The Untrustworthiness of Self-Signed Certificates

By Larry Seltzer  |  Posted 2008-08-20 Email Print this article Print

SSL pages with self-signed certificates are less trustworthy. But does Mozilla's Firefox go overboard with this issue? Making the Web "safe by default," Web browsers are suspicious of SSL Web sites (those that use an https:// prefix) that use certificates not signed by a trusted certificate authority, such as VeriSign, GlobalSign, GoDaddy or Thawte. Firefox 3 in particular makes you jump through hoops in order to view such a page. This has caused some in the Web security community to question the importance of the SSL authentication.

User interface changes in some newer browsers have gotten some in the security community riled up. The issue is self-signed certificates. Some folks don't like users being told that their roll-your-own certificates aren't as good as the non-free ones. But the fact is that they aren't as good, especially when the overall population of users of web browsers is considered.

The https:// in a web address means that the web server has an SSL digital certificate, and this does 2 things for you. First, communications between you and the web server are encrypted (the certificate is used to construct the private key for the encryption). Second, the certificate contains an identity which is presented to the browser user; the user can look at this identity and decide if it is the right one for the web site and if it is trustworthy.

Browsers And Unsigned Certificates. Click here read more.

The tools to make these certificates are free and anyone can make a certificate that says they are "Citicorp, Inc. New York, NY", so how are you supposed to know the difference? The answer is in trusted certificate authorities. Web browsers (and other software, such as Windows itself) come with embedded lists of these trusted CAs and their public keys. The idea is that these CAs, before they issue a certificate to an entity, check to see if that entity is in fact the company or individual it purports to be. Thus the CA is vouching for the identity of the holder of the certificate

When a certificate comes along the browser sees if it was signed by, and therefore issued by, one of the trusted CAs. If it is, then things are cool. If not, then nobody is vouching for the identity. Because the Internet is full of lying, thieving no-goodniks browser authors have decided that such certificates deserve a special level of scrutiny.

Internet Explorer 7 and Opera 9.51 both react to such a page with a warning that the page's certificate is not quite right and that such a certificate is sometimes used by malicious pages in order to trick the user. They ask if you want to continue and, if you do, you are allowed to go to the page. Internet Explorer makes the address bar red for the page and puts "Certificate Error" in the right-hand part of it.

Firefox, on the other hand, shows a much more urgent warning with much more technical stuff thrown at the user. If the user wishes to go on to the web page they can't just go there, they first have to create an exception rule, a multi-step process which includes many more warnings.

For a demonstration of how this works in the 3 web browsers see our Slide Show: Browsers And Unsigned Certificates.

Larry Seltzer has been writing software for and English about computers ever since—,much to his own amazement—,he graduated from the University of Pennsylvania in 1983.

He was one of the authors of NPL and NPL-R, fourth-generation languages for microcomputers by the now-defunct DeskTop Software Corporation. (Larry is sad to find absolutely no hits on any of these +products on Google.) His work at Desktop Software included programming the UCSD p-System, a virtual machine-based operating system with portable binaries that pre-dated Java by more than 10 years.

For several years, he wrote corporate software for Mathematica Policy Research (they're still in business!) and Chase Econometrics (not so lucky) before being forcibly thrown into the consulting market. He bummed around the Philadelphia consulting and contract-programming scenes for a year or two before taking a job at NSTL (National Software Testing Labs) developing product tests and managing contract testing for the computer industry, governments and publication.

In 1991 Larry moved to Massachusetts to become Technical Director of PC Week Labs (now eWeek Labs). He moved within Ziff Davis to New York in 1994 to run testing at Windows Sources. In 1995, he became Technical Director for Internet product testing at PC Magazine and stayed there till 1998.

Since then, he has been writing for numerous other publications, including Fortune Small Business, Windows 2000 Magazine (now Windows and .NET Magazine), ZDNet and Sam Whitmore's Media Survey.

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