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TUCoPS :: Hardware Hacks :: magcard1.txt

The encoding scheme of magnetic cards




From: brian@ucsd.edu (Brian Kantor)
Newsgroups: sci.electronics
Subject: Re: Encoding Scheme of Mag Stripe Cards?
Date: 10 Jan 92 20:58:00 GMT
Organization: The Avant-Garde of the Now, Ltd.

e142-aq@hercules.Berkeley.EDU (Alan Nishioka) writes:

>Does anybody know how information is encoded on the magnetic stripe for
>credit cards, bank cards, my student id, etc.?  Any references?  A trip
>to the library and looking thru the reader 's guide didn't get me anywhere.

Well, there's three tracks (ISO 3554), all 0.110" wide. The top one is
210 BPI and has 7 bits per chr. (incl. parity). Total 79 alpha-num. chrs.
The second track has 75 BPI, 5 bits per chr. (incl. par.) total 40 digits
The third track has agian 210 BPI, 5 bits per chr (yeah incl. par.) total
107 digits.

Data is coded reversing the polarity of the magnetic field once or twice in
the field for that bit. Since you cannot double of half the speed of the card
within the space for 1 bit, it all works.

>I just bought a card reader which had 5 ttl level outputs.  Two for each
>of 2 head tracks and a 5th that goes low when a card is being run thru.
>The chips don't seem to be identifiable.

Well, the bad news is that you'll have to write the decoding software yourself.
Not much to it, I did it on a Commodore-64. Our magazine ("Hack-Tic") printed
the full specs on all this in the last issue.
-- 
Rop Gonggrijp (ropg@ooc.uva.nl) is also editor of  Hack-Tic (hack/phreak mag.)
quote: "We don't care about freedom of the mind, | Postbus 22953    (in DUTCH)
        freedom of signature will do just fine"  | 1100 DL  AMSTERDAM
Any opinions in this posting are wasted on you   | tel: +31 20 6001480



> Article <28174@pasteur.Berkeley.EDU> From: e142-aq@hercules.Berkeley.EDU
> (Alan Nishioka)
>Does anybody know how information is encoded on the magnetic stripe for
>credit cards, bank cards, my student id, etc.?  Any references?  A trip
>to the library and looking thru the reader 's guide didn't get me anywhere.

You'll want to see the American National Standard X4.16 (which I
just happen to have sitting in my lap.)  It is available from the

	American National Standards Institute, Inc.
	1430 Broadway
	New York, NY  10018

My version is dated 1983.  I suspect it has been superceded by now.
It details everything (everything!) you ever could possibly want to
know about mag stripe encoding for financial services cards.

>I just bought a card reader which had 5 ttl level outputs.  Two for each
>of 2 head tracks and a 5th that goes low when a card is being run thru.
>The chips don't seem to be identifiable.

In most all of the MSR's I've taken apart, the chips are custom.
One of our vendor's configurations for the wiring looked like this:

	1	RDT1	Data from track 1
	2	RCL1	Clock from track 1
	3	GND
	4	+5V
	5	n/c
	6	RCL2	Clock from track 2
	7	CLD	Card Presence
	8	RDT2	Data from track 2

You could use a scope to determine which is which -- track 2 is recorded
at 75 bits/inch while track 1 is 210 bits/inch.  Just watch the blinking!
The data is self clocking.

      _____       __    __    _____    __
     |     |_____|  |__|  |__|     |__|  |_____
     ^     ^     ^     ^     ^     ^     ^
        0     0     1     1     0     1     0

>I discovered that cards seem to use two different levels of stripe, for
>a total of 4 tracks on my bank card, but only two on my student id, which
>are at the wrong level for my reader.

Your bank card will typically only use the read-only tracks one and two.
Track 3 is a read/write track that has the same electromagnetic properties
as track 1, but its usage is not standardized within the industry.  Many
cards issued today do not even have magnetic media at the location for
track 3.  (It was originally intended for off-line ATM authorization,
but guess what happened to that idea!)

>The code must be self-clocking and I would guess just have simple 
>error checking (parity) since the card can just be run thru again if
>necessary.

The parity checking is pretty impressive.  Track 1 characters are 6
bits plus one (odd) parity bit.  There is also an LRC (Longitudinal
Redundancy Check) character after the end sentinel character.  The
LRC bits are parity bits for all the characters in the track such
that the total one bits are odd.  (The LRC parity bit is simply a
parity check on the LRC character.)  This scheme protects against
almost all random card damage, as you would have to have four bits
wrong (the corners of a rectangle, physically) to escape detection.
Track 2 parity detection is the same, but track 2 characters are
only 4 bits plus one (odd) parity bit.

The character sets are fairly simple subsets of ASCII.  Tracks 1 & 3
use this table:

		0	1	2	3
	    	00	01	10	11 <-MSD

     0	0000	SP	0	@a	P
     1	0001	!a	1	A	Q
     2	0010	"a	2	B	R
     3	0011	#b	3	C	S
     4	0100	$	4	D	T
     5	0101	%c	5	E	U
     6	0110	&a	6	F	V
     7	0111	'a	7	G	W
     8	1000	(	8	H	X
     9	1001	)	9	I	Y
     A	1010	*a	:a	J	Z
     B	1011	+a	;a	K	[d
     C	1100	,a	<a	L	\d
     D	1101	-	=a	M	]d
     E	1110	.	>a	N	^c
     F	1111	/	?c	O	_d

     a	For the encoding of data on magnetic stripe cards, these
	character positions shall not contain information characters
	(data content).

     b	Optional additional graphic.

     c	These characters shall have the following meaning for this application:
	25  %  represents start sentinel.
	3F  ?  represents end sentinel.
	5E  ^  represents separator.

     d	These character positions are reserved for additional national
	characters when required.  They shall not be used internationally.


Track 1 format:

Format A.  Reserved for proprietary use of card issuer.

Format B.
Start sentinel		1 character
Format code = "B"	1 character - alpha only
Primary Account Number	Up to 19 characters (Note 1)
Separator		1 character
Country code		3 characters (Note 2)
Name			2-26 characters (note 3)
  Surname
  Surname separator="/"
  First name or initial
  Space (when required) (Note 4)
  Middle name or initial
  Period (when followed by title)
  Title (when used)
Separator		1 character
Expiration date or	4 characters or 1 character
  separator		(Note 5)
Discretionary data	The balance to maximum record length
End sentinel		1 character
LRC			1 character (see above for LRC calculation)
Total			79 characters max.

Notes:
     1	In accordance with the account numbering scheme in ANSI X4.13-1983.
     2	When the primary account number commences with major industry
	identifier "5" followed by "9", the encoding of the country
	in this position is mandatory.  In all other situations, the
	expiration date or separator shall immediately follow the
	separator that terminates the primary account number.  The
	country code for the United States is 840.
     3	The absolute minimum data encoded in the name field will be
	a single alpha character in the surname area and the surname
	separator (/).
     4	The space character is required to separate the logical elements
	of the name field other than the surname.  The separator terminating
	the name field should be encoded following the last logical element
	of the name field.  If only the surname is encoded, it will follow
	the surname separator.
     5	In accordance with ANSI X3.30-1971.  If no expiration date is
	associated with the card, a separator shall be encoded.  The
	format for the expiration date is YYMM.

Format Codes C through M.  The format codes are reserved for use by
ANSI Subcommittee X3B10 in connection with other data formats of track 1.

Format Codes N through Z.  Available for use by individual card issuers.


Track 2 uses the following 4 bit character set:

     0	0000	0
     1	0001	1
     2	0010	2
     3	0011	3
     4	0100	4
     5	0101	5
     6	0110	6
     7	0111	7
     8	1000	8
     9	1001	9
     A	1010	Note 1
     B	1011	Start sentinel (start character)
     C	1100	Note 2
     D	1101	Separator
     E	1110	Note 1
     F	1111	End sentinel (stop character)

Notes:
     1	These characters are available for hardware control purposes
	and shall not be used for data content.

     2	This character is reserved for future definition in connection
	with the data format on track 2.

Track 2 format:

Start sentinel		1 character
Primary Account Number	Up to 19 characters (Note 1)
Separator		1 character
Country code		3 characters (Note 2)
Expiration date or	4 characters or 1 character
  separator		(Note 3)
Discretionary data	The balance to maximum record length
End sentinel		1 character
LRC			1 character (see above for LRC calculation)
Total			40 characters max.

Notes:
     1	In accordance with the account numbering scheme in ANSI X4.13-1983.
     2	When the primary account number commences with major industry
	identifier "5" followed by "9", the encoding of the country
	in this position is mandatory.  In all other situations, the
	expiration date or separator shall immediately follow the
	separator that terminates the primary account number.  The
	country code for the United States is 840.
     3	In accordance with ANSI X3.30-1971.  If no expiration date is
	associated with the card, a separator shall be encoded.  The
	format for the expiration date is YYMM.

>BTW, I just want to read, not commit bank fraud :-)  I would have to build
>another card input/output assembly for that :-)

I've seen some scams based on ATM card fraud, but it may be tough to
fool Mother Visa...particularily when you have to hand your card to
a living, breathing human.

Do me a favor and mail me a copy of your interface circuit when you
get it working, OK?

-j, now you know all our little secrets, eh?
-- 
J. Deters                            Ask me about my PS/2.        //
INTERNET:  jad@dayton.DHDSC.MN.ORG   Then,                       //
UUCP:  ...!bungia!dayton!jad         ask me about my Amiga!  \\ //
ICBM:  44^58'36"N by 93^16'12"W                               \X/




Just got my new California driver's license.  No, I'm not 17, but I take the
bus a lot.

It has a holographic plastic laminate of "DMV" and the California Seal.

My color picture was digitized into and IBM computer as was my thumb print
and my signature.  The mag stripe on the back has three tracks.

Just for fun, I thought I'd try to read it.  I had previously been able
to read bank cards (with help from sci.electronics).  I found that the
information encoded is basically just what is printed on the card.  Kinda
uninteresting.  Of course I couldn't figure out what little extra information
was encoded.... (marked unidentified below)

It took me a little while to figure out the format, and I suppose it is
documented somewhere (anyone know where?) but it was fun.

Bank Cards -- conform to ANSI/ISO 7810-1985 ($10)
Track 1:    6 bit word with 1 bit parity.  LSB first.
            code offset 32 below ASCII code.
Track 2:    4 bit word with 1 bit parity.  LSB first.  Numbers only.

Driver's License --
Track 1:    6 bit word with no parity.  Otherwise same as Bank Card.
Track 2:    Same as Bank Card.

California Driver's License:
---------------------------
Track 2:    (low density)
    8 unidentified digits
    License Number
    Separator
    Expiration Date (YYMM)
    Separator
    Date of Birth (YYYYMMDD)

Track 1:    (High density)
DALAN TAKEO NISHIOKA                                       $
974 TULARE AVE               ALBANY       
    Name (58 characters)
    Address (29 characters)
    City (13 characters)

Track 3:    (High density.  Can't reposition read head. );

Great Western Bank ATM Card:
---------------------------
Track 2:
    Account number on the front of the card
    Separator
    Expiration date (no country code)
    Other (propietary) data

Track 1:
    Format B
    Account number
    Separator
    Name (from front of card)
    Separator
    Expiration date (no country code)
    Other data

AT&T Universal Card:
-------------------
Track 1:
    Format B
    Account Number
    Separator
    Name
    Separator
    Expiration Date (YYMM)
    6 Unknown chars
    Calling Card Number (10 digits)

Track 2:
    Account Number
    Separator
    Expiration Date (YYMM)
    3 Unknown chars

Citibank ATM Card:
-----------------
Track 1:
    Format A (proprietary)
    Name
    Separator
    Account Number
    Separator
    Expiration Date (MMYY)
    7 Unidentified chars 

Track 2:
    Account Number
    Separator
    Expiration Date (MMYY)
    7 Unidentified chars

-----------------------------------------------------------------------------
Alan Nishioka      KC6KHV      atn@cory.berkeley.edu      ...!ucbvax!cory!atn
974 Tulare Avenue, Albany CA 94707-2540     37'52N/122'15W    +1 415 526 1818



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