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#1 2015-06-18 09:14:03
- kat6877
- Member
- Registered: 2015-06-18
- Posts: 2
Mifre classic with honeywell reader
Hi All,
I am doing configuration mifare classic 4k (blank china card) with honeywell reader.
When I scan with the reader,the card number is showing as 39942. I can add the card and use it.
But when I scan with mifare tool on my NFC mobile ,the card UID is 06:9C:0F:C5.I do not see any number related to 39942 in all sector.
So this 39942 has been stored in which location? And how can I change it with different new number?
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#2 2015-06-18 16:12:10
- jump
- Contributor
- Registered: 2015-04-29
- Posts: 57
Re: Mifre classic with honeywell reader
$ printf "%x" 39942
9c06
So your reader is only using the first two bytes of the UID
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#3 2015-06-19 09:03:39
- kat6877
- Member
- Registered: 2015-06-18
- Posts: 2
Re: Mifre classic with honeywell reader
So normally the reader should read 4 bytes?
What is the disadvantage of only 2 byte?
How can I fix to have more security?
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#4 2015-06-19 11:44:38
- jump
- Contributor
- Registered: 2015-04-29
- Posts: 57
Re: Mifre classic with honeywell reader
I don't know what your reader is supposed to do 
From my point of view, no decent security system should rely exclusively on the UID of a tag because of collisions and one can easily spoof it or harvest them (the UID is public information).
The immediate consequence of using 2 bytes instead of for is that you divide the security by 65536 basically. Instead of having 4 million possibilities, you lowered it down to 65536 cards. Therefore the odds to get a collision here (2 different badges seen as the same by the system) are pretty high.
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