(Swift 3,4,5...) Verify DKIM-Signature Headers in Downloaded Email

Downloads email from an IMAP server and verifies the DKIM-Signature header(s) in each email, if present.

Chilkat Downloads for the Swift Programming Language MAC OS X (Cocoa) Objective-C/Swift Libs iOS Objective-C/Swift Libs

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

    let imap = CkoImap()!

    // Connect to an IMAP server, login, select mailbox..
    // Use TLS 
    imap.ssl = true
    imap.port = 993
    var success: Bool = imap.connect("imap.someMailServer.com")
    if success == true {
        success = imap.login("myLogin", password: "myPassword")
        if success == true {
            success = imap.selectMailbox("Inbox")
        }

    }

    if success != true {
        print("\(imap.lastErrorText!)")
        return
    }

    let dkim = CkoDkim()!

    // Download a max of 10 emails and verify any DKIM-Signature headers
    // that are present.

    // Download emails by sequence numbers (not UIDs).
    var bUid: Bool = false
    var seqNum: Int
    var j: Int
    var n: Int = imap.numMessages.intValue
    if n > 10 {
        n = 10
    }

    let json = CkoJsonObject()!
    json.emitCompact = false

    // To verify DKIM-Signature headers, we need the exact unmodified MIME bytes of each email.
    let mimeData = CkoBinData()!
    seqNum = 1
    while seqNum <= n {
        // The FetchSingleBd method was introduced in v9.5.0.76
        success = imap.fetchSingleBd(seqNum, bUid: bUid, mimeData: mimeData)
        if success != true {
            print("\(imap.lastErrorText!)")
            return
        }

        // Get the number of DKIM-Signature headers.
        var numDkim: Int = dkim.numSigs(mimeData).intValue

        // Verify each..
        j = 0
        while j < numDkim {
            print("------ DKIM Signature \(j)")

            success = dkim.dkimVerify(j, mimeData: mimeData)
            if success != true {
                print("Not valid.")
            }
            else {
                print("valid.")
            }

            // Show the additional information about the signature verification
            json.load(dkim.verifyInfo)
            print("\(json.emit()!)")

            // The JSON contains information such as this:

            // 	{
            // 	  "domain": "amazonses.com",
            // 	  "selector": "7v7vs6w47njt4pimodk5mmttbegzsi6n",
            // 	  "publicKey": "MIGfMA0GCSqG...v2GvWPqGHz6uqeQIDAQAB",
            // 	  "canonicalization": "relaxed/simple",
            // 	  "algorithm": "rsa-sha256",
            // 	  "signedHeaders": "Subject:From:To:Date:Mime-Version:Content-Type:References:Message-Id:Feedback-ID",
            // 	  "verified": "yes"
            // 	}

            j = j + 1
        }

        seqNum = seqNum + 1
    }

    success = imap.disconnect()

}