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MEGApwn - Bookmarklet to recover your secret MEGA master key

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Re: MEGApwn - Bookmarklet to recover your secret MEGA master key

#11

Post by nly »

traskjd wrote: post #9
nly wrote: post #8

Earlier quoted context omitted.

This didn't need proving. They send you JavaScript code, which you trust to encrypt your files. Without a built-in, well-audited, static browser mechanism no web service can ever be trusted with confidential data . If the Feds decide to raid MEGA again they can simply modify their server side script to recognise your IP and serve you bad JavaScript from the MEGA domain, revealing your keys the next time you login. No…

Sure, but don't you think it's important that they make this clear? So far they market heavily on the fact that it's secure when this is simply not true. If you read their security page, they do say you shouldn't use it if you don't trust them. But that's about it for any warning that you're basically sitting there naked. I know no security system is entirely secure, but they aren't generally targeting security minde…

Meh. Should every site using HTTPS make it clear that hundreds of CAs whom you've never heard of have the capability to perform a MITM?

At least with MEGA you know the security framework is something they've engineered themselves, so you know you have to trust them. With SSL/TLS you're deferring to authority simply because it's convenient.

Re: MEGApwn - Bookmarklet to recover your secret MEGA master key

#12

Post by nly »

nhm wrote: post #10
nly wrote: post #8

Earlier quoted context omitted.

This didn't need proving. They send you JavaScript code, which you trust to encrypt your files. Without a built-in, well-audited, static browser mechanism no web service can ever be trusted with confidential data . If the Feds decide to raid MEGA again they can simply modify their server side script to recognise your IP and serve you bad JavaScript from the MEGA domain, revealing your keys the next time you login. No…

The article isn't proving anything, it's an example of how a known problem affects MEGA. It's saying encrypt your files first, because trusting MEGA (or anyone who uses that kind of encryption) is not enough.

You're right, this just highlights the nature of the site in a very effective way. The message here is nobody should be surprised.

Re: MEGApwn - Bookmarklet to recover your secret MEGA master key

#13

Post by revelation »

This isn't even exactly about JavaScript cryptography. This is the equivalent to building a program to read the TrueCrypt keys out of memory.

The problem here is "the machine doing the cryptography can not be trusted", not "it's JavaScript in a webbrowser", though of course thats also a fundamental problem.

Re: MEGApwn - Bookmarklet to recover your secret MEGA master key

#14

Post by doublec »

traskjd wrote: post #6
doublec wrote: post #4

This JS code needs to be run on the MEGA domain, right? That's why it's a bookmarklet. Other sites don't have access to the local storage required to extract the key. It does mean that MEGA can get the key and send it back to the site if MEGA was compromised but ultimately the client code needs to get the key to decrypt the MEGA content. Some way of pinning or signing JavaScript verified by a third party or browser w…

Isn't the issue more that Mega portray that they CAN'T see what files you're storing (plausible deniability regarding pirated content) while this proves that they actually could see your file contents if they wanted to? Which in turn really means it's no more secure than, say, DropBox. At least that's the impression I have regarding why this is somewhat important.

It's more secure than DropBox in that someone seizing MEGA's data can't read it. A MEGA employee can't read your data. To read your data they need to capture the private key. This is possible by virtue of the fact that they're sending you the code to use the private key.

Re: MEGApwn - Bookmarklet to recover your secret MEGA master key

#16

Post by biot »

The issue here is that MEGA presents itself as "the privacy company" and makes some very careful claims about encryption:

  All files stored on MEGA are encrypted. All data transfers from and
  to MEGA are encrypted. And while most cloud storage providers can
  and do claim the same, MEGA is different – unlike the industry norm
  where the cloud storage provider holds the decryption key, with
  MEGA, you control the encryption, you hold the keys, and you decide
  who you grant or deny access to your files, without requiring any
  risky software installs. It’s all happening in your web browser!
It's true that everything is encrypted. And it's true that many cloud storage providers hold the decryption keys. It's also true that with MEGA, you hold the keys. What they carefully avoid claiming is that MEGA is unable to read the decryption keys.

All it takes is one court order in a country where MEGA operates ordering them to obtain the user-held decryption keys via the exact same method this bookmarklet demonstrates. MEGA doesn't even have to be involved. In the US, a National Security Letter to your ISP could lead to a man-in-the-middle attack with the help of an SSL certificate that the government orders a trusted CA to provide for MEGA's domain. At that point, all of MEGA's carefully-crafted claims about security are moot.

Re: MEGApwn - Bookmarklet to recover your secret MEGA master key

#17

Post by snissn »

They could AES your keys before storing it in local storage and prompt the user for this extra key whenever they need to access your keys. Otherwise your private keys are just stored in a sqlite file or some other implementation specific file that your browser created on your file system.

Re: MEGApwn - Bookmarklet to recover your secret MEGA master key

#18

Post by pyre »

biot wrote: post #16

The issue here is that MEGA presents itself as "the privacy company" and makes some very careful claims about encryption: All files stored on MEGA are encrypted. All data transfers from and to MEGA are encrypted. And while most cloud storage providers can and do claim the same, MEGA is different – unlike the industry norm where the cloud storage provider holds the decryption key, with MEGA, you control the encryption…

If the government has compromised trusted CAs to do man-in-the-middle attacks, my thought is that they are only for 'intelligence' levels of actions, at least at this point in time. The government isn't going to tip its hand to foreign adversaries even to jail a few pedophiles (or other breakers of Federal law).

Re: MEGApwn - Bookmarklet to recover your secret MEGA master key

#20

Post by [deleted] »

traskjd wrote: post #6
doublec wrote: post #4

This JS code needs to be run on the MEGA domain, right? That's why it's a bookmarklet. Other sites don't have access to the local storage required to extract the key. It does mean that MEGA can get the key and send it back to the site if MEGA was compromised but ultimately the client code needs to get the key to decrypt the MEGA content. Some way of pinning or signing JavaScript verified by a third party or browser w…

Isn't the issue more that Mega portray that they CAN'T see what files you're storing (plausible deniability regarding pirated content) while this proves that they actually could see your file contents if they wanted to? Which in turn really means it's no more secure than, say, DropBox. At least that's the impression I have regarding why this is somewhat important.

[deleted]
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