Cellular Network Infrastructure » IMSI Pseudonymization

On Fri, Feb 21, 2020 at 02:33:54PM +0000, osmith [REDMINE] wrote:

I thought that I need to access the filesystem and write it there
(which had me confusing: where to write it exactly? we can't create
new files...).

It may be possible to create new files on some cards under some
circumastances, but in general files are created at personalization
stage. I can personalize sysmoUSIM cards for you with additional files,
if you need it at some point.

But it's much easier:

> static byte[] welcomeMsg = new byte[] { '0', 'x', ' ', 'L', 'U' };
> 

> welcomeMsg[0]++;
> 

Works perfectly, and survives rebooting :)

It's one of the many oddities of the Java environment on smart cards: Any objects
you instantiate are always persistent. So if you want some temporary variables, you have
to actually explicitly allocate buffers/arrays in the heap. It requires serious
re-thinking from other environments.

Also, it is something to consider (not in this context, but in general when writing
such applets) in terms of flash write cycles...