self-signed certificate : Java Glossary

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certificate  self-signed certificate
aka free, phony code-signing certificates.
Code signed by a real real certificate gives you strong assurance that code was written by whom it claims to be and that no one has tampered with it since.

Code signed with a phony certificate does not even guarantee that no one has tampered with the software since the original, effectively anonymous, author wrote it, since someone else could have re-signed it with a different phony certificate.

Do you have to buy a digital certificate to let Applets bypass security? Yes and no. You can create yourself a free phony certificate with Keytool, or analogous tool for other types of certificate. It lets you run the signed Applet. However, anyone can make a phony certificate with your name on it. It is marked as self-issued, rather than vouched for by Verisign or Thawte. Users out in the world would/should refuse to grant your Applet special privilege, since there is no guarantee you actually wrote the Applet and that it has not been tampered with. However, a phony certificate is useful for debugging while you await your real certificate to arrive — which can take months of farting about.

The hassle with using phony certificates is that they must be manually pre-installed on all the client’s machines before your signed Applets will be recognised. With real certificates, that step is not necessary. The built-in signing authority root certificate suffices. It is pretty awkward to pre-install certificates for the general public. Phony certificates are more feasible for strictly in-house use.

In theory, a self-signed certificate should suffice to authenticate code on your own website. Who else could have created the certificate? The need for validation only really comes into play verifying code floating about the net purportedly from you. A real certificate allows that verification, even without checking in any way with your website. In contrast, a digital signature with a phony certificate proves absolutely nothing.

Most users don’t understand even the most basic facts about certificates. They are thus overly frightened of self-signed certificates. So you will likely end up buying a real one eventually.

See keytool for details of how to create a phony certificate.

To create phony SMIME email authentication certificates in Windows use:

Why You Want A Real Certificate

Starting with Java 1.4.1 the status of phony certificates has been elevated. The user is merely warned if a copy of your phony certificate is not in his cacerts. file. Previously you had to find some way to get it there; now it is merely desirable to do so.

Limitation of Real Certificates

Even if you buy a real certificate, your clients will still have to OK your signed Applet to run. Why is this? Let’s say your signed Applet rummages around the hard disk looking for thumbnail photos and uploads them to a server. You need the client’s explicit permission to do something invasive like that, not just $350.00 USD for a certificate.

Terminology: Phony or Self-Signed?

I prefer to use the openly pejorative term phony, where others prefer self-signed certificate. I do this to make people realise that a such a certificate is not really a certificate at all, but a kludge to bypass the security mechanism for those who cannot afford a real certificate. Casual users have almost no understanding them certificates. We need an emotion-laden term to help casual users understand that self-signed code offers almost no degree of safety. Phony certificates are in nowhere near the same league as real certificates.

A real certificate involves three levels of certification.

  1. the vendor certifies he did indeed write the software.
  2. the certificate vendor certifies that the vendor presented identification details to obtain the certificate he used to sign the program.
  3. Sun, for Java code signing certifies (or the browser maker for SSL certificates), certifies that the certificate vendor is a reputable company who takes sufficient care in handing out certificates to software vendors. It indicates this certification by including the public root certificate of respected vendors in cacerts..
In contrast, a phony certificate certifies that the holder of certificate he concocted himself did indeed write the software. It says nothing about the identity of the vendor.

The Concise Oxford English Dictionary Luxury Edition defines certificate as an official document attesting or recording of a particular fact or event, the level of achievement or the fulfillment of a legal achievement.

So it seems to me, there no official document involved with a phony cert. A phony cert is almost like a phony degree hanging on the wall attesting to have completed a course of study at a non-existent university. It can be used to deceive the unwary. A phony certificate is not actually a certificate in the Oxford sense. In contrast, the term self-signed sounds completely legitimate, except for a faint whiff of self-gratification. However, it is not completely valueless. For example, I post the public key of my phony certificate on People can then know whoever created also vouches for the signed code posted there, but they knew that anyway, without the signing. It does, however, let people who pick up code elsewhere to know that also if they check the posted root certificate, which is highly unlikely.

I expect, eventually, personal identification cards will be based on private keys. You will then be able effectively to use your birth certificate/planetary ID for all manner of purposes, including purchasing goods and signing code. Then there would be no need for unsigned code or code signed with phony certificates. I doubt the law will continue to protect the right of criminals to harm others anonymously, even if it makes it more difficult for people to perform legitimate deeds anonymously.

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