(Swift 3,4,5...) Decrypt S/MIME and Verify S/MIME Signatures

Swift 3,4,5... example to decrypt S/MIME and verify S/MIME signatures. The S/MIME is unwrapped to get the original MIME prior to signing/encrypting.

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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 mime = CkoMime()!

    // Load an S/MIME message from a file:
    var success: Bool = mime.loadFile("signedMime.txt")
    if success != true {
        print("\(mime.lastErrorText!)")
        return
    }

    // The ContainsEncryptedParts/ContainsSignedParts methods
    // can be called to determine if the MIME is encrypted and/or signed:
    var isEncrypted: Bool = mime.containsEncryptedParts()
    var isSigned: Bool = mime.containsSignedParts()

    // We don't want the "unwrap extras".  You'll see what those
    // are in a few moments...
    mime.unwrapExtras = false

    // To verify the signature, call UnwrapSecurity.  This will
    // verify the signature(s) and decrypt the S/MIME and restore
    // the MIME to the unsigned/unencrypted state.
    // The results of what was found are present in the MIME object's
    // properties, as well as extra header fields that are added
    // to the unwrapped MIME.
    success = mime.unwrapSecurity()
    if success != true {
        // UnwrapSecurity returns true if all signatures were
        // verified and all parts decrypted.
        print("\(mime.lastErrorText!)")
        return
    }

    // The mime.UnwrapExtras property controls whether or not
    // these additional fields are added to the unwrapped MIME:
    // 
    // X-NumPartsSigned: 1
    // X-SignaturesValid: yes
    // X-NumPartsEncrypted: 1
    // X-Decrypted: no
    // 
    // The X-NumPartsSigned/X-SignaturesValid headers are added
    // if the MIME was signed.  
    // 
    // The X-NumPartsEncrypted/X-Decrypted headers are added
    // if the MIME was encrypted.
    // 

    // If the MIME was signed, get the certificate used for signing.
    if isSigned == true {
        // The NumSignerCerts property indicates how many certificates
        // were used for signing.  This example will assume the value is 1.
        // To get the 1st signer cert, call GetSignerCert with an index of 0:
        var signerCert: CkoCert? = mime.getSignerCert(0)
        if mime.lastMethodSuccess == true {
            print("**** Signer Cert: \(signerCert!.subjectCN!)")
            signerCert = nil
        }

    }

    // If the MIME was encrypted, get the certificate used for encryption:
    if isEncrypted == true {
        // The NumEncryptCerts property indicates how many certificates
        // were used for encrypting.  This example will assume the value is 1.
        // To get the 1st encrypt cert, call GetEncryptCert with an index of 0:
        var encryptCert: CkoCert? = mime.getEncryptCert(0)
        if mime.lastMethodSuccess == true {
            print("**** Encrypt Cert: \(encryptCert!.subjectCN!)")
            encryptCert = nil
        }

    }

    // Display the unwrapped MIME:
    print("\(mime.getMime()!)")

    // Save the unwrapped MIME to a file:
    success = mime.save("unwrappedMime.txt")

}