(Swift 3,4,5...) Sign PDF: Choosing RSASSA-PSS or PKCS1-v1_5 and Hash Algorithm

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This example demonstrates how to choose between RSASSA-PSS vs. PKCS1-v1_5 and the hash algorithm when signing a PDF.

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func chilkatTest() {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    let pdf = CkoPdf()!

    // Load a PDF to be signed.
    // The "hello.pdf" is available at https://chilkatsoft.com/hello.pdf
    var success: Bool = pdf.loadFile("qa_data/pdf/hello.pdf")
    if success == false {
        print("\(pdf.lastErrorText!)")
        return
    }

    // Options for signing are specified in JSON.
    let json = CkoJsonObject()!

    // In most cases, the signingCertificateV2 attribute is needed.
    json.updateInt("signingCertificateV2", value: 1)

    // ---------------------------------------------------------------------------------------------------------------------------
    // This example is the same as the example at Sign a PDF (Simplest Example Possible)
    // but with the following lines added to specify the signature scheme and hash algorithm.

    // The signature schemes PKCS-v1_5 and RSASSA-PSS have differences. 
    // PKCSV1_5 is deterministic. The same message and key will produce an identical signature value each time. 
    // PSS is randomized and will produce a different signature value each time.

    // To choose the hash algorithm:
    // (The typical choices are sha1, sha256, sha384, and sha512.)
    json.update("hashAlgorithm", value: "sha256")

    // To choose PKCSV1_5:
    json.update("signingAlgorithm", value: "pkcs")
    // Alternatively, to choose RSASSA-PSS:
    json.update("signingAlgorithm", value: "pss")

    // If not specified, the default is SHA256 with PKCS-v1_5.

    // The remainder of this example is the same as the example at Sign a PDF (Simplest Example Possible)
    // ---------------------------------------------------------------------------------------------------------------------------

    // Put the signature on page 1, top left
    json.updateInt("page", value: 1)
    json.update("appearance.y", value: "top")
    json.update("appearance.x", value: "left")

    // Use a font scale of 10.0
    json.update("appearance.fontScale", value: "10.0")

    // In this example, the appearance of the digital signature will contain three lines:
    // 1) The signing certificate's common name
    // 2) The current date/time
    // 3) Some arbitrary text.
    // The keyword "cert_cn" is replaced with the Certificate's Subject Common Name.
    // The keyword "current_dt" is replaced with the current date/time.
    // Any number of appearance text lines can be added.
    json.update("appearance.text[0]", value: "Digitally signed by: cert_cn")
    json.update("appearance.text[1]", value: "current_dt")
    json.update("appearance.text[2]", value: "The crazy brown fox jumps over the lazy dog.")

    // Load the signing certificate. (Use your own certificate.)
    let cert = CkoCert()!
    success = cert.loadPfxFile("qa_data/pfx/myPdfSigningCert.pfx", password: "secret")
    if success == false {
        print("\(cert.lastErrorText!)")
        return
    }

    // Tell the pdf object to use the certificate for signing.
    success = pdf.setSigning(cert)
    if success == false {
        print("\(pdf.lastErrorText!)")
        return
    }

    success = pdf.sign(json, outFilePath: "qa_output/hello_signed.pdf")
    if success == false {
        print("\(pdf.lastErrorText!)")
        return
    }

    print("The PDF has been successfully cryptographically signed.")

    // The appearance of the signature appears in Adobe Acrobat as shown here:

    

}