Every web developer should know about the Secure Sockets Layer and it’s successor, the Transport Layer Security. (SSL and TLS.) These techniques are nowadays a requirement to keep the Internet secure and to keep private matters private. But while this technique is great, the implementation of it has some flaws.
Flaws that aren’t easy to resolve, though. But to understand, you will need to understand how this technique works when you use it to protect the communication between a visitor and a website.
This is a very long post as it is a complex topic and I just don’t want to split it in multiple posts. So I add several headers to separate parts…
What is SSL?
When you communicate with a website, you’re basically have a line with two endpoints. You on one side and the web server on the other side. But this isn’t a direct line but goes from your computer to your router/modem, to your provider, over some other nodes on the Internet, to the provider of the host, the router of the host to the computer where the host is running the website on. And this is actually a very simplified explanation!
But it shows a problem. The communication between the two endpoints goes over various node and at every node, someone might be monitoring the communication, listening for sensitive information like usernames, passwords, social security numbers, credit card numbers and whole lot more. And to make it even more harder, you don’t know if your information will travel over nodes that you can trust! So, you need to make sure that the information you send over between both endpoints is secure. And that’s where SSL is used.
SSL is an encryption technique with asynchronous keys. That means that the host has a private key and a public key. It keeps the private key hidden while giving everyone the public key. You can generally use one key to encrypt a message but you would need the other key to decrypt it again. And that’s basically how security works! You have the public key and you encrypt your data with it before sending it to me. No one on those nodes have the private key, except me, so I’m the only one who can decrypt it. I can then encrypt a response with the private key and send that back to you, as you can decrypt it again with the public key.
Unfortunately, everyone on those nodes can too, as they would all know this public key as I had just sent it to you. So things need to be a little more secure here. Which fortunately is the case. But in general, you should never encrypt sensitive data with a private key as anyone with the public key would be able to read it!
But the Internet uses a better trick. Once you receive the public key from the web server, your browser will generate a session key, which is a synchronous encryption key. This session key can be used by anyone who knows it and right now, you would be the only one. But as you have my public key, you would use my public key to encrypt the session key and send it to me. Now I know it too and we can have a communication session using this session key for security. And once the session is done, the session key can be discarded as you would make a new one for every session.
Most people think the encryption is done using the SSL certificates but that’s not the case! SSL is only used to send a session key to the server so both can communicate safely. That is, as long as no one else knows that session key. Fortunately, session keys are short-lived so there isn’t much time for them to fall in the wrong hands…
The main weakness…
So, this seems pretty secure, right? My site sends you a public key, you create a session key and then we communicate using this session key and no one who is listening in on us can know what we are talking about! And for me it would be real easy to make the SSL certificate that would be used as most web servers can do this without any costs, and generally within just a few minutes. So, what can go wrong?
Well, the problem is called the “Man in the Middle” attack and this means that one of the nodes on the line will listen in on the communication and will intercept the request for secure communications! It will notice that you ask for a public key so it will give its own public key to you instead that of the host. It also asks for the public key of the host so it can relay all communications. You would then basically set up a secure line with the node and the node does the same with the host and will be able to listen in to anything that moves between you, as it has to decrypt and then encrypt each and every message. So, it can listen to sensitive data without you realizing that this is happening!
So the problem is that you need to know that the public key I gave you is my public key, and not the key of this node. How do you know for sure that this is my key? Well, this is where the Certificate Authorities (CA) have a role.
The CA has a simple role of validating the certificates that I use for my website. I want to secure my host so I make a certificate. I then ask the CA to sign this certificate for me. The CA then checks if I really am the owner of the domain at that specific moment or have at least some control over the domain. And when they believe that I’m the owner, they will sign my certificate.
Then, when you receive my public key then you can check the credentials of this certificate. It should tell you if it is for the specific domain that you’re visiting and it should be signed by the CA who issued the certificate. If it is signed correctly then the CA will have confirmed that this certificate is linked to my host and not that of some node between you and me.
But the problem is that when your connection isn’t secure because some node is trying to listen than checking if my certificate is properly signed by the CA won’t work, as you would be requesting the CA to validate it over the same unsafe connection. The node will just claim it is so that option won’t work. No, you already need to know the public key of the CA on your system so you can decrypt my signature. And you need to have received the Ca’s certificate from some secure location. Otherwise, you can’t trust if my public key is the real thing.
So most web browsers have a list of public keys as part of their setup. When they install themselves, they will also include several trustworthy public keys from the more popular CA’s. Basically, the CA’s they deem reliable. So your browser will validate any public key from my site with the public keys it knows and trusts and if everything is okay, you will be notified that the connection is secure and the session key can be generated for further secure communications.
Otherwise, your browser will give you a warning telling you what’s wrong with the certificate. For example, it might be outdated or not meant for the specific domain. In general, you should not continue as the connection with the host has security problems!
But here’s the thing… The list of trusted CA’s in your browser can be modified and to be honest, it sometimes gets modified for various reasons. Some are legitimate, others are not.
For example, this list is modified when a specific CA is deemed unreliable. This happens regularly with smaller CA’s but once in a while, some major scandal happens. For example, in 2011 it was discovered that the company DigiNotar had a security breach which had resulted in several certificates being falsified. Most likely, the Iranian Government was behind this in an attempt to check all emails that their citizens were sending through GMail. The fake certificates allowed them to listen in on all emails using the man in the middle technique. DigiNotar went bankrupt shortly afterwards, as all the certificates they had issued had become worthless.
Similar problems occurred at StartCom, a CA that actually gave away free certificates. The Israeli company was purchased by a Chinese company and some suspicious behavior happened soon afterwards. The fear was that this Chinese company (and perhaps even the Chinese government) would use this trust that StartCom had to make fake certificates to listen in on all communications in China. Both Mozilla and Google started to raise questions about this and didn’t get satisfying answers so they decided to drop the StartCom certificates. This CA had become controversial.
And then there’s Symantec. Symantec is a company that has been making software for decades that all relate to security. It is an American company and has been trustworthy for a long time. And in 2010 Symantec acquired Verisign’s authentication business unit which includes releasing SSL certificates for websites. But in 2015 it was discovered by Google that Symantec had issued several test certificates for impersonating Google and Opera. Further research has led Google to believe that Symantec has been publishing questionable certificates for over 7 years now and thus they announced that they will distrust Symantec SSL certificates in the near future. In April 2018, all Symantec certificates will be useless in Google Chrome and other browsers might follow soon.
Also interesting is that Symantec is selling their SSL business to DigiCert. This could solve the problem as DigiCert is still trusted. Or it makes things worse when browser manufacturers decide to distrust DigiCert from now on also.
But also: Telecom!
But there are more risks! Many people nowadays have mobile devices like tablets and phones. These devices are often included with a subscription to services of some mobile phone company. (T-Mobile and Vodafone, for example.) These companies also sell mobile devices to their customers and have even provided “free phones” to new subscriptions.
However, these companies will either provide you with a phone that has some of their software pre-installed on your new device or will encourage you to install their software to make better use of their services. The manufacturers of these mobile devices will generally do similar things if given a chance. And part of these additions they make to your Android or IOS device is to include their own root certificates with the others. This means that they are considered trustworthy by the browser on your device.
Is that bad? Actually, it is as it allows these companies to also do a man in the Middle attack on you. Your telecom provider and the manufacturer of your phone would be able to listen to all your data that you’re sending and receiving! This is worse, as local government might require these companies to listen in on your connection. It is basically a backdoor to your device and you should wonder why you would need to trust your provider directly. After all, your provider is just another node in your connection to the host.
Did you check the certificate?
So the problem with SSL is that it’s as reliable as the Certificate Authorities who made those certificates. It’s even worse if your device has been in the hands of someone who wants to listen in on your secure connections as they could install a custom trusted certificate. Then again, even some malware could install extra public keys in your trusted certificates list without you noticing. So while it is difficult to listen to your secure conversations, it is not impossible.
You should make a habit of checking any new SSL certificate that you see pop up in your browser and it would be a good idea if browsers would first ask you to check a certificate whenever they detect that a site has a new one. It would then be up to the user to decide to trust the certificate or not. And those certificates would then be stored so the browser doesn’t need to ask again.
Unfortunately, that would mean that you get this question to trust a certificate very often when you’re browsing various different sites and users will tend to just click ‘Ok’ to get rid of the question. So, that’s not a very good idea. Most users aren’t even able to know if a certificate is trustworthy or not!
For example, while you’re reading this blog entry, you might not have noticed that this page is also a secured page! But did you check the certificate? Did you notice that it is signed by Automattic and not by me? That it’s a certificate issued by “Let’s Encrypt“? Well, if the certificate is showing this then it should be the right one. (But when my host Automattic changes to another CA, this statement becomes invalid.)
And here things become interesting again. “Let’s Encrypt” gives away free certificates but they are only valid for a short time. This makes sense as domains can be transferred to other owners and you want to invalidate the old owner’s certificates as soon as possible. It uses a protocol called ACME which stands for “Automatic Certificate Management Environment. It’s basically a toolkit that will automate the generation of certificates for domains so even though the certificates are only valid for a short moment, they will be replaced regularly. This is a pretty secure setup, although you’d still have to trust this CA.
Problem is that “Let’s Encrypt” seems to prefer Linux over Windows as there is almost no good information available on how to use ACME on Windows in IIS. But another problem is that this protocol is still under development and thus still has some possible vulnerabilities. Besides, it is very complex, making it useless for less technical developers. The whole usage of certificates is already complex and ACME doesn’t make things easier to understand.
Also troublesome is that I tried to download the ACME client “Certify the Web” for Windows but my virus scanner blocked the download. So, now I have to ask myself if I still trust this download. I decided that it was better not to trust them, especially as I am trying to be secure. Too bad as it seemed to have a complete GUI which would have made things quite easy.
Don’t ignore security warnings! Not even when a site tells you to ignore them…
Another problem with SSL is that it is an expensive solution so it is disliked by many companies who are hosting websites. It’s not the cost for the certificates, though. It’s the costs for hiring an expert on this matter and making sure they stay with the company! A minor issue is that these security specialists do have access to very sensitive material for companies so you need to be sure you can trust the employee.
Of course, for very small companies and developers who also host websites as a hobby, using SSL makes things a bit more expensive as the costs are generally per domain or sub domain. So if you have three domains and 5 subdomains then you need to purchase 8 certificates! That’s going to easily cost hundreds of euros per year. (You could use a Multi-Domain (SAN) Certificate but that will cost about €200 or more per year.)
Plus, there’s the risk that your CA does something stupid and becomes distrusted. That generally means they will have to leave the business and that the certificates you own are now worthless. Good luck trying to get a refund…
But another problem is that the whole Internet is slowly moving away from insecure connections (HTTP) to secure (HTTPS) connections, forcing everyone to start using SSL. Which is a problem as it starts to become a very profitable business and more and more malicious people are trying to fool people into buying fake or useless certificates or keep copies of the private key so they can keep listening to any communications done with their keys. This security business has become highly profitable!
I don’t know if there are better solutions. The problem is very simple: Man in the Middle. And the biggest problem with MITM is that he can intercept all communications so you need something on your local system that you already can trust. Several CA’s have already been proven untrustworthy so who do you trust? How do you make sure that you can communicate with my server without any problems?
There is the Domain Name Service but again, as the MITM is intercepting all your transactions, they can also listen in on DNS requests and provide false information. So if a public key would be stored within the DNS system, a node can just fake this when you request for it. The MITM would again succeed as you would not be able to detect the difference.
So maybe some kind of blockchain technology? Blockchains have proven reliable with the Bitcoin technology as the only reason why people have lost bitcoins is because they were careless with the storage of their coins. Not because the technique itself was hacked. And as a peer-to-peer system you would not need a central authority. You just need to keep the blocks on your system updated at all times.
As we want the Internet to be decentralized, this technology would be the best option to do so. But if we want to move security into blockchains then we might have to move the whole DNS system into a blockchain. This would be interesting as all transactions in blockchains are basically permanent so you don’t have to pay a yearly fee to keep your domain registered.
But this is likely to fail as Bitcoin has also shown. Some people have lost their bitcoins because their disks crashed and they forgot to make a copy of their coins. Also, the file size of the Bitcoin blockchain has grown to 100 GB of data in 2017 which is quite huge. The whole DNS system is much bigger than Bitcoin is so it would quickly have various problems. Your browser would need to synchronize their data with the network which would take longer and longer as the amount of data grows every day.
So, no. That’s not really a good option. Even though a decentralized system sounds good.
So, SSL has flaws. Then again, every security system will have flaws. The main flaw in SSL is that you need to trust others. And that has already proven to be a problem. You have to be ultra-paranoid to want to avoid all risks and a few people are this paranoid.
Richard Stallman, for example, is a great expert on software yet he doesn’t use a mobile phone and avoids using the Internet directly. Mobile phones are “portable surveillance and tracking devices” so he won’t use them. He also avoids key cards and other items that allow people to track wherever he goes. And he generally doesn’t access the Web directly, as this too would allow people to track what he’s doing. (He does use Tor, though.) And maybe he’s on to something. Maybe we are putting ourselves in danger with all this online stuff and various devices that we have on our wrists, in our pockets and at our homes.
Thing is that there is no alternative for SSL at this moment so being paranoid is useful to protect yourself. Everyone should be aware of the risks they take when they visit the Internet. This also depends on how important or wealthy you are, as poor, boring people are generally not interesting for malicious people. There isn’t much to gain from people with no money.
Still, people are still too careless when they’re online. And SSL isn’t as secure as most people think, as events from the past have already proven…