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SSLv3 no longer supported

10/22/2014

I had SSLv3 disabled for HTTP for quite some time. In the light of recent event, it is now also disabled for IMAP and SMTP. If you run into any trouble, let us know or update your clients.

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Case study: Howard Johnson Hotel – how NOT to sell your Wifi

11/24/2013

nessus-1Few things are more annoying than hotels, who think they need to earn some extra cash by charging people for wireless internet. Given the low to nonexistent cost of providing the service, they should also charge for warm water or fresh air, when following the same logic.

In the case of a local Howard-Johnson (HoJo) hotel, the wifi’s paywall was so badly implemented, it actually posed a threat to the rest of the hotel. Below, I will describe 4 options, anyone can use to get free internet at this particular hotel. Read the rest of this post »

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Setting Postfix to encrypt all traffic when talking to other mailservers

07/7/2013

Update Aug 9, 2013: The biggest German email providers are currently running a big marketing campaign and promise secure email. They are using the same technique described on this page. After checking my logs, I can confirm that GMX-emails were delivered unencrypted on Aug 5, but arrived encrypted on Aug 6.

Thanks to Mr. Snowden, we know two important facts about the world of security and email:

First, most governments in the world will eavesdrop and store your communication, if they get the chance. They don’t have a specific reason and the benefits are highly disputed.

Second, your users can’t/won’t use PGP or S/MIME to encrypt their email.

The job is left to admins. We need to maximize usability and compatibility, while ensuring that user data stays confidential. If you are running Postfix, I’d like to draw your attention to some useful settings that will protect your user’s email in transit. If emails stay on the same server or the other server is secured as well, there is little chance to intercept messages on a big scale. If your users are sending emails to Gmail or Hotmail, then interception is still possible at the receiving end.

Make Postfix encrypt messages at all stages of delivery.

Figure 1: Vulnerability of email-messages in transit.

Read the rest of this post »

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UPC Vienna Wifi-Passwords easily broken with GPUs

06/10/2012

With a majority of households using wireless access points (AP) for internet, secure Wifi has become a key consideration in people’s digital lifes. The outdated encryption standard WEP, which is rarely used any more can be broken in less than 10 minutes. For the newer WPA no direct attack exists so far. The only way is to try a large number of passwords.

Recent advances in parallel computing and graphic cards (GPU) have drastically shifted the odds in favour of potential attackers. With an ordinary CPU, found in most desktop computers and laptops, about 500 Pairwise Master Key (PMK) can be evaluated each second. Modern GPUs can calculate up to 80 000 PMKs per second.

Such an increase in speed doesn’t mean that each and every wireless network is at risk, it only shifts the vulnerable keylength further up. Consider this: At 500 PMKs per second it would take approximately 3 years to break a 6-digit password that uses upper- and lower letters, as well as digits. When using a high-end GPU, 3 years become 5.5 days.

Since password complexity increases in an exponential fashion, slightly longer passwords offer a radically better protection. A 8-letter password from the same number space would take 50 years to crack, even on a high-end GPU.

As we can see, faster cracking techniques only affect password length at the margin, if done right. At UPC Vienna, in Austria this principle is not as well understood. The routers that come bundeld with their broadband connection use an 8-letter password that only seems to consist of capital letters. (I only have access to a limited sample at this time.)

When doing the same calculations as before, such a password took about 7 years to crack, when done on a standard CPU. This would be a huge effort, just to steal your neighbors internet. If we throm in GPUs, the story changes. 7 years become about 16 days on a single workstation. This timespan is quite doable. When performing the calculations in Amazon’s EC2 cloud each UPC-password can be cracked at the cost of about 180 EUR in 3-4 hours. This number is expeced to come down in the following months, due to an increased interest in the topic.

Since it’s not feasible for UPC to change hundreds of thousands of passwords in Vienna (and maybe the whole of Austria), consumers need to act for themselves and pick a more secure key for their AP.

 

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Secure backups in an untrusted cloud with duplicity

01/29/2012

These days it’s quite easy to get incredible deals on shared hosting space. Mostly with dodgy providers in the US or former cyberlockers (like filesonic). They don’t give you SSH access, but only FTP. Rsync doesn’t work with FTP, but duplicity does. While not as robust and fast as rsync, it’s built to work with any service that can store files. Examples include any FTP-server, Amazon S3 and SFTP.

Many tutorials suggest using a GnuPG-key for asymetric encryption, but for only protecting your content from the hosting provider, a simple symetric password should work just as well and makes things easier. So a simple working example would be:

export PASSPHRASE=xxx
export FTP_PASSWORD=xxx
export SOURCE=$HOME
export TARGET=ftp://foo@bar.com/backups/machine

duplicity -v8 \
--exclude $HOME/'Library/Logs' \
--exclude-regexp '\.DS_Store' \
--exclude-regexp '^~\$.*' \
$SOURCE $TARGET

This works well on both Linux and Mac OSX machines. Extended options can be found on the duplicity man pages.

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