Self-signed certificates and Firefox 3 - a possible solution

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Some websites need to handle data securely and assure the end-user they are a) secure and b) who they say they are. The traditional way to achieve these is via Secure Socket Layer. Firefox 3 changed what happens when a self-signed SSL certificate is encountered. It's a change which has caused some concern and much discussion.

Should we only trust certificates signed by third parties? Are there cases where using a self-signed certificate is valid? Should users be informed or warned and how strong should the language of that notification be? Is it possible a simple solution is already available but has been overlooked in all the flan-flinging? I think so.

What's the fuss about?

SSL is essentially an encryption methodology used to create a tunnel between the browser session and the server. Anybody listening can hear but not decrypt the traffic because they don't possess either of the relevant keys. The problem is when a user goes to a site -- set up by an unsavoury third party -- which pretends to be the secure site. The site and domain closely resemble the real one and the traffic is all being encrypted but it is all going to wrong place. At this point certification enters the fray. The theory is that on entering the site, the browser is presented with an SSL certificate. If that certificate has been signed and approved by an independent certification authority (CA) then the browser assumes all is well and proceeds. If it doesn't then the browser lets the user know.

Mozilla's change of policy revolves around this notification. Whereas it used to say "we're not sure about this but you can accept if you want" -- and most users blindly accepted it anyway, it now says "We can't guarantee this and that might be because the server is doing something nasty, please jump through this hoop to proceed anyway" at which most users will be justifiably concerned and not proceed. I've paraphrased there but the essence is correct.

Where does self-signing come into it?

Self signed certificates are ones that are signed by the same server that hosts the site -- that is the people providing the certificate are also and at the same time saying "don't worry you can trust me". You can see why there is concern over not warning users about these kinds of certificates, but certificates signed by a CA cost quite a bit and to have one for a internal server which nevertheless needs to be secure could be seen as an expense most organisation do not want to go with. An example of this might be a webmail server which presents mail to disparate users over the internet but does not want the traffic to be in the public domain. A self-signed certificate is the most cost-effective option here, but making every new user perform a number of tasks just to accept the certificate is not something many IT managers would relish. I should note that CAs with zero or minimal cost certificates do exist but the browsers don't always know about them or contain their details; so, certificates signed by them are treated like self-signed certificates.

Aside from some valid reasons for using self-signed certificates, there are also those who just plain do not like the idea of passing trust through a third party, particularly one who is in the business of making money. I've seen genuine concerns over allowing one business (as opposed to an independent NGO for example) to effectively control whether customers of another business are told it is safe to use.

The two sides

So one side of this discussion says that Mozilla should use all it's persuasion to warn users of the dangers of self-signed certificates and that without CAs there is no way to determine the authenticity of the certificate being provided by a website. The other side says Mozilla should not use such "scaremongering" language that through Mozilla adopting this policy "some sites are forced to pay for certificates that they otherwise wouldn’t have bought [and others] are forced to go without encryption that they otherwise would have had" (see the blog I linked to earlier). You'll note that both sides focus on the fact that third parties are needed to sign the certificate. Perhaps we're looking at this the wrong way.

Another way

Certificates do not need to authenticated against a third party as much as an independent source. This needs to be a source which cannot be changed quickly and the data upon which is held on and supplied by somebody other than the webserver and it's owners.

Within the DNS records for any domain there are a number of things listed. For example the MX record will tell you what servers are preferred for inbound mail for that domain. There is a record which to me seems designed for our purposes here, the SSHFP record. This is designed to contain SSH key fingerprints. This is a quote from RFC4255 which defines this record type:

Upon connection to an SSH server, the SSH client MAY look up the SSHFP resource record(s) for the host it is connecting to. If the algorithm and fingerprint of the key received from the SSH server match the algorithm and fingerprint of one of the SSHFP resource record(s) returned from DNS, the client MAY accept the identity of the server.

What's more public DNS data is stored on central servers and not provided by the webserver, indeed if the DNS data is faked then the user is not going to the correct server for that domain and perhaps has some bigger issues to worry about.

A browser that is presented with a certificate for a site could check whether the certificate is signed by a CA and/or whether the certificate fingerprint matches that in the SSHFP record for the same domain. In this way a self-signed certificate can have its key fingerprint stored in the domain DNS records without having to pay anybody and for those who want the extra reassurance for their customers they can pay for their certificate to be signed as now.

The browser doesn't have to do the DNS request: it simply asks the DNS server for the contents of the SSHFP record for that domain if required. There will be a slight delay while it does this, but if you want your users to avoid this you can pay for a CA to sign your certificate. If a certificate is signed but cannot be authenticated by a CA or the DNS record, then the browser is at liberty to present a warning to the user. At present I imagine many domains do not have anything in their SSHFP record, but if they want to use self-signed certificates they will certainly do so if the browser adopted this policy.

Puts on flame-proof suit

I imagine (but hope not) by this point a number of DNS and SSL/SSH experts will be reaching for their keyboard to shoot me down. If that's the case please do so. I am an expert in neither but I do use them so this is my suggestion for a cost-effective resolution as I see it. If I am wrong tell me why, please, but if I am not or if my idea has merit, where do we go from here?



Terry Hancock's picture

Interesting subject...

So, you're saying that the reason why 3rd party certificates are important is to verify the identity of the server? (I.e. to avoid a man-in-the-middle attack of some kind?)

To be honest, I had thought the point was to register approval of the (real) site with a 3rd party trust network (which always sounded like a racket to me, to be honest).

Under that assumption, I've generally taken the attitude that, if I trust the site (or site owner) that I can trust the SSH without a certificate authority. This is something I usually encounter with account-membership sites, where there isn't anything really serious at risk, so I haven't felt the need to study it too hard.

Ryan Cartwright's picture

So, you're saying that the reason why 3rd party certificates are important is to verify the identity of the server? (I.e. to avoid a man-in-the-middle attack of some kind?)

Well no, that's the main reason the third parties and the supporters of CAs give. Personally I don't buy that as a valid reason. I can see the assurance that CAs could give to end-users but that's only because the users are told the CAs are trustworthy (coincidentally by the CA themselves :o) ).

To be honest, I had thought the point was to register approval of the (real) site with a 3rd party trust network (which always sounded like a racket to me, to be honest).

Me too. The whole system ask you to move your trust from the site owner to a third party neither of whom you may know or otherwise trust. Yet if a browser is to tell you a site is encrypted (with a padlock icon) then surely it should tell you if it cannot verify that the site is who they claim to be. My suggestion above gives a practical way to check this without requiring every sub-domain to pay the "racketeers".


gkanai's picture
Submitted by gkanai on

Ryan, your proposal is interesting but as it is not something that is implementable today, it's something of a moot point with reference to software that Mozilla has to ship today.

Johnathan Nightingale, who works at Mozilla on security and user interfaces for security, has a detailed post up recently on this particular issue that I think would be worth your while to peruse.

Note that "Several CAs accepted by all major browsers sell certificates for less than $20/yr, and StartSSL, in the Firefox 3 root store, offers them for free." So the financial complaint should be disregarded.

Also, Johnathan is calling for additional help:

"I don’t think the approach in Firefox 3 is perfect, I’m not sure any of us do. I have filed bugs, and talked about things I think we could do to continue to enhance our users’ security while at the same time reducing unnecessary annoyances. "

Full disclosure: I work at Mozilla but not in the area in question.

Ryan Cartwright's picture

Ryan, your proposal is interesting but as it is not something that is implementable today, it's something of a moot point with reference to software that Mozilla has to ship today.

Care to explain why? Really, I would like to know. I haven't had a chance to read Johnathan's post but I will - thanks for the link.

The cost may be nullified by things like StartSSL (and I didn't know the root was in Firefox 3 - thanks) but there are still some who question whether using a third party in the first place is the right way to go (I'm not necessarily one of them).


Epicanis's picture
Submitted by Epicanis on

It's not clear how many DNS projects support this field yet - if it's not widely supported by implemented DNS systems it won't do much good.

It also wouldn't necessarily solve what *I* see as the problem with Firefox's crusade against self-signed certificates. Unless one is also hosting one's own DNS, you would then still effectively need to beg a third party (your DNS host) to permit you to encrypt your server's traffic.

I mentioned this in my post over at the discussion on, but what's so horribly jarring about this is having "free and open" Mozilla Firefox now insisting that you cannot possibly encrypt your traffic without help and permission from a "professional" third party. I realize that's not what the new UI is supposed to do, but it is, and it runs directly against what I always thought truly "free" software was supposed to be about.

All that said, I still actually like the idea of using SSHFP records, I'm just not sure if it would be enough to solve the problem.

Ryan Cartwright's picture

It also wouldn't necessarily solve what I see as the problem with Firefox's crusade against self-signed certificates. Unless one is also hosting one's own DNS, you would then still effectively need to beg a third party (your DNS host) to permit you to encrypt your server's traffic.

Why? The certificate signature is stored in the SSHFP record and can be done so in plain text as only the real certificate can generate a matching signature -- can't it?


Epicanis's picture
Submitted by Epicanis on

That's correct but that's not what I mean.

What I mean is, unless I am running my OWN DNS (and have direct access to the DNS configuration) I still have to go beg my DNS host to add an SSHFP record for me (assuming the hosts's DNS supports that field).

It's not that this is necessarily an onerous request, really, just that it means if you're not running your own Domain Name Servers, all you've accomplished is to change which "third party" gets to decide whether or not you're allowed to encrypt your traffic (from a "Certificate Authority" to a "DNS hoster").

It's the fact that Mozilla is effectively (though I assume unintentionally) *requiring* people to go get approval from some third party to provide encryption that's really bugging me here.

Also, how long before et al decide to charge an extra $5/month for this "service"?

mossholderm's picture

The issue with using something like SSHFP is that many attacks against web sites are DNS based.

It could be via domain typos (e.g. vs. or via DNS poisoning (where the attacker makes the client think the DNS records for the site says X.X.X.X instead of Y.Y.Y.Y). In either case, the client would be presented with a falsified SSHFP record, and happily continue on.

The only way something like this would work would be in combination with DNSSEC, which permits signed DNS responses, so you know they are coming from the real DNS server. But that isn't likely to happen on the general internet for a long, long time.

My suggestion to sites that want to use self signed certs is to have them create a CA and hand out the CA certificate for people to install. Once it is installed, you'll KNOW you are talking to the correct server.

Ryan Cartwright's picture

As I said in the article if the user s a victim of "DNS poisoning" then they have bigger issues. Let's not forget there is a side issue of user education here. It could be said that prompts like the Mozilla one do more to scare than educate users.

You're right in that users who were not paying attention could be caught by phishing sites that used SSHFP but it's entirely plausible that those same users may not notice that a fake site is not encrypted at all. In the end there is no substitute for user awareness.

Your solution is what should happen now but sometimes becoming your own CA and getting users to install it becomes such a pain that it's not worth the effort. I like your idea - I've used it myself but if it was really worth the effort it would be more in use now but it's not. It also doesn't resolve the issue that the same party is providing the certificate and the verification. You're asking a user to trust your site by using a root certificate stored on your site. DNSSEC is a good idea and although it and SSHFP are not so well used now, a key browser like Firefox providing support for such services will enhance their popularity.

thanks for the feedback though. As said you've raised some good points.

Terry Hancock's picture

You’re right in that users who were not paying attention could be caught by phishing sites that used SSHFP but it’s entirely plausible that those same users may not notice that a fake site is not encrypted at all. In the end there is no substitute for user awareness.

Hmm. Well, I would certainly know if a site wasn't using encryption at all.

How would I know if I were a victim of "DNS poisoning", though? My understanding of DNS/BIND is pretty foggy. I would guess that it would be the top level DNS server that I reference that would actually be the "victim" in this scenario, and that the "poisoning" would be somewhere in the tree of hand-offs that happens when a DNS look-up is done.

So how would I avoid the problem? My DNS is largely determined by my choice of ISP as far as I know.

Ryan Cartwright's picture

I was quite specific in using the term phishing but I guess I forgot the slight ambiguity of the term. I was referring to sites which misspell URIs ( as opposed to or those which use e-mail links so that the user will just click the link and not look at the actual URL. These sites could use SSHFP to provide a valid cerificate for the false domain and the user would be no wiser.

I very much doubt you would be caught out by URLs that were not what you wanted but there are a considerable amount of users who would be. At least I presume there must be by the fact that the technique is so widely used by those sending such e-mails.

If your ISPs DNS itself is compromised you probably have a legal case against your ISP. I'm not too familiar with all the facets of DNS poisoning myself but I assume it would involve hijacking a wireless connection with a MITM attack. Can an attacker alter the DNS routes of a wired connection?

As the GP suggested tying up SSHFP with DNSSEC would be a good start as the DNS record itself could be signed but that just brings us full circle to who signs the DNS record?

Don't forget that I'm talking about this as an alternative to self-signed certificates not a replacement for CA signing. If the site in question is public facing and requires some user reassurance then a CA is ideal. Having said that some fairly major sites use self-signed certs and provide them on their website, as I found out today this includes web access to an account.

Terry Hancock's picture

I'm still foggy on how DNS works, but it has been my understanding that it is a distributed database. So, my ISP's DNS asks up the hierarchy until it reaches some sort of master DNS server, which then searches down-tree through a hierarchy of DNS information providers, closer and closer to the target site's DNS server. Somewhere along the way, a server that knows what the URL maps to will respond, and that's the response I get back.

If that's true, then all that has to happen to inject a false DNS message that will get back to my system, is that one of the computers in that chain has to be compromised.

I thought I remembered reading about attacks of this nature actually being done in the past: a person types in the (exact) URL of (say), but they get a false IP in response to their DNS query, which then takes them to a phish site -- due to a problem in the way the DNS look-up itself is performed.

But I don't really see how you can protect yourself from this kind of attack -- it isn't really your system that's being attacked. Perhaps the only way would be to run a DNS caching system on your computer and generate warnings for suspicious IP changes. But I'm reasonably certain that I'm not running anything like that.

sitor's picture
Submitted by sitor on

Disclaimer 1: I have been working for a CA and support the need to certify identity information to build trust between different actors involved in remote transactions. The technology does not matter, but there needs to be a correct trust building through procedures that maximally rule out the possibility for identity theft (theft of server identity in this case). It is this kind of procedures that cost money, so even if you replace the PKI technology with other technology, if you want to have the same trust level, the cost will remain in the same order as for CA certificates.

Disclaimer 2: I don't know what DNSSEC is or does and whether or not it might solve any of the problems related to the issues I see with the ideas of the post above, but I suspect that at least the first one will remain (and that is the most severe one in my opinion).

In my opinion your reasoning is flawed for the following reason:
- DNS is supposed to give a link between the URL (destined to humans) and IP address (destined to machines). The information that is added to the DNS record is only informative, nothing more. This is a pure technical thing that is required to make the internet practically usable.
- PKI (CA's) are destined to bring trust between parties that do not see each other in real life (i.e. when it is easy for someone to present himself as someone he is not). The public key signed by a trusted CA helps to prevent such issues. This IS a pure security thing. And to make this work a CA (in any case a proper one) implements a lot of procedures and processes to ensure verifications are correctly carried out to check the identity of a holder of a key before certifying this information. Such strict procedures and processes are not present in a system such as DNS. And these will not be added lightly because these cost a lot of effort, thus time, thus money.

If you would use the DNS record information to go aside the PKI complexity (because complex it is indeed), you have to take into account the following two problems:

1. The information in the DNS record are not of the same level and can not at all be trusted in the same way as information certified by a CA. For the DNS of my own website they just put in what I told them to put in without any verification. There are even ISPs that offer you a control center to manage the DNS records yourself. This means that I could create a DNS record on the name of another company without anyone holding me back.

2. Even if the information in the DNS record would be trustworthy, then you loose the separation between the URL to IP linking and Site Identity guaranteeing. DNS is not a full proof protocol. There are ways to fraud with DNS (DNS spoofing). I don't know any details on how that works but the result is that if a user enters the correct URL, his PC will receive a wrong IP address and will be directed to the wrong server. If that site uses SSL with a proper certified public key (from a CA), the user will be notified by his browser that the certificate does not have the correct domain certified. If you work with the information from the DNS, and the browser accepts the information from the DNS records (which are spoofed), then there is no second verification mechanism and the user is not notified of a problem => hackers win!



Terry Hancock's picture

Trust is complicated... it's not a scalar.

Should I trust a CA to be as thorough as you say? (I notice you even threw in a few weasel words to avoid too strong of an endorsement). Should I trust them to care about sites like the one I'm running or the one I'm using? What about a DNS? Also, it has to be appreciated that different entities may be trusted, but only in certain domains. I may thoroughly trust the news accuracy of, say, the New York Times, but not trust them at all with my money. Likewise, I may very well trust my bank with my accounts, but not at all with honesty in reporting -- they are a biased source.

Furthermore, identity does not necessarily exclude anonymity. If the source you trust is someone on the internet who talks to you under the name "Seekret", then what you want to know about any given communication is whether or not it is coming from the same anonymous source -- not that that source is actually named John Doe or that he lives in Detroit. Note that in this case, I don't care at all whether the information in the DNS database is verifiable by a third party -- only that it is the same between accesses to the same site.

That's a different situation from when I want to talk to my bank. My bank is a "real world" organization: it has access to my financial information and I communicate with them (indeed first communicated with them) in person. So, of course I want to know that the online service I'm connecting to is actually run by that bank. ISTM that this particular case is the use-case for CAs: I want a third party reassurance that this URL really belongs to my real bank.

The application for self-signed certificates is more like the former "Seekret" situation. When I talk to Sourceforge, for instance, I just want to know that I'm accessing the real software repository. I don't actually care who owns or operates Sourceforge (in fact SF uses a CA, so I'm really thinking of a much smaller service, but nevermind). Most of the time, I just don't want my passwords to be sent clear text over the internet -- so all I really want to be sure of is that I'm talking to the same site from one HTTP request to the next.

Another thing to think about is value. Why would someone want to break my trust? In the case of a bank account it's obvious -- they can get direct monetary benefit from it. It's much less obvious why they would want to impersonate me or my website: oh there might be reasons -- a prank, injecting bad code, impersonating a user on a forum, etc. But those aren't very strong reasons, and hence it's unlikely that the attacker will go to great expense or effort to do it.

IOW, there's a huge difference between a vault where you store priceless treasure (valuable to anyone) and a privacy lock on your diary (valuable mainly to you). Sure, some hateful person might want to use your diary entries against you, but they're just not going to be as motivated as a professional thief.

After all, there is no security or lock that cannot be broken, given enough desire to break it. So all you're really trying to do is make it hard enough to discourage the sort of attack you expect based on the value of what is protected.

So the question here is: Is a DNS-based signature sufficient as a "privacy lock", and is it a suitable alternative to CA-based security for sites that don't need extreme or real-world based trust?

I must confess that I'm not certain, because I don't understand all of the technical issues. I don't fully understand how easy it is to inject a false DNS report, for example. As it is, however, I frequently accept unsigned/self-signed certificates for low-security sites right now. Would the DNS approach make that more secure than what I'm doing now?

Ryan Cartwright's picture

As it is, however, I frequently accept unsigned/self-signed certificates for low-security sites right now. Would the DNS approach make that more secure than what I’m doing now?

That's my question too. I'm equally not an expert at DNS but it does strike me there are essentially two cases where certificates are needed as you describe them. My idea is not meant to replace CAs but replace self-signed certificates. CAs have their place but not for all cases.

dashcvajksdvh's picture

StartSSL is pretty useless given that its CA isn't trusted by Internet Explorer (or indeed, any other Microsoft product, which uses the PC's certificate store for this purpose). I wouldn't use a free certificate with them for this reason, and I certainly wouldn't waste my money paying for one. They hardly make this clear on their website either. What a ripoff!

FunkyRes's picture
Submitted by FunkyRes on

Note that "Several CAs accepted by all major browsers sell certificates for less than $20/yr, and StartSSL, in the Firefox 3 root store, offers them for free." So the financial complaint should be disregarded.

I looked at StartSSL. First visit to their web site, and I could not access content because I had JavaScript disabled. After temporarily white listing them, their site gave me errors stating they could not find the document I requested. Note that this was the index page - seems they want some kind of http get variable in the string. Not very impressive.

Furthermore, nothing is ever really free. They wanted full name, address, and phone number. I don't want their adds for their commercial products sent to me.

Furthermore, their cert is only good for a year. All I need ssl for is user login. Why should I have to get a new cert every year just to allow encryption of login username and password?

With respect to "man in the middle attack" - that seems far more likely with a real certificate that expires in a year. You see, after the cert expires, the browser doesn't have a problem accepting a new one. With self signed, I can provide a long cert lifetime. Once the user accepts it, if they ever get a different cert from a man in the middle, they should get a warning - just like the OpenSSH warning you get when you try to ssh into a box that regenerated their key. No certificate authorities are needed for ssh, btw ...

Mozilla really should look at how Opera does it. Temporary accept just requires a click. Permanent accept requires clicking the security tab, checking a box, and then a click.

Fast and painless, no un-necessary over the top scary warning.

Author information

Ryan Cartwright's picture


Ryan Cartwright heads up Equitas IT Solutions who offer fair, quality and free software based solutions to the voluntary and community (non-profit) and SME sectors in the UK. He is a long-term free software user, developer and advocate. You can find him on Twitter and