PureBasic

Create and Verify an Opaque PKCS7/CMS Signature

See more Digital Signatures Examples

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. PureBasic

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

Procedure ChilkatExample()

    success.i = 0

    ; 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 = 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