finish bios hackers and forgotten passwords! Here is a solution to protect your PC against unwanted visits. The key, as we describe in this article prohibits the use of your computer using a card reader controlling the electronic machine. Only the owners or recognized by the card reader can access your data.
Subtract the contents of his computer to prying eyes during his absence seems be a major concern for all those who use it in a public place, like the desktop, for example.
If you are in this case, the only truly reliable solution is to install directly on your computer, a physical key (we say "hard", like a software key that you say "soft") capable of ensuring full protection of your data.
You, of course, the possibility of locking your PC in a closet! More seriously, a card system, controlling the electronic computer, you will ensure a good level of security while remaining easy to implementation and use.
I protects you protect yourself ...
As we have seen in a previous article, the magnetic cards can be made all the sauces! One might consider the protection of our computer this way. Here, for reasons of simplicity and compactness, it is a smart card that we use. Go buy a bigger card holder, we have other projects in our boxes! Most operating systems provide the ability to protect the privacy of his computer with a password (Password). This keyword is entered by the user, the software of the computer which stores it.
Thereafter, whenever the computer boots, will claim the password after the test phases performed by the BIOS (basic program from the EEPROM). Alas, and justly, the password is "soft." This means that any small malignant may just gifted, digging well, finding the key (some journals provide everything you need to do this), and "Craker" your protection. Do not talk about that users write their passwords on a "post-it stuck to the screen (If ...), nor of those who have changed the night and the next morning, do not remember anymore!
The operation of the protection system
protection device that we propose in this article affects the "hardware" (physical) of our computer. The printed circuit on the smart card reader is attached to the back of an unused plastic covers the front of the camera.
In this cache, we will take a slot for passage of the card.
The release of our electronic circuit causes the permanent boot the computer, making unauthorized use impossible. The key to switching off the system initialization command is a permanent smart card-like very common credit cards. The card reader used in our project is SLE4404 at Siemens. Let us now
a look at this circuit security system to better understand its operating principle.
As we have said, our electronics assembly keeps in constant contact the initialization circuit that prevents the computer, in turn, starting the processor.
The menu, with its chip interrupts the blockage and allows operation normal until the next start the computer. In practice, the card must be inserted in the reader that the time required for the computer to start. Once the processor is running, it can (should) be removed without consequences.
diagram description of the key
Consider the logic circuit diagram shown in figure 1.
As you can easily see by looking at this diagram, the heart of our welfare system is a PIC16C56 microcontroller (U3), programmed to interact with the card reader via a dedicated connector on the circuit. The integrated U3 is capable of reading the card code and compare it with all the codes pre-stored in memory. If the microcontroller is a correspondence between these codes, the initialization circuit of the computer is automatically released.
Figure 1: Diagram of the key to computer. analysis chart of the program MF 102
Let an analysis of block diagram (Figure 2) program (MF102), included in the integrated circuit U3, to better understand the data management within microcontroller.
Then, based on this information, we can examine what is happening on the circuit.
At power up the system, the microcontroller, initialized by the circuit realized between R2 and C2, planning its own I / O (input / output). Pins 1 and 18 are used as inputs while pins 2, 9, 10, 11, 12 and 17 operate as outputs.
Pin 8 is bidirectional as it charged to exchange data with the key.
Once all the functions, the microcontroller's pin 2 is at logic 1 and feeds the transistor T1 line that connects the initialization (reset) the computer grounded.
This condition remains unchanged until the deactivation caused by the introduction of the card including the possible presence is constantly checked by the reader. If missing, the program is on hold while if it is inserted, the microcontroller checks the status of the rider DS1, so the logic level of the pin 1.
Figure 2: Program included in the PIC16C56 microcontroller. functions DS1 DS1
When opened, the program follows its normal course, that is to say, he reads the code stored in the EEPROM of a chip card.
It should be noted that at the time of purchase, the card has no code while the PIC16C56, it is supplied already programmed in memory and contains a number of 12-bit non-modifiable code that represents the unique key for each microcontroller.
When DS1 is closed, the integrated U3 starts the subroutine programming the EEPROM a card.
After installing the key into the computer, this operation must be performed for each card key. In practice, the microcontroller reads his own code inside PROM and sends it via the pin 8, to map where it is stored in the EEPROM 1.
Once this is complete, the green LED LD1 lights and switches the pin 17 to logic 0 to confirm the end of the registration card. At the opening of
DS1 jumper, pin 2 of U3 returns to logic 0.
Thus, the transistor T1 being more excited he authorizes the release of the line boot that allows the computer starts.
Normal operation of the circuit
Returning for a moment on the normal operation of our circuit, that is to say when, at startup, the microcontroller is open jumper DS1: U3 reads the contents of an EEPROM of the card and, via pin 8, important data on these 12 bits in the first part of this memory. Then, the microprocessor compares these data with those included in the PROM, and if they match, it unlocks the computer by passing the pin 2 to logic 0. Otherwise, nothing happens and the program is ready for a new audit until a card with the correct code is inserted into the drive.
Back to the wiring diagram
Arrived At this point, transfer the concepts that we just acquired in the wiring diagram of our device.
The operating voltage of 12 V is supplied directly by the internal power of the computer. Fuse FUS provides protection against possible improper installation of the circuit.
The microcontroller is powered by a voltage of 5 V provided by the integrated circuit regulator U1.
The reader, it works with a voltage of 12 V connected to its pin 2 (MEMORY CARD), voltage supplied directly by the computer.
When the card is inserted, an electrode present on the latter causes the closure of two switches inside the drive. The 12 volts then come on pin 1 of the reader, thus fueling the transistor T2 and the integrated circuit regulator U2.
Pin 18 of U3 goes to logic 1. This change of state is interpreted by the microcontroller as a card insertion and causes the sequence of phases described above. The integrated circuit U2 is encapsulated in a 7805 TO-92 package. It powers the chip card via pin 3 of the reader and the resistor R11 (which provides protection against accidental contact of +5 V with other tracks on the microcontroller).
Note: Note that the strap 1 is not used in our application.
pins 5-10 on the player are used by the microcontroller to manage the microcircuit card key: Pin 5 is the "reset" RST (reset), Pin 7 is the "clock" CLK (clock), the spindle 8 is the channel bidirectional input / output data pin 9 is the contact T, the pin 10 is the contact P. The pin 6 is not used in our application.
The microcontroller operates with a stable clock provided by the quartz Q1 and by the compensation circuit formed by C5 and C6. The control output of the line initialization the computer is pin 2, while the output for the management of signaling devices is pin 17.
Figure 3: PCB of the key to scale 1. 
Figure 4: Implementation plan components. Iist
R1: 470 Ω 1 / 4 W R2
: 47 kilohm 1 / 4 W R3
: 10 kW 1 / 4 W R4
: 10 kW 1 / 4 W R5
: 15 1 kΩ / 4 W R6
: 100 kΩ 1 / 4 W R7
: 33 kΩ 1 / 4 R8
W: 27 kΩ 1 / 4 W R9
: 10 kW 1 / 4 W R10
: 2.2 MΩ 1 / 4 W
R11: 47 Ω 1 / 4 W R12
: 1 kilohm 1 / 4 W
R13: 100 kΩ 1 / 4 W R14
: 1 kilohm 1 / 4 W R15
: 1 kilohm 1 / 4 W R16
: 1 kilohm 1 / 4 W
R17: 1 kilohm 1 / 4 W R18
: 10 kW 1 / 4 W
C1: 100 uF 25V electr.
C2: 2.2 uF 100 V electr.
C3: 220 nF multilayer
C4: 220 uF 25V electr.
C5: 15 pF ceram.
C6: 15 pF ceram.
D1: 1N4148
D2: 1N4002
T1: BC547
T2: BC547
U1: 7805
U2: 78L05
U3: PIC16C56-HS (MF102)
Q1: Quartz 8 MHz
LD1: LED green
RL1: Miniature Relay 12 V, 1 position
Miscellaneous:
- Jumper to DS1
- Fuse
- Connector Memory Card (reader)
- Support 2 x 9 pin
- PCB ref. H033
Figure 5: Pin Configuration PIC16C56-HS. 
Figure 6: Hole pattern cache. 
view of the plate mounted on the cache recovered. Mounting the circuit on the key
the printed circuit (given the scale 1, Figure 3), install the resistors, diodes, capacitors and support for the microcontroller.
Then mount the transistors T1 and T2 and the two integrated circuit regulators, carefully observing their orientations. Insert and solder the jumper DS1, the fuse holder for printed circuit board, the 8 MHz crystal, the reader (Memory Card) and miniature relay.
Once all welds are complete, insert in their respective brackets, fuse and integrated circuit (U3), being careful to position the keyed-notch as shown in the diagram board layout. The PIC16C56 microcontroller
comes with its embedded program MF102.
installation in the computer
The key installation in the computer must be made machine off, of course! Start by unplugging the power cord 220V sector and open the case of your PC.
Place a plastic covers on the front where you need to practice at center, a slit 60 mm long and 5 mm wide for inserting the key card (see Figure 6). On either side of the slot, 39 mm from the center, drill two holes 3 mm in diameter. On the left of the cache, to 55 mm from the center, make a hole 5 mm in diameter for receiving the LED. With the help of two squares and their screws, attach the lid to the circuit so that the slot is properly aligned with the card reader. The entrance to the drive by 55 mm there is sufficient margin.
Replace the cover on the front of the computer. Without logging in, feed and turn on the PC and then look at using a multimeter, many still made in the water supply available in your machine, a voltage of 12 volts. Shut down the computer and unplug it again in the sector. Cut both son feed that interest you (a +12 V and 1 to 12 V) and connect them (the polarity) on the terminal at 6 locations Our circuit key.
Locate pin reset button on the computer which should be connected in parallel, the normally open relay protection circuit (RESET locations on the terminal).
Finally, connect the LED circuit terminal block also key and verify the closure of the rider DS1.
Using the smart card
The key to our safety device is a smart card type SLE4404 at Siemens. This is an integrated circuit with a 416 bit memory organized into blocks that are accessed through one or several codes.
In our case, we use only the simplest part of the circuit, that is to say the EEPROM 1.
In practice, the unlock code is stored in the first 12 bits of the EEPROM SLE4404.
In the reference table (Table 1), we see that it is possible to write data into the EEPROM 1 without having to enter an access code. By cons, a code is essential when it comes to pass to logic 1 every bit map to delete its contents.
In our application, the controller is limited to reading and writing its own code.
In other words, a write command to the EEPROM chip to 1 part of the card as a message series with the hex address 49. The 12-bit ID code, divided into groups of 4 bits, complete the statement. The message starts with STX (start), followed by 49H and the three hex values each consisting of 4 bits. These three represent the latest information in the order, benefits from 84 to 87 (84 is the first bit), those 88 to 91 and from 92 to 95 (95 is the last of the 12-bit). The message ends with ETX (end).
In the identification phase of the map, queries the microcontroller chip on its content through another command: STX, followed by the hexadecimal value 4A and finally by ETX.
map, in turn, responds with STX followed by the three groups of 4 bits and the ETX-end message.
The initialization process data stored on an EEPROM of the card is possible but it is not supported by the program we have.
Table 1: Structure of the EEPROM of the Siemens SLE4404. We use in our application, the EEPROM-1 block. Implementation of the key
boot, the relay of the key card glue. The computer then sees his RESET to ground and gets stuck. By inserting a blank card inside the reader, the subroutine program MF102 copy the code on an EEPROM of the card. Now you can open jumper DS1 and if everything was done correctly, the computer will start without any problem after releasing the RESET!
If you are unsure about your installation (it always has and if it does not, it would be better to have), you can test it on your timeline. On
release "- + V" terminal block, connect a power supply 12 V (always the polarities), and the RESET output, connect a multimeter, preferably needle-set size on the 100k ohm ½. Turn and practice as explained before. When the meter indicates
continuity, it simulates the lock reset the computer and vice versa.
Enter the card once programmed and see the operation. It must, of course, cut and put food before each introduction of the map to simulate the extinction and turned on the computer.
0 comments:
Post a Comment