These are too inconvenient. This type of technology is a dead end. These encryption programs come bundled into widely distributed software, including MS Outlook, and the e-mail programs bundled with the newer versions of the Netscape and IE Explorer suites. The notion of unpopularity as a drawback runs though the whole discussion, so it is important to take a closer look at it. This criterion is explained more fully in Chapter 19 of my book, The Complete Internet Handbook for Lawyers .
Unpopular software is harder to use.
It is more difficult to find the keys of those you want to communicate with, and you have fewer options for receiving reliable help when you run into a problem. Finally, unpopular software is riskier. Designing e-mail security products is not at all like designing a word processor, for example. The best short explanation of this is a classic essay by Bruce Schneier, Why Cryptography Is Harder Than It Looks . Schneier is the author of the leading textbook on the subject, Applied Cryptography .