9

FORGE

turns into a shorter distance when you increase the
density of the material. Thin plastic is fine, paper or
card works well, and Perspex about 3 mm deep will
still work. This author made a mistake when first
embedding them in resin to make jewellery, and
put one below a rather chunky ‘gem’ (OK, plastic). I
couldn’t then get the tag close enough to the reader
to use it without taking the ring off!

CAN YOU PROTECT THE DATA?
Yes... and no. You may have seen RFID blocking
wallets, which are basically a mesh or metallic
pocket that your bank card goes in, preventing the
tag from being read. NFC was developed to be a
freely readable data storage method, and so tags

are generally only write-protected. If you pull a tag
out of some packaging (this author got one off her
eyeliner; makeup uses them a lot), you should be able
to read it (a boring inventory number in this case) but
not write something new to it. However, some tags
have a unique identifier (UID) built in to the tag itself
(in those memory blocks you can’t write to) so even
if you cloned the data onto a new tag, it would have
a different identifier. That said, if you got hold of the

original tag you could theoretically clone the UID onto

a tag without an existing UID, but you’d have to clone

one tag at a time, which puts people off.

More advanced (and therefore more expensive)

tags like the Mifare DESFire series are used in things

like transport cards that you can top up and use the

balance to travel. They can encrypt the data so they

wait for a key from the reader, send their own key

back, and the reader is then ‘allowed’ to access certain

parts of the data.

In short, the security of them relies on you being

aware of readers around you and keeping far enough

away not to be read, which is usually around 10 cm,

but we are aware of research into a reader that can be

used from 80 cm away.

And finally, when we were asking around for

projects people had used NFC on, we were impressed

by one: at the Ministry of Defence they use tiny little

NFC tags to keep track of their inventory... of tanks.

NFC was developed to

be a freely readable data

storage method, and so

tags are generally only

write‑protected

”

”

Figure 1

This is the simplest of

NFC examples – just

wire and an LED

Below

This jewellery was

made to store secret

messages in – bring

the pendant close to

an NFC reader such

as a phone and the

hidden message will

appear on the screen