLastErrorText(privKey)
        CkCrypt2::ckDispose(crypt)
        CkCert::ckDispose(cert)
        CkPrivateKey::ckDispose(privKey)
        ProcedureReturn
    EndIf

    ; Set properties required for signing.

    ; Tell it to use the cert and private key we've loaded.
    success = CkCrypt2::ckSetSigningCert2(crypt,cert,privKey)
    If success <> 1
        Debug CkCrypt2::ckLastErrorText(crypt)
        CkCrypt2::ckDispose(crypt)
        CkCert::ckDispose(cert)
        CkPrivateKey::ckDispose(privKey)
        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)
        CkPrivateKey::ckDispose(privKey)
        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

    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)
        CkPrivateKey::ckDispose(privKey)
        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)
    CkPrivateKey::ckDispose(privKey)
    CkCrypt2::ckDispose(vCrypt)


    ProcedureReturn
EndProcedure