[extropy-chat] rfid

[Luke Howison]

RFID tags hold a string of bits called the EPC (electronic product
code).  It isn't 95 digits long, it is 96 *BITS* long.  So all your
calculations were borked, sorry guys.  However, the real story is
still interesting.
The EPC is divided into sections, three of which hold information:

28 bit Manager Class:  unique identifiers for 268 million companies
24 bit Object Class:  16 million (for each company)
36 bit Serial Number:  68 billion (in each class)

Thats a total of 88 bits of useful info, which suggests a total of
3e26 numbers (2^88).

A ridiculously large number, yet apparently it isn't big enough - a
tag with a 256 bit EPC has been proposed:
64 bit Manager Class:  18 quintillion companies (1.8e19)
56 bit Object Class:  72 guadrillion product types (7.2e16)
128 bit Serial Number:  340 undecillion unique product numbers (3.4e38)

Taken together, thats 248 useful info-containing bits which could
identify 4.5e74 objects.  Let me restate that:

450 billion vigintillion objects.

However, its still less than the number of atoms in the universe (more
than 4e79), and quite inadequate for, eg, counting all the neutrinos,
photons, etc.

Also Mike, for the paranoid they are developing RFID blockers, which
would transmit a signal masking particular parts of the EPC. 
Effectively the reader tries to read the number, stumbles, starts
again, and keeps looping, unable to read the whole EPC.

Luke H

Note:  The 256 bit EPC actually has three different proposed section boundaries.
References:
http://www.rfidjournal.com/article/articleview/219
http://www.infomax-usa.com/electronic_product_code.htm
http://en.wikipedia.org/wiki/Names_of_large_numbers