Man-in-the-Middle Attacks

Another English-Italian translation of a post taken from Bruce Schneier ‘s blog: Schneier on Security

Here is the source text:

Last week’s dramatic rescue of 15 hostages held by the guerrilla organization FARC was the result of months of intricate deception on the part of the Colombian government. At the center was a classic man-in-the-middle attack.

In a man-in-the-middle attack, the attacker inserts himself between two communicating parties. Both believe they’re talking to each other, and the attacker can delete or modify the communications at will.

The Wall Street Journal reported how this gambit played out in Colombia:

“The plan had a chance of working because, for months, in an operation one army officer likened to a ‘broken telephone,’ military intelligence had been able to convince Ms. Betancourt’s captor, Gerardo Aguilar, a guerrilla known as ‘Cesar,’ that he was communicating with his top bosses in the guerrillas’ seven-man secretariat. Army intelligence convinced top guerrilla leaders that they were talking to Cesar. In reality, both were talking to army intelligence.”

This ploy worked because Cesar and his guerrilla bosses didn’t know one another well. They didn’t recognize one anothers’ voices, and didn’t have a friendship or shared history that could have tipped them off about the ruse. Man-in-the-middle is defeated by context, and the FARC guerrillas didn’t have any.

And that’s why man-in-the-middle, abbreviated MITM in the computer-security community, is such a problem online: Internet communication is often stripped of any context. There’s no way to recognize someone’s face. There’s no way to recognize someone’s voice. When you receive an e-mail purporting to come from a person or organization, you have no idea who actually sent it. When you visit a website, you have no idea if you’re really visiting that website. We all like to pretend that we know who we’re communicating with — and for the most part, of course, there isn’t any attacker inserting himself into our communications — but in reality, we don’t. And there are lots of hacker tools that exploit this unjustified trust, and implement MITM attacks.

Even with context, it’s still possible for MITM to fool both sides — because electronic communications are often intermittent. Imagine that one of the FARC guerrillas became suspicious about who he was talking to. So he asks a question about their shared history as a test: “What did we have for dinner that time last year?” or something like that. On the telephone, the attacker wouldn’t be able to answer quickly, so his ruse would be discovered. But e-mail conversation isn’t synchronous. The attacker could simply pass that question through to the other end of the communications, and when he got the answer back, he would be able to reply.

This is the way MITM attacks work against web-based financial systems. A bank demands authentication from the user: a password, a one-time code from a token or whatever. The attacker sitting in the middle receives the request from the bank and passes it to the user. The user responds to the attacker, who passes that response to the bank. Now the bank assumes it is talking to the legitimate user, and the attacker is free to send transactions directly to the bank. This kind of attack completely bypasses any two-factor authentication mechanisms, and is becoming a more popular identity-theft tactic.

There are cryptographic solutions to MITM attacks, and there are secure web protocols that implement them. Many of them require shared secrets, though, making them useful only in situations where people already know and trust one another.

The NSA-designed STU-III and STE secure telephones solve the MITM problem by embedding the identity of each phone together with its key. (The NSA creates all keys and is trusted by everyone, so this works.) When two phones talk to each other securely, they exchange keys and display the other phone’s identity on a screen. Because the phone is in a secure location, the user now knows who he is talking to, and if the phone displays another organization — as it would if there were a MITM attack in progress — he should hang up.

Zfone, a secure VoIP system, protects against MITM attacks with a short authentication string. After two Zfone terminals exchange keys, both computers display a four-character string. The users are supposed to manually verify that both strings are the same — “my screen says 5C19; what does yours say?” — to ensure that the phones are communicating directly with each other and not with an MITM. The AT&T TSD-3600 worked similarly.

This sort of protection is embedded in SSL, although no one uses it. As it is normally used, SSL provides an encrypted communications link to whoever is at the other end: bank and phishing site alike. And the better phishing sites create valid SSL connections, so as to more effectively fool users. But if the user wanted to, he could manually check the SSL certificate to see if it was issued to “National Bank of Trustworthiness” or “Two Guys With a Computer in Nigeria.”

No one does, though, because you have to both remember and be willing to do the work. (The browsers could make this easier if they wanted to, but they don’t seem to want to.) In the real world, you can easily tell a branch of your bank from a money changer on a street corner. But on the internet, a phishing site can be easily made to look like your bank’s legitimate website. Any method of telling the two apart takes work. And that’s the first step to fooling you with a MITM attack.

Man-in-the-middle isn’t new, and it doesn’t have to be technological. But the internet makes the attacks easier and more powerful, and that’s not going to change anytime soon.

This essay originally appeared on Wired.com.


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Chinese Cyber Attacks

Here is the original post (the source text of my translation):

The popular media conception is that there is a coordinated attempt by the Chinese government to hack into U.S. computers — military, government corporate — and steal secrets. The truth is a lot more complicated.

There certainly is a lot of hacking coming out of China. Any company that does security monitoring sees it all the time.

These hacker groups seem not to be working for the Chinese government. They don’t seem to be coordinated by the Chinese military. They’re basically young, male, patriotic Chinese citizens, trying to demonstrate that they’re just as good as everyone else. As well as the American networks the media likes to talk about, their targets also include pro-Tibet, pro-Taiwan, Falun Gong and pro-Uyghur sites.

The hackers are in this for two reasons: fame and glory, and an attempt to make a living. The fame and glory comes from their nationalistic goals. Some of these hackers are heroes in China. They’re upholding the country’s honor against both anti-Chinese forces like the pro-Tibet movement and larger forces like the United States.

And the money comes from several sources. The groups sell owned computers, malware services, and data they steal on the black market. They sell hacker tools and videos to others wanting to play. They even sell T-shirts, hats and other merchandise on their Web sites.

This is not to say that the Chinese military ignores the hacker groups within their country. Certainly the Chinese government knows the leaders of the hacker movement and chooses to look the other way. They probably buy stolen intelligence from these hackers. They probably recruit for their own organizations from this self-selecting pool of experienced hacking experts. They certainly learn from the hackers.

And some of the hackers are good. Over the years, they have become more sophisticated in both tools and techniques. They’re stealthy. They do good network reconnaissance. My guess is what the Pentagon thinks is the problem is only a small percentage of the actual problem.

And they discover their own vulnerabilities. Earlier this year, one security company noticed a unique attack against a pro-Tibet organization. That same attack was also used two weeks earlier against a large multinational defense contractor.

They also hoard vulnerabilities. During the 1999 conflict over the two-states theory conflict, in a heated exchange with a group of Taiwanese hackers, one Chinese group threatened to unleash multiple stockpiled worms at once. There was no reason to disbelieve this threat.

If anything, the fact that these groups aren’t being run by the Chinese government makes the problem worse. Without central political coordination, they’re likely to take more risks, do more stupid things and generally ignore the political fallout of their actions.

In this regard, they’re more like a non-state actor.

So while I’m perfectly happy that the U.S. government is using the threat of Chinese hacking as an impetus to get their own cybersecurity in order, and I hope they succeed, I also hope that the U.S. government recognizes that these groups are not acting under the direction of the Chinese military and doesn’t treat their actions as officially approved by the Chinese government.

This essay originally appeared on the Discovery Channel website.


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