When cryptography attacks – how TLS helps malware hide in plain sight

Security

Lots of things that we rely on, and that are generally regarded as bringing value, convenience and benefit to our lives…

…can be used for harm as well as good.

Even the proverbial double-edged sword, which theoretically gave ancient warriors twice as much fighting power by having twice as much attack surface, turned out to be, well, a double-edged sword.

With no “safe edge” at the rear, a double-edged sword that was mishandled, or driven back by an assailant’s counter-attack, became a direct threat to the person wielding it instead of to their opponent.

Sadly, there are lots of metaphorically double-edged swords amidst modern technology.

And no IT technology feels quite as double-edged as encryption, the process of scrambling data securely in such a way that only the intended recipient can ever unscramble it later on.

Almost everything about encryption makes it feel as though it is both immeasurably useful and dispiritingly dangerous at the same time.

The encryption dilemma

Consider some of these dilemmas:

  • You work out how to crack your enemy’s “invincible” cipher in wartime. (The Poles, Swedes, British and others famously and almost unbelievably pulled this off against several Nazi encryption systems during World War 2.) But you daren’t let anyone find out how well you’re doing, and you can’t even use all of the information you decrypt, in case the enemy cottons on and changes the system.
  • You encrypt all the critical data on your computer to protect it from thieves and hackers. But you’d better not lose the decryption key, or you won’t be able to access the information yourself. (Ironically, the stronger and safer the encryption technology you use, the less likely you’ll be able to crack it yourself if you ever forget the password.)
  • You implement an encryption system that gives you an advantage over the hackers who keep trying to attack you. But it’s so useful at keeping the hackers out of your business that the hackers start using exactly the same technology themelves, and suddenly you can’t keep track of their business, either.

This last dilemma is one that has been creeping up on us steadily over the last few years on the web.

TLS (transport layer security), the protocol used to encrypt the majority of today’s web and email traffic, is what puts the padlock in your browser’s address bar.

By doing so, TLS makes it very much harder for crooks to do three things:

  1. The crooks can’t easily snoop on the data you’re sending to a website, such as your login password or credit card number.
  2. They can’t easily tamper with the data that’s coming back, such as altering the bank balance to stop you noticing a fraud, or replacing an innocent download with dangerous malware.
  3. They can’t easily spoof you into thinking that their fraudulent, cloned website belongs to a brand or product you trust, such as your bank or a social network.

TLS takes off everywhere

Ten years ago, even the biggest and most popular online services in the world, such as Facebook, Gmail and Hotmail (now Outlook.com) didn’t use TLS all the time – it was thought to be too complicated, too slow, and not always necessary.

Sure, social media sites or online stores would encrypt the important stuff, such as when you actually logged in, or paid for something, or edited your private profile.

But the rest of the time, they’d often just use unencrypted web pages, figuring that you didn’t really needed protection against snooping, tampering and spoofing when you were “just looking”.

Well, that sort of simplification won’t wash any more, because we give away more than enough to put us in harm’s way just during regular browsing.

These days, therefore, we expect our web browsing to be protected by TLS all the time.

And most of the time these days, it is.

Everything looks the same

Guess what?

The crooks have fallen in love with TLS as well.

By using TLS to conceal their malware machinations inside an encrypted layer, cybercriminals can make it harder for us to figure out what they’re up to.

That’s because one stream of encrypted data looks much the same as any other.

Given a file that contains properly-encrypted data, you have no way of telling whether the original input was the complete text of the Holy Bible, or the compiled code of the world’s most dangerous ransomware.

After they’re encrypted, you simply can’t tell them apart – indeed, a well-designed encryption algorithm should convert any input plaintext into an output ciphertext that is indistinguishable from the sort of data you get by repeatedly rolling a die.

Paradoxically, then, as more and more of the internet gets encrypted, thus keeping us more secure…

…it also gets harder and harder to keep track of anomalous, unwanted and dangerous content.

When data is properly encrypted, you can’t differentiate between ciphertexts even if you know what the plaintexts were.

Keeping on top of it all

At this point, you’re probably wondering just exactly what the crooks are getting up to these days with TLS, and how much they’re using it.

And the excellent news is that Sean Gallagher of SophosLabs has just completed an extensive survey, based on data gathered from all around the world via our own software, to answer exactly those questions.

In his paper, published today, entitled Nearly half of malware now use TLS to conceal communications, he takes you through the tricks used by today’s cybercriminals to help them hide in plain sight, simply by making their bad traffic look much the same as our good traffic.

From just under a quarter of malware-related traffic using TLS a year ago to just under half today, this is definitely an issue you should be aware of.

As Sean writes:

The most concerning trend we’ve noted is the use of commercial cloud and web services as part of malware deployment, command and control. Malware authors’ abuse of legitimate communication platforms gives them the benefit of encrypted communications provided by Google Docs, Discord, Telegram, Pastebin and others—and, in some cases, they also benefit from the “safe” reputation of those platforms.

We also see the use of off-the-shelf offensive security tools and other ready-made tools and application programming interfaces that make using TLS-based communications more accessible continuing to grow.

Learn how these attacks work, and how SophosLabs is able to keep on top of them even though they’re encrypted.


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