From c2816d47cba24a88315732d41467913c6e93a70e Mon Sep 17 00:00:00 2001
From: Marcus Bointon <marcus@synchromedia.co.uk>
Date: Tue, 3 May 2016 10:06:15 +0200
Subject: [PATCH] Add DNS entry generator, fixes #644

---
 examples/DKIM_gen_keys.phps | 63 ++++++++++++++++++++++++++++---------
 1 file changed, 48 insertions(+), 15 deletions(-)

diff --git a/examples/DKIM_gen_keys.phps b/examples/DKIM_gen_keys.phps
index cf3f58b8..efd9197d 100644
--- a/examples/DKIM_gen_keys.phps
+++ b/examples/DKIM_gen_keys.phps
@@ -21,24 +21,57 @@
  * inserted there using the selector you want to use.
  */
 
+//Set these to match your domain and chosen DKIM selector
+$domain = 'example.com';
+$selector = 'phpmailer';
+
 //Path to your private key:
 $privatekeyfile = 'dkim_private.pem';
 //Path to your public key:
 $publickeyfile = 'dkim_public.pem';
 
-//Create a 2048-bit RSA key with an SHA256 digest
-$pk = openssl_pkey_new(
-    [
-        'digest_alg'       => 'sha256',
-        'private_key_bits' => 2048,
-        'private_key_type' => OPENSSL_KEYTYPE_RSA
-    ]
-);
-//Save private key
-openssl_pkey_export_to_file($pk, $privatekeyfile);
-//Save public key
-$pubKey = openssl_pkey_get_details($pk);
-file_put_contents($publickeyfile, $pubKey['key']);
+if (file_exists($privatekeyfile)) {
+    echo "Using existing keys - if you want to generate new keys, delete old key files first.\n\n";
+    $privatekey = file_get_contents($privatekeyfile);
+    $publickey = file_get_contents($publickeyfile);
+} else {
+    //Create a 2048-bit RSA key with an SHA256 digest
+    $pk = openssl_pkey_new(
+        [
+            'digest_alg' => 'sha256',
+            'private_key_bits' => 2048,
+            'private_key_type' => OPENSSL_KEYTYPE_RSA
+        ]
+    );
+    //Save private key
+    openssl_pkey_export_to_file($pk, $privatekeyfile);
+    //Save public key
+    $pubKey = openssl_pkey_get_details($pk);
+    $publickey = $pubKey['key'];
+    file_put_contents($publickeyfile, $publickey);
+    $privatekey = file_get_contents($privatekeyfile);
+}
+echo "Private key (keep this private!):\n\n" . $privatekey;
+echo "\n\nPublic key:\n\n" . $publickey;
 
-echo file_get_contents($privatekeyfile);
-echo $pubKey['key'];
+//Prep public key for DNS, e.g.
+//phpmailer._domainkey.example.com IN TXT "v=DKIM1; h=sha256; t=s; p=" "MIIBIjANBg...oXlwIDAQAB"...
+$dnskey = "$selector._domainkey.$domain IN TXT";
+//Some DNS server don't like ; chars unless backslash-escaped
+$dnsvalue = '"v=DKIM1\; h=sha256\; t=s\; p=" ';
+
+//Strip and split the key into smaller parts and format for DNS
+//Many DNS systems don't like long TXT entries
+//but are OK if it's split into 255-char chunks
+//Remove PEM wrapper
+$publickey = preg_replace('/^-+.*?-+$/m', '' , $publickey);
+//Strip line breaks
+$publickey = str_replace(["\r", "\n"], '', $publickey);
+//Split into chunks
+$keyparts = str_split($publickey, 253); //Becomes 255 when quotes are included
+//Quote each chunk
+foreach($keyparts as $keypart) {
+    $dnsvalue .= '"'.trim($keypart).'" ';
+}
+echo "\n\nDNS key:\n\n" . trim($dnskey);
+echo "\n\nDNS value:\n\n" . trim($dnsvalue);