(Go) 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 Go Downloads Go Package for Windows, MacOS, Linux, Alpine Linux, Solaris

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

    crypt := chilkat.NewCrypt2()

    // 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 := chilkat.NewCert()

    // If the smartcard or token requires a PIN, we can set it here to avoid the dialog...
    cert.SetSmartCardPin("000000")

    success := cert.LoadFromSmartcard("")
    if success != true {
        fmt.Println(cert.LastErrorText())
        crypt.DisposeCrypt2()
        cert.DisposeCert()
        return
    }

    // Tell it to use the cert and private key we've loaded.
    success = crypt.SetSigningCert(cert)
    if success != true {
        fmt.Println(crypt.LastErrorText())
        crypt.DisposeCrypt2()
        cert.DisposeCert()
        return
    }

    // Indicate we want the opaque signature in base64 format:
    crypt.SetEncodingMode("base64")

    // Sign the string using the "utf-8" byte representation:
    crypt.SetCharset("utf-8")

    // Create the opaque signature:
    originalData := "This is the string to be signed."
    opaqueSig := crypt.OpaqueSignStringENC(originalData)
    if crypt.LastMethodSuccess() != true {
        fmt.Println(crypt.LastErrorText())
        crypt.DisposeCrypt2()
        cert.DisposeCert()
        return
    }

    fmt.Println(*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 := chilkat.NewCrypt2()

    // 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 = vCrypt.SetVerifyCert(cert)
    if success != true {
        fmt.Println(vCrypt.LastErrorText())
        crypt.DisposeCrypt2()
        cert.DisposeCert()
        vCrypt.DisposeCrypt2()
        return
    }

    vCrypt.SetEncodingMode("base64")
    vCrypt.SetCharset("utf-8")

    extractedData := vCrypt.OpaqueVerifyStringENC(*opaqueSig)
    if vCrypt.LastMethodSuccess() != true {
        fmt.Println(vCrypt.LastErrorText())
        crypt.DisposeCrypt2()
        cert.DisposeCert()
        vCrypt.DisposeCrypt2()
        return
    }

    fmt.Println("The extracted data: ", *extractedData)

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

    crypt.DisposeCrypt2()
    cert.DisposeCert()
    vCrypt.DisposeCrypt2()