(Swift 3,4,5...) RSASSA-PSS Sign String to Create Base64 PCKS7 Signature

Signs a string to create a PKCS7 signature in the base64 encoding. The signature algorithm is RSASSA-PSS with SHA256.

Note: This example requires Chilkat v9.5.0.67 or greater.

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

    let crypt = CkoCrypt2()!

    // Get a digital certificate with private key from a .pfx
    // (Chilkat has many different ways to provide a cert + private key for siging.
    // Using a PFX is just one possible option.)
    let pfx = CkoPfx()!
    var success: Bool = pfx.loadFile("qa_data/rsassa-pss/privatekey.pfx", password: "PFX_PASSWORD")
    if success != true {
        print("\(pfx.lastErrorText!)")
        return
    }

    // Get the certificate to be used for signing.
    // (The typical case for a PFX is that it contains a cert with an associated private key,
    // as well as other certificates in the chain of authentication.  The cert with the private
    // key should be in the first position at index 0.)
    var cert: CkoCert? = pfx.getCert(0)
    if pfx.lastMethodSuccess != true {
        print("\(pfx.lastErrorText!)")
        return
    }

    crypt.setSigning(cert)

    // Indicate that RSASSA-PSS with SHA256 should be used.
    crypt.signingAlg = "pss"
    crypt.hashAlgorithm = "sha256"

    crypt.encodingMode = "base64"

    // Sign a string and return the base64 PKCS7 detached signature
    var originalText: String? = "This is a test"
    var pkcs7sig: String? = crypt.signStringENC(originalText)
    print("Detached Signature:")
    print("\(pkcs7sig!)")

    // This signature looks like this:
    // MIIG5wYJKoZIhvcNAQcCoIIG2DCCBtQCAQExDzANBgl .. YToLqEwTdU87ox5g7rvw==

    // The ASN.1 of the signature can be examined by browsing to https://lapo.it/asn1js/ ,
    // then copy-and-paste the Base64 signature into the form and decode..

    // The signature can be verified against the original data like this:
    success = crypt.verifyStringENC(originalText, encodedSig: pkcs7sig)
    print("Signature verified: \(success)")
    success = crypt.verifyStringENC("Not the original text", encodedSig: pkcs7sig)
    print("Signature verified: \(success)")

    // Now we'll create an opaque signature (the opposite of a detached signature). 
    // An opaque signature is a PKCS7 message that contains both the original data and
    // the signature.  The verification process extracts the original data.
    var opaqueSig: String? = crypt.opaqueSignStringENC(originalText)
    print("Opaque Signature:")
    print("\(opaqueSig!)")

    // The ASN.1 of the signature can be examined by browsing to https://lapo.it/asn1js/ ,
    // then copy-and-paste the Base64 signature into the form and decode..

    // We can verify and extract the original data:
    var origTxt: String? = crypt.opaqueVerifyStringENC(opaqueSig)
    if crypt.lastMethodSuccess != true {
        print("Signature verification failed.")
        print("\(crypt.lastErrorText!)")
        cert = nil
        return
    }

    print("Signature verified.")
    print("Extracted text:\(origTxt!)")

    cert = nil

}