Observations of MIFARE Classic 4K Card

Recently I am developing an application for Windows environment with smartcard, and below are some notes I would like to make about MIFARE Classic 4K card:

• Block 0 is not writable. It contains card ID and information stored by manufacturer
• Blocks are divided into sectors, and each sector contains one trailer block
• Trailer block stored keys to authenticate the sector it belongs and attributes which decide access right to the sector
• Handling the trailer block not carefully may lead to all rights to that sector disabled, and I have successfully (or I should say accidentally...) locked the whole sector 0. However, as the GetID command is still functional, that command should be using some other way to read the ID from block 0 / some hidden block?
• As trailer block stores the authentication keys of its sector, updating them means changing the authentication keys. Location of keys: first 6 bytes -> Type A; last 6 bytes: Type B
• Reading/Writing a data block requires authentication beforehand
• Authenticating one block is equivalent to authenticate the whole sector
• Only one sector can be authenticated at any time. E.g. If you authenticate sector 2 after authenticating sector 1, you can now only access sector 2 but not sector 1. In order to access sector 1, you have to authenticate sector 1 again.
• The above does not only apply to one single application. i.e. If application A authenticated sector 1 and then application B authenticate sector 2, application A will not be able to access sector 1 without authenticating sector 1 again.

Using sysinfo in Android NDK

Sometimes you may need to write a program which needs to query some system information (e.g. system uptime). In this case, one may want to call the sysinfo() with struct sysinfo as defined in <sys/sysinfo.h>. Unfortunately, Android NDK does not provide the sysinfo() definition (definition is included since android-9, but I am still having no luck to link it properly). After some searching, I found this thread provides a solution: adding an assembly source (.S). Build it with your project and it works like a charm. The assembly source is attached below for your reference.

STLport in Android NDK r5b

Android NDK includes a special version of STLport since r5, and let developers to use it by specifying a flag in Android.mk files. However, if you are developing using Makefile instead (like I do), using STLport may be a little bit complicated.

First, since the build-standalone-toolchain script of NDK (also included since r5) can only include stdc++ library into the toolchain it builds, compiling with STLport headers may lead to a list of build errors. In order to prevent this, using prebuilt compilers in the NDK ("the hard way" as described in readme) may be a better choice. In this case, you will have to take care with sysroot.

Second, developing with this special STLport has some limitations as mentioned in readme: Exception and RTTI are not supported. Remember to build every cpp source files with -fno-exceptions and -fno-rtti.