Monthly Archives: May 2014

Development, Electronics, Mozilla

Crashed and recovered in no time

Working from home, even writing software from home, my computer setup is pretty crucial for a productive work day.

Yesterday morning after I had sat down with my coffee and started to work on my latest patch iteration I noticed that some disk operations seemed to be very slow. I looked around and then suddenly an ‘ls’ of a directory returned an error!

I checked the system logs and I saw them filling up with error messages identifying problems with a hard drive. Very quickly I identified the drive as the bigger one (I have one SSD and one much larger HDD). Luckily, that’s the one I mostly store document, pictures and videos on and I backup that thing every night. This disk is not very old and I’ve never experienced this sort of disk crash before, not even with disks that I’ve used for many years more than I’ve used this…

boomI ripped the thing out, booted up again and I could still work since my source code and OS are on the SSD. I ordered a new one at once. Phew.

Tuesday morning I noticed that for some unexplainable reason I had my /var partition on the dead drive (and not backed up). That turned out to be a bit inconvenient since now my Debian Linux had no idea which packages I had installed and apt-get and dpkg were all crippled to death.

I did some googling and as my laptop is also a Debian sid install I managed to restore it pretty swiftly by copying over data from there. At least it (the /var contents) is now mostly back to where it was before.

On Tuesday midday, some 26 hours after I ripped out the disk, my doorbell bing-bonged and the delivery guy handed me a box with a new and shiny 3 TB drive. A couple of hours ago I inserted it, portioned it, read back a couple of hundred gigabytes of backup, put back the backup job in cron again and … yeah, I think I’m basically back to where I was before it went south.

All in all: saved by the backup. Not many tears. Phew this time.

Open Source, Technology

Hacking embedded day 2014

Once again our gracious sponsor Enea hosted an embedded hacking day arranged through foss-sthlm – the third time in three years at the same place with the same host. Fifty something happy hackers brought their boards, devices, screens, laptops and way too many cables to the place on a Saturday to spend it in the name of embedded systems. With no admission fee at all. Just bring your stuff, your skills and enjoy the day.

This happened on May 24th and on the outside of the windows we could identify one of the warmest and nicest spring/summer days so far this year in Stockholm. But hey, if you want to get some fun hacks done we mustn’t let those real-world things hamper us!

the room

All attendees were given atshirt tshirt and then they found themselves a spot somewhere in the crowd and the socializing and hacking could start. I got the pleasure of loudly interrupting everyone once in a while to say welcome or point out that a talk was about to begin…

We also collected random fun hardware pieces donated to us by various people for a hardware raffle. More about that further down.

Talk

To spice up the day of hacking, we offered some talks. First out was…

Bluetooth and Low Power radio by  Mats Karlsson and during this session we got to learn a bunch about hacking extremely low power devices and doing radio for them with Arduinos and more.

Mats talks bluetooth

We hadn’t much more than started but the clock showed lunch time and we were served lunch!

Contest

Readers of my blog and previous attendees of any of the embedded hacking days I’ve been organizing should be familiar with the embedded Linux contests I’ve made.

Lately I’ve added a new twist to my setup and I tested it previously when I visited foss-gbg and ran a contest there.

Basically it is a complicated maze/track that you walk through by answering questions, and when you reach the goal you have collected a set of words along the way. Those words should then be rearranged to form a question and that final question should be answered as fast as possible.

Daniel explains

Since I already blogged and publicized my previous “Parallell Spaghetti Decode” contest I of course had a new map this time and I altered the set questions a bit as well, even if participants in the latter can find similarities in the previous one. This kind of contest is a bit complicated so for this I hand out the play field and the questions on two pieces of paper to each participant.

After only a little over seven minutes we had a winner, Yann Vernier, who could walk home with a brand new Nexus 7 32GB. The prize was, as so much else this day, donated by Enea.

Hardware Raffle

I donated my Arduino Nano (never even unpacked) and a Raspberry Pi with SD-card that I never use. Enea pooled in with a Parallella board and we got an RFduino and a Texas Instrument Stellaris ARM-based little round robot. The Parallella board was the by far most popular device (as expected really) with the Stellaris board as second. Only 12 people signed up for the Rpi…

Parallella board

Everyone who was interested in one of the 5 devices signed up on a list, marking each thing of interest.

.Stellaris

We then put little pieces of paper with numbers on them in a big bowl and I got to draw 5 numbers (representing different individuals) who then won the devices. It of course turned out we did it in a complicated way that I had did some minor mistakes in to add to the fun. In the end I believe it was at least a fair process that didn’t give any favors or weight in any particular way. I believe we got 5 happy winners.

Workshop

“How to select hardware” was the name of the workshop I lead. Basically it was a one hour group discussion around how to buy, find, order, deal with, not do, avoid when looking for hardware for your (hobby) project. Discussions around brands, companies, sites, buying from China or Ebay, reading reviews, writing reviews, how people do when they buy things when building stuff of their own.

Workshop attendees

I think we had some good talks and lots of people shared their experiences, stories and some horror stories. Hopefully we all brought a little something with us back from that…

muffins

After that we refilled our coffee mugs and indulged in the huge and tasty muffins that magically had appeared.

Something we had learned from previous events was to not “pack” too many talks and other things during the day but to also allow everyone to really spend time on getting things done and to just stroll around and talk with others.

Instead of a third slot for a talk or another workshop we had a little wishlist in our wiki for the day, and as a result I managed to bully Björn Stenberg to the room where he then described his automated system for his warming cupboard (värmeskÃ¥p) which basically is a place to dry clothes. Björn has perfected his cupboard’s ability to dry clothes and also shut off/tell him when they are dry and not waste energy by keep on warming using damp sensors, Arduinos and more.

Bjorn's controller box

With that we were in the final sprint for the day. The last commits were made. The final bragging comments described blinking leds. Cables were detached. Bags were filled will electronics. People started to drop off.

Only a few brave souls stayed to the very end. And they celebrated in style.

Jämtlands IPA

I had a great day, and I received several positive comments and feedback from participants. I hope we’ll run a similar event again soon, it’d be great to keep this an annual tradition.

The pictures in this blog post are taken by: me, Jon Aldama, Annica Spangholt, Magnus Sandberg and Jämtlands bryggerier. Thanks! More pictures can also be found in Enea’s blog posting and in the Google+ event.

Thanks also to Jon, Annica and Sofie for the hard hosting work during the event. It made everything run smooth and without any bumps!

cURL and libcurl, libssh2, Network, Open Source

Why SFTP is still slow in curl

Okay, there’s no point in denying this fact: SFTP transfers in curl and libcurl are much slower than if you just do them with your ordinary OpenSSH sftp command line tool or similar. The difference in performance can even be quite drastic.

Why is this so and what can we do about it? And by “we” I fully get that you dear reader think that I or someone else already deeply involved in the curl project should do it.

Background

I once blogged a lengthy post on how I modified libssh2 to do SFTP transfers much faster. curl itself uses libssh2 to do SFTP so there’s at least a good start. The problem is only that the speedup we did in libssh2 was because of SFTP’s funny protocol design so we had to:

  1. send off requests for a (large) set of data blocks at once, each block being N kilobytes big
  2. using a several hundred kilobytes big buffer (when downloading the received data would be stored in the big buffer)
  3. then return as soon as there’s one block (or more) that has returned from the server with data
  4. over time and in a loop, there are then blocks constantly in transit and a number of blocks always returning. By sending enough outgoing requests in the “outgoing pipe”, the “incoming pipe” and CPU can be kept fairly busy.
  5. never wait until the entire receive buffer is complete before we go on, but instead use a sliding buffer so that we avoid “halting points” in the transfer

This is more or less what the sftp tool does. We’ve also done experiments with using libssh2 directly and then we can reach quite decent transfer speeds.

libcurl

The libcurl transfer core is basically the same no matter which protocol that is being transferred. For a normal download this is what it does:

  1. waits for data to become available
  2. read as much data as possible into a 16KB buffer
  3. send the data to the application
  4. goto 1

So, there are two problems with this approach when it comes to the SFTP problems as described above.

The first one is that a 16KB buffer is very small in SFTP terms and immediately becomes a bottle neck in itself. In several of my experiments I could see how a buffer of 128, 256 or even 512 kilobytes would be needed to get high bandwidth high latency transfers to really fly.

The second being that with a fixed buffer it will come to a point every 16KB byte where it needs to wait for that specific response to come back before it can continue and ask for the next 16KB of data. That “sync point” is really not helping performance either – especially not when it happens so often as every 16KB.

A solution?

For someone who just wants a quick-fix and who builds their own libcurl, rebuild with CURL_MAX_WRITE_SIZE set to 256000 or something like that and you’ll get a notable boost. But that’s neither a nice nor clean fix.

A proper fix should first of all only be applied for SFTP transfers, thus deciding at run-time if it is necessary or not. Then it should dynamically provide a larger buffer and thirdly, for upload it should probably make the buffer “sliding” as in the libssh2 example code sftp_write_sliding.c.

This is also already mentioned in the TODO document as “Modified buffer size approach“.

There’s clearly room for someone to step forward and help us improve in this area. Welcome!

curl dot-to-dot

Network, Security, Web

Less plain-text is better. Right?

8 Comments

Every connection and every user on the Internet is being monitored and snooped at to at least some extent every now and then. Everything from the casual firesheep user in your coffee shop, an admin in your ISP, your parents/kids on your wifi network, your employer on the company network, your country’s intelligence service in a national network hub or just a random rogue person somewhere in the middle of all this.

My involvement in HTTP make me mostly view and participate in this discussion with this protocol primarily in mind, but the discussion goes well beyond HTTP and the concepts can (and will?) be applied to most Internet protocols in the future. You can follow some of these discussions in the httpbis group, the UTA group, the tcpcrypt list on twitter and elsewhere.

IETF just published RFC 7258 which states:

Pervasive Monitoring Is a Widespread Attack on Privacy

Passive monitoring

Most networking surveillance can be done entirely passively by just running the correct software and listening in on the correct cable. Because most internet traffic is still plain-text and readable by anyone who wants to read it when the bytes come flying by. Like your postman can read your postcards.

Opportunistic?

Recently there’s been a fierce discussion going on both inside and outside of IETF and other protocol and standards groups about doing “opportunistic encryption” (OE) and its merits and drawbacks. The term, which in itself is being debated and often is said to be better called “opportunistic keying” (OK) instead, is about having protocols transparently (invisible to the user) upgrade plain-text versions to TLS unauthenticated encrypted versions of the protocols. I’m emphasizing the unauthenticated word there because that’s a key to the debate. Recently I’ve been told that the term “opportunistic security” is the term to use instead…

In the way of real security?

Basically the argument against opportunistic approaches tends to be like this: by opportunistically upgrading plain-text to unauthenticated encrypted communication, sysadmins and users in the world will consider that good enough and they will then not switch to using proper, strong and secure authentication encryption technologies. The less good alternative will hamper the adoption of the secure alternative. Server admins should just as well buy a cert for 10 USD and use proper HTTPS. Also, listeners can still listen in on or man-in-the-middle unauthenticated connections if they capture everything from the start of the connection, including the initial key exchange. Or the passive listener will just change to become an active party and this unauthenticated way doesn’t detect that. OE doesn’t prevent snooping.

Isn’t it better than plain text?

The argument for opportunism here is that there will be nothing to the user that shows that it is “upgrading” to something less bad than plain text. Browsers will not show the padlock, clients will not treat the connection as “secure”. It will just silently and transparently make passive monitoring of networks much harder and it will force actors who truly want to snoop on specific traffic to up their game and probably switch to active monitoring for more cases. Something that’s much more expensive for the listener. It isn’t about the cost of a cert. It is about setting up and keeping the cert up-to-date, about SNI not being widely enough adopted and that we can see only 30% of all sites on the Internet today use HTTPS – for these reasons and others.

HTTP:// over TLS

In the httpbis work group in IETF the outcome of this debate is that there is a way being defined on how to do HTTP as specified with a HTTP:// URL – that we’ve learned is plain-text – over TLS, as part of the http2 work. Alt-Svc is the way. (The header can also be used to just load balance HTTP etc but I’ll ignore that for now)

Mozilla and Firefox is basically the only team that initially stands behind the idea of implementing this in a browser. HTTP:// done over TLS will not be seen nor considered any more secure than ordinary HTTP is and users will not be aware if that happens or not. Only true HTTPS connections will get the padlock, secure cookies and the other goodies true HTTPS sites are known and expected to get and show.

HTTP:// over TLS will just silently send everything through TLS (assuming that it can actually negotiate such a connection), thus making passive monitoring of the network less easy.

Ideally, future http2 capable servers will only require a config entry to be set TRUE to make it possible for clients to do OE on them.

HTTPS is the secure protocol

HTTP:// over TLS is not secure. If you want security and privacy, you should use HTTPS. This said, MITMing HTTPS transfers is still a widespread practice in certain network setups…

TCPcrypt

I find this initiative rather interesting. If implemented, it removes the need for all these application level protocols to do anything about opportunistic approaches and it could instead be handled transparently on TCP level! It still has a long way to go though before we will see anything like this fly in real life.

The future will tell

Is this just a fad that will get no adoption and go away or is it the beginning of something that will change how we do protocols in the future? Time will tell. Many harsh words are being exchanged over this topic in many a debate right now…

(I’m trying to stick to “HTTP:// over TLS” here when referring to doing HTTP OE/OK over TLS. This is partly because RFC2818 that describes how to do HTTPS uses the phrase “HTTP over TLS”…)

Mozilla, Network, Open Source, Web

licensed to get shared

As my http2 presentation is about to get its 16,000th viewer over at Slideshare I just have to take a moment and reflect over that fact.

Sixteen thousand viewers. I’ve uploaded slides there before over the years but no other presentation has gotten even close to this amount of attention even though some of them have been collecting views for years by now.

http2 presentation screenshot

I wrote my http2 explained document largely due to the popularity of my presentation and the stream of questions and curiosity that brought to life. Within just a couple of days, that 27 page document had been downloaded more than 2,000 times and by now over 5000 times. This is almost 7MB of PDF which I believe raises the bar for the ordinary casual browser to not download it without having an interest and intention to at least glance through it. Of course I realize a large portion of said downloads are never really read.

Someone suggested to me (possibly in jest) that I should convert these into ebooks and “charge 1 USD a piece to get some profit out of them”. I really won’t and I would have a struggle to do that. It has been said before but in my case it is indeed true: I stand on the shoulders of giants. I’ve just collected information and written down texts that mostly are ideas, suggestions and conclusions others have already made in various other forums, lists or documents. I wouldn’t feel right charging for that nor depriving anyone the rights and freedoms to create derivatives and continue building on what I’ve done. I’m just the curator and janitor here. Besides, I already have an awesome job at an awesome company that allows me to work full time on open source – every day.

The next phase started thanks to the open license. A friendly volunteer named Vladimir Lettiev showed up and translated the entire document into Russian and now suddenly the reach of the text is vastly expanded into a territory where it previously just couldn’t penetrate. With using people’s native languages, information can really trickle down to a much larger audience. Especially in regions that aren’t very Englishified.