Mandatory TLS is coming

Well, not exactly mandatory but Chrome will start labeling any text or email form field on a non-TLS page as “NOT SECURE”.

Chrome 62 will be released as stable some time around October 24th. If you want to avoid the customer support overhead then, regardless of whether any of the information on a form is sensitive, you should probably make sure that all your forms are accessible via TLS and redirect any attempt to access them over plain http to https. You can do that globally for a whole site pretty easily, and there’s not really any downside to doing so.
I still have half a dozen sites I need to convert to supporting TLS – the cobbler’s children have no shoes – and I’m beginning to feel a little urgency about it.
There’s more information in Google’s announcement, their checklist of how to set up TLS, and some background at Kaspersky Labs.

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Google drops obsolete crypto

Google is disabling support for email sent using version 3 of SSL or using the RC4 cypher.
They’re both very old – SSLv3 was obsoleted by TLS1.0 in 1999, and RC4 is nearly thirty years old and while it’s aged better than some cyphers there are multiple attacks against it and it’s been replaced with more recent cyphers almost everywhere.
Google has more to say about it on their security blog and if you’re developing software you should definitely pay attention to the requirements there: TLS1.2, SNI, TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256, DNS alternate names with wildcards.
For everyone else, make sure that you’ve applied any patches your vendor has available well before the cutoff date of June 16th.

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Cryptography and Email

A decade or so ago it was fairly rare for cryptography and email technology to intersect – there was S/MIME (which I’ve seen described as having “more implementations than users”) and PGP, which was mostly known for adding inscrutable blocks of text to mail and for some interesting political fallout, but not much else.
pgp
That’s changing, though. Authentication and privacy have been the focus of much of the development around email for the past few years, and cryptography, specifically public-key cryptography, is the tool of choice.
DKIM uses public-key cryptography to let the author (or their ESP, or anyone else) attach their identity to the message in a way that’s almost impossible to forge. That lets the recipient make informed decisions about whether to deliver the email or not.
DKIM relies on DNS to distribute it’s public keys, so if you can interfere with DNS, you can compromise DKIM. More than that, if you can compromise DNS you can break many security processes – interfering with DNS is an early part of many attacks. DNSSEC (Domain Name System Security Extensions) lets you be more confident that the results you get back from a DNS query are valid. It’s all based on public-key cryptography. It’s taken a long time to deploy, but is gaining steam.
TLS has escaped from the web, and is used in several places in email. For end users it protects their email (and their passwords) as they send mail via their smarthost or fetch it from their IMAP server. More recently, though, it’s begun to be used “opportunistically” to protect mail as it travels between servers – more than half of the mail gmail sees is protected in transit. Again, public-key cryptography. Perhaps you don’t care about the privacy of the mail you’re sending, but the recipient ISP may. Google already give better search ranking for web pages served over TLS – I wouldn’t be surprised if they started to give preferential treatment to email delivered via TLS.
The IETF is beginning to discuss end-to-end encryption of mail, to protect mail against interception and traffic analysis. I’m not sure exactly where it’s going to end up, but I’m sure the end product will be cobbled together using, yes, public-key cryptography. There are existing approaches that work, such as S/MIME and PGP, but they’re fairly user-hostile. Attempts to package them in a more user-friendly manner have mostly failed so far, sometimes spectacularly. (Hushmail sacrificed end-to-end security for user convenience, while Lavabit had similar problems and poor legal advice).
Not directly email-related, but after the flurry of ESP client account breaches a lot of people got very interested in two-factor authentication for their users. TOTP (Time-Based One-Time Passwords) – as implemented by SecureID and Google Authenticator, amongst many others – is the most commonly used method. It’s based on public-key cryptography. (And it’s reasonably easy to integrate into services you offer).
Lots of the other internet infrastructure you’re relying on (BGP, syn cookies, VPNs, IPsec, https, anything where the manual mentions “certificate” or “key” …) rely on cryptography to work reliably. Knowing a little about how cryptography works can help you understand all of this infrastructure and avoid problems with it. If you’re already a cryptography ninja none of this will be a surprise – but if you’re not, I’m going to try and explain some of the concepts tomorrow.

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Protocol-relative URLs in email

When you link to an external resource – an image, a javascript file, some css style – from a web page you do so with a URL, usually something like “https://example.com/blahblah.css” or “http://example.com/blahblah.css”.
The world is beginning to go all https, all the time, but until recently good practice was to make a web page available via both http and https.
The problem is that if you try and load a resource from an http URL from a page that was loaded via https it’ll complain about it, and not load the resource.
And if your users web browser is loading the http version of your page because it’s Internet Explorer 6 and doesn’t speak modern SSL then it’ll be unable to load anything over https, including any of your resources.
So whether you choose https or http protocol for loading your page resources it’s going to break for someone.
One common trick to avoid the problem is to use a protocol-relative URL. That looks like “//example.com/blahblah.css”, and it’ll load the resource over the same protocol that the page was loaded over.
While we can safely use “https://…” everywhere now, “//…” URLs are still a common idiom for things like loading things like CSS libraries from public content-distribution networks as well as your own resources.
I was reading long-but-excellent writeup about Stack Overflow’s migration to TLS (hey, I read this sort of stuff for fun) and they point out something I hadn’t considered – mail clients don’t really have any sensible way to use protocol-relative URLs. The mail client loaded the “page” from a mailbox and so has no base document protocol to work from (even if there’s a <base> element in the content it’s not likely to affect a mail client). If the user is reading it via webmail or a mail client that’s using an embedded web browser to render HTML it might work, sometimes, but it’s not going to reliably load that resource in general.
So, if you’re copy-pasting content from your web collateral to reuse in an email, make sure you’re not loading anything external – including images – via a “//…” style URL. Rewrite them to use “https://…”.
 

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