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Weekly Report

16

Jul

2015

I got AES going! 802.15.4 uses the CCM* block cipher mode with AES as the cipher (using 128bit keys).

This was really difficult! Small changes in the input resulted in wild changes in the output (as you would expect!). I wrote a tool with libtomcrypt to create some reference data (something that I would then try to replicate with the CC2538 libraries). In the end, I managed to make this work.

I also got this going with Wireshark (which highlighted an endianness issue with my libtomcrypt tool). Wireshark will now accept my AES encrypted messages which gives me confidence that the implementation is correct.

The implementation is a bit hacked together at the moment (as I was hacking about to get it going) however tidying it up should be simple. Then I can move on to decryption.

As for the security, I have no idea how well this implementation would perform against side-band power analysis attacks. This is something I'm not even going to consider trying to defend against at this stage! In the future, however, this might be important.