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#1 2014-05-01 15:37:43

marshmellow
Contributor
From: US
Registered: 2013-06-10
Posts: 2,302

Another EM4xxx format?

I have the following 3 cards that are identified as an EM41xx format by the proxmark.  it appears the printed values are encrypted so as to be difficult to guess the next number.

Printed # - Chip ID    - Printed to Hex:
25919337  - 010D774169 - 018B7F69

It appears the beginning "01" and ending 2 digits are a direct transfer from the chip ID.
the printed number has a sequence in the first for digits of the decimal number.

My guess is the digits 5&6 of the chip id correspond to digits 3&4 of the Hex of the Printed card number. also digits 7&8 CID = digits 5&6 of the Hex of the printed #

any thoughts?

Last edited by marshmellow (2014-05-02 18:05:37)

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#2 2014-05-01 17:03:38

carl55
Contributor
From: Arizona USA
Registered: 2010-07-04
Posts: 175

Re: Another EM4xxx format?

There does not appear to be any encryption being used. It is a standard EM410x format.

Per the EM datasheet, the first 8-bits of the Chip ID is the Vendor Code (0x01 in your examples).
The next 8 digits are the card number (e.g. 0x0D774169 in your first example).
The printed number is normally just a decimal version of the card number (e.g. 0x0D774169 = 225919337).

It appears that your printed card number simply truncated the card number by dropping the first digit resulting in 25919337 which is 0x018b7f69 in hex. I suspect that they had a 9-digit limit on the printer field so the first digit was simply not printed.

Last edited by carl55 (2014-05-01 17:09:10)

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#3 2014-05-01 18:11:55

marshmellow
Contributor
From: US
Registered: 2013-06-10
Posts: 2,302

Re: Another EM4xxx format?

wow...  I can't believe I missed that.  sorry.  and Thanks!

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#4 2014-05-01 18:21:26

marshmellow
Contributor
From: US
Registered: 2013-06-10
Posts: 2,302

Re: Another EM4xxx format?

the thing that threw me off is these come with the first 4 digits incrementing and the last 4 appeared random...  I'm going to check to see if any number works in the system or just the specific ones.

Thanks again.

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#5 2014-05-07 18:28:24

blogfish
Contributor
Registered: 2013-06-05
Posts: 17

Re: Another EM4xxx format?

marshmellow, can you send me a private message. I am interested in getting some cards from you. Thanks.

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#6 2014-05-07 18:36:55

marshmellow
Contributor
From: US
Registered: 2013-06-10
Posts: 2,302

Re: Another EM4xxx format?

blogfish wrote:

marshmellow, can you send me a private message. I am interested in getting some cards from you. Thanks.

So far I have been unable to figure out how to private message on this forum.  as an option, my ICQ # is: 6six8fourOO77four

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