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With ultralightC we could be in situations where read() is called without prior
authentication and AUTH0 < MIFARE_ULTRALIGHT_C_PAGE_COUNT_READ + 1
Several situations may occur:
Let's put auth0 = value of AUTH0 at 0x2A
read(x) with x <= auth0 - 4:
read done properly
read(x) with auth0 - 4 < x < auth0
read result is wrapped
bug in libfreefare: cached pages are not wrapped
e.g. auth0=3, read(0) returns page0|page1|page2|page0
and libfreefare caches wrongly page4 with page0 content
read(x) with x >= auth0
read fails properly
The difficulty to handle those cases, especially the early wrapping, is that
0x2A cannot be read in such situations and must be deduced by trial & error.
E.g. by trying to access the latest cached page, we can see if we get an error
or not and if cache is valid or not.
And probably we need to keep track of two other state values in the cache to
avoid this extra check whenever it's possible:
* latest known valid page
* if we reach 0x2A we can remember its actual value
* if we're authenticated we don't need to check page validity
My proposal:
* use another temp buffer to hold read data
* reduce tag cache buffer to actual max size (today it's hacked =+3 to cope
with wrapped read of last page)
* if (UL or (ULC and AUTHENTICATED)), copy data to cache with proper wrapping
if required
* if (ULC and not AUTHENTICATED), copy one single page in cache and ignore rest
of data
It's less efficient when reading without being authenticated but it keeps the
code much clearer.
What do you think?
Original issue reported on code.google.com by yob...@gmail.com on 15 Jan 2013 at 8:18
The text was updated successfully, but these errors were encountered:
Original issue reported on code.google.com by
yob...@gmail.com
on 15 Jan 2013 at 8:18The text was updated successfully, but these errors were encountered: