cryptography

Android requires developers to sign their applications with a digital certificate and that each future release be signed with the same certificate.

Sadly, bad things happen when the developer (you) looses access to the certificate : he (you) will not be able to release updates for the application without it. Never. Ever.

Android does not currently support multiple certificates per application so the best you could do would be to release a new app with the same name, in the hope your users will find a way to it by themselves.

As years go on, you will change your computer, wipe USB keys, reinstall OS, ...
So many dangerous operations for your digital certificates, hidden among millions of files !
If, like me, you are anxious at the idea of losing your certificates or passwords, just print a paper copy !
Although it is not invulnerable, paper should be less prone to mass erasing than a simple electronic file.

The idea is simple, not new, and you just need to know two commands to get a printable hard copy of your certificate.

Let's start.

I was just trying to implement client and server authentication over SSL on IBM Websphere 6 (JRE 1.4.2)...

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It may sound awkward in 2012, but if you wish the HTTPS server to identify your Java client (versus : only the server is identified), you will have to write your own implementation of a socket factory.

The Java Runtime Environment doesn't provide ready-to-use classes to do this. Yes : there is javax.net.ssl.SSLSocketFactory.getDefault() but it requires to set some system (therefore global) properties to point to the certificates files !!!

Even with Apache's HttpClient (at least version 3.x), you have to use a custom SSLProtocolSocketFactory.

The HttpClient SSL Guide provides sample code to implement mutual client and server authentication ; unfortunately the latest stable release of it (contrib 3.1) is bound to Sun's API with imports such as com.sun.net.ssl.KeyManagerFactory. Needless to say that this will not work on an IBM Websphere JRE...

This article contains an implementation of a SSLProtocolSocketFactory for HttpClient, to whom may be interested...