How Do I Crack Satellite and Cable Pay TV? (33c3)

[Music] so coming over to our next talk tonight if you switch off your deck phone and if you're full of different impressions full of different impressions of this day you maybe want to watch TV but it would be cool to have pay TV unencrypted prey TV so Chris Galinski asks himself the same and how to achieve unencrypted pay TV but the hacker way so Chris reverse-engineered nothing less than the signal and the encryption for a standard that remains unequipped it since the late 90s please welcome with an anniversary edition applause Chris kolinsky [Applause] hello everyone my name is Chris Carr linskey I am a hacker from Canada and I'm here today to talk about how I crack digital cable and satellite TV security I studied an access control platform that's widely used across Canada in the USA it's one of the two common platforms that's used in cable TV and it's also used in satellite TV by one of the two Canadian satellite TV operators as far as I know the system has remained secure since it was introduced in the 1990s and I was curious if I could understand the system based on the older set-top boxes some of them are 15 years old and they're still in use so these devices haven't received upgraded security hardware in that time and I started looking at how the system works before I get into the reverse engineering I'll start with a brief description of how digital television is sent over satellite or cable satellite and cable digital television are pretty similar for the most part there are a variety of signal modulations used the relevant ones here are QPSK at about 27 megabits and 8 PSK turbofolk at about thirty eight megabits for satellite and QAM 256 at about thirty eight megabits for cable there's also an out-of-band channel used by cable which is QPSK modulated at two megabits this outa Bantul carries the subscription management program guide information firmware upgrades etc and while you change channels and the cable box Tunes to different frequencies this outer band channel remains tuned so that the Box continuously receives this data no matter what TV channel you are tuned to in the satellite TV this type of data is included within the main transport stream instead of in a secondary out of an transport stream the video is sent as mpeg-2 or h.264 transport stream this is a standard format for carrying video streams so we can be played by any hardware video decoder or a software decoder for example VLC and the encryption system used here is called digisight for two which does not follow the DVB standards that are used in the rest of the world the MPEG transport stream is made up of packets of 188 bytes each packet has a pid' this is used to differentiate different types of data pidz range from zero to x1 f FF each Pig carries an MPEG packetized elementary stream that's a video or audio stream or the pit may carry one or more service information tables the service information tables have an 8-bit table ID and a length of up to a thousand 24 bytes including a CRC 32 for error detection and this table ID identifies the type of data that you can expect within the table table 0 is the program association table containing a list of programs carried in this transport stream and the PMT pit for each program the program association table is always on pit 0 table 2 is the program map table which contains the list of packetize elementary streams and the pit for each as well as an ECM pit there's a program map table for each MPEG program or TV channel that's found in the stream the ECM pit is where entitlement control messages are sent containing information that's used to Det generate the key that decrypts the packetized elementary streams this system uses two types of ECM table 40 I call ECM 40 and table 41 I call ECM 41 on pit one there may be one or more conditional access tables table ID number one these tables identify a pit that carries EMS entitlement management messages these messages are used to set access rights for individual set-top boxes the subscription information like what channels are available is carried inside of EMS this is a hardware interface to receive satellite data Jen picks Skywalker one the dc2 QPSK modulation isn't widely supported in the US v or PCI dvb-s devices and the 8-psk turbofolk modulation support is even less common and one of the devices that does support these signals is this chat Fix device which is using a Broadcom BCM for 500g modulator and it supports both the dc2 QPSK and the 8 PSK modulations it works well the Linux drivers need to be recompiled to include the support for these modes and patches for this we're published by update Lee there's a link on the slide for cable there's a variety of adapters supporting QAM 256 demodulation I use the USB hvr 950 Q tuner unfortunately two to the out-of-band channel is generally not supported by the off-the-shelf interfaces inside the cable box it's handled within the integrated chipset and for the clear QAM consumer devices such as USB interfaces access to the outer band data isn't actually required and so they don't include it inside of the hardware this outer band data is used only for pay-tv services with the satellite and cable interfaces DVB snoop can be used to view a lot of information about the transport stream it's enough information to be quite overwhelming so the trick using it is to being able to sift through the output for the relevant information DVB snoop also doesn't recognize all of the digits i42 tables because it's a non-standard system and DVB snoop is targeted towards the standard systems so DVB snoop may not be able to tell you everything about the transport stream but it was still a very useful tool for all the information that it can provide DVB snoop and most other tools and documentation or deveined designed for the DVD standard or other recognized standards such as atsc digital for cable and satellite systems use a lot of non-standard tables to carry the system information for cable TV some of these tables are standardized by the document SCT e65 there is no BA T or SD T as you'd expect in DVB instead there is a virtual channel table that map's the transport streams and programs to channel numbers the electronic program guide is also not DVD standard so you don't even get the current index program information kind of a standard format another cable TV adapter is the HD homerun prime this one is a network connected three tuner device with cable card support the set-top boxes I studied predate the cable cards although the newer boxes do use the cable cards and they support the digits i42 but cable card support does also mean that this HD homerun prime includes the tuner and kpf QPSK demodulator for the out of an channel so it is able to pass this data to the cable card as necessary however even the HD homerun doesn't make this out of and data available other than the cable card interface so to access the demodulated out of and data I tapped into the HD homerun Prime with a cable card inserted and connected a logic analyzer to the data and clock signals I wrote software using the salia SDK to capture the QPSK demodulated data then in software I perform the interleaving D randomization in the forward error connection and the output is an MPEG transport stream so using an HD homerun prime connected to the logic analyzer connected to the PC running the software the output finally is the 2 megabyte transport stream and this transport stream looks like a standard transport stream and inside are the conditional access management messages program guide information in etc everything that was missing from the main QAM transport stream 2 bits in each packet but will indicate if the packet is scrambled with the even key odd key or not scrambled at all the key is changed at short intervals DVB systems typically would change every five to thirty seconds DC to every 133 milliseconds or one second the key used for decryption alternates between even and odd the odd key is in use while the even key is updated and then the even key is in use while the odd key is updated an encrypted transport stream is sent via the cable or satellite and it's passed through the descrambler in the ACP and the result is a decrypted transport stream that is played by the MPEG decoy the descrambler uses a working key this is a 56 bit desk key that changes every 133 milliseconds or in some cases they have it slowed down to changing every one second this working key is generated by encrypting the frame count from ECM forty packets with the program key the program key again des comes from the ECM forty-one message and is encrypted with a category key the program key is unique to each channel and it changes daily or for every pay-per-view event the category key also des is shared by all the set-top boxes that are authorized for any channel from this provider the category key is sent to each set-top box individually inside the EMM ninety-five message and this category key typically changes monthly but many cable operators change keys much less frequently some of them using the same key for years at a time to decrypt the EMM in order to get the category key seed keys or use each set-top box has a set of 56 bit des seed keys inside of battery-backed Ram these are initialized during manufacturing for the lifetime of the set-top box these keys are used to secure EMS so this forms a chain from the seed keys initialize drug manufacturing and never changing to the decryption of the MPEG transport stream inside a set satellite set-top box we can see the main components of the system the signal enters the tuner and is passed through the demodulator which outputs a serial transport stream this transport stream passes through the ACP access control processor and is then sent to the MPEG decoder to output a video signal to the TV a 68k microcontroller acts as the set-top box main controller it communicates with the MPEG decoder as well as with the ACP laia and spi bus a battery provides backup power to the ACP so it will retain Ram contents even when the set-top box is unplugged there is a TV pass slot near the power supply this is an upgrade slot with a card hedge connector to allow for security upgrades the system stayed secure so the TV pass slot was never used and the newer set-top boxes don't actually include a TV past slot inside so at this point it seems quite unlikely that this TV pass card will ever actually be used inside a cable set-top box it's very similar to a satellite set-top box but the cable box is tend to be more tightly integrated signal enters the tuner and passes through a Broadcom chip that handles demodulation and the same trip will also handle MPEG decoding after the transport stream has been decrypted by the ACP a 68k microcontroller acts as the set-top box main controller again talking the ECP via spi and a battery provides backup power to the ACP and also to the non-volatile Ram used by the main controller a TV pass slot is underneath the mainboard it's not visible in this photo the cable set-top boxes include a second tuner that's used to receive the outer band data this Oda band tuner operates independently of the main tuner and on a separate C frequency range and it's used to provide a transport stream containing the system information with the program guide for more updates emmc etc here we see the ACP chip it's a 100 pin T QFP package from the markings we can see it's a custom system-on-chip made for general instrument corporation g i see all the decryption is performed by the ACP and all the encryption keys are kept only within this chip the newer set-top boxes use newer versions of the ACP I studied the original ACP chip that's seen in this photo as long as the set-top box is using this chip or actively used it remains irrelevant target whether the newer ACPs include more advanced security features or if they exist only for cost savings due to shrinking the die size I don't really know some of the interesting pins on the ACP are labeled here pin 1 is marked at the top left corner of the chip there's an SPI slave controller on pins 1 to 5 used for communication with the set-top box main controller there's a battery backup pin that's connected to a 3 volt battery to keep the RAM contents of the ACP intact at all times there's a serial transport stream input on pin 88 to 92 which receives the data from the demodulator and there's a serial transport stream output on pins 28 to 33 which sends the decrypted transport stream from the MPEG to the MPEG decoder to be output to the TV at one point I had written software for an AVR 32 device not the one that shown here that has a synchronous serial peripheral that supports sending and receiving data at the 27 megabit rate of the transport stream my AVR 32 implementation turned out a bit ugly but rather than cleaning it up I was able to use it as it was it had some limitations like only accepting 64 kilobytes of data for replay logging which was just barely good enough for my studies what the transport stream logging in circuit did show me was that the transport stream passes through the ACP with selected pits being decrypted and then the output is the full transport stream but a selected program has been decrypted the AVR 32 logging interface had rather limited use for me later on when I did more thorough research I did so using an ACP that I'd remove from the box and I put on a breakout board and then I could control the clock and at that point it was much easier to use an X mega AVR platform to send and receive the transport stream through the ACP at a much slower bitrate shown here is the X mega platform I settled on using 4 SPI and also the transport stream interfacing to honor the data pass between the set-top box main controller and the ACP on the SPI bus I use the X mega development board to SPI a ports which acted as slave with the master out slave in signal connected to 1 and master in slave out signal connected to the master out slave in input of the second port so for one port byte sent by the set-top box controller are received from the other port it receives bytes from the ACP in case I want to talk directly to the ACP or the set-top box main controller it's only necessary to connect both the mazi and my so signals on one of the SPI interfaces by holding the main controller in reset my X mega was able to act as the SPI master and then talk to the ACP so this sad talk works for passively monitoring the SPI communications in the set-top box and can also act as the SPI master for indicate interrogating the chip directly by logging the SPI bus between the main controller of the ACP we see that information about the current access levels is sent from the ACP the ACP also receives EMM s via the SPI bus EMM s have been filtered by the unit address number or the set-top box serial number so the ACP only receives messages that are intended for that specific unit command zero four includes the current category key epochs and key selects in use command zero five includes the unit address number command 13 returns the authorized subscription tiers for this unit command seven and eighty-seven provide information about the channel being currently decrypted additionally via the SPI interface the set-top box main controller tells the ACP which pins to decrypt and which is the ECM pit the ACP doesn't send any keys on the bus and it only receives category keys that are encrypted within a MMS via the SPI so all of the really interesting data is contained within the ACP chip itself and it's never sent out on any kind of a bus [Music] so next I started an invasive study of the chip studying it under a microscope the cost of microscopes can range from hundreds of dollars to tens of thousands of dollars or even higher for things like electron microscopes or other specialized equipment though I have a couple of microscopes that I use this one is the meter Toyo FS 7d microscope these meter Toyo are often used for micro probing but you can also use it for other uses for this project I didn't do any micro probing but I used this microscope because it was what I had for studying this kind of technology you could use even more basic equipment but of course if you have the higher-end equipment it's a lot nicer to work with another microscope I use is a Zeiss axial Tron this microscope is designed for inspecting wafers and has really good optical quality I said that more basic equipment could be used and it's true but when you get into this kind of thing you might find yourself again and again investing in more equipment I've about ten thousand dollars in this set up including the microscope and the camera and the scanning stage and other parts to look at the chip under the microscope requires that the chip is D capsulated fuming nitric acid is used for this the chip is immersed in heated red fuming nitric acid which reacts with the plastic packaging and removes removes it the chip is then rinsed in acetone and cleaned with isopropyl alcohol in an ultrasonic bath which leaves the dye bare and clean the nitric acid is quite aggressive and it's important to handle it carefully but the process is really straightforward most people probably wouldn't want to do this in their home so you should go out to the garage and use your fume hood there after the decapsulation the bare chips are left with bonding wires attached to them so these wires will be plucked off using tweezers to get them out of the way already in this photo we can see some of the larger structures on the chip half of it's covered with a metal plane and the other half shows some kind of visible circuitry this is an image of the chip under the microscope it's been stitched together from several smaller images to give an overview of the chip looking at the D capsulated chip we see the bond pads around the outside a metal plate covering the top part of the chip and wires on the bottom of the chip the spaghetti logic running all over the place with a couple of structures that look like they could be a type of memory there's a lot still hidden from us to see more of the chip it will be necessary to Dallaire it to D layer the chip I used hydrofluoric acid to preform a wet etch I use the wink rust stain remover product it's available in hardware stores all over the USA it's a dilute HF solution that works really well for delayering ICS I put a small amount of the wink liquid in a beaker and heat it on the hot plate then I dropped the D capsulated dye in using a pipette I agitate the liquid to disturb the bubbles that form on the surface of the chip so the acid can actually chip more evenly the etching result isn't perfect some parts of the chip will be etched deeper than other parts but I've gotten quite useful results using this technique you really don't want to breathe in these fumes so do this in the fume hood in your garage also after a short time immersed in the heated wing solution the chip was rinsed and put back under the microscope now the top metal plane has been removed so we can see what's below there are some visual effects that we start to see in the photo from the etching being a little bit uneven but overall the dealership looks quite good and is able to start studying it at the top left the tall rectangles are round the four blocks at the top right or ROM and then there's logic that tie these into the logic area below I was interested in finding how the bits were encoded and wrong so I continued delayering the chip this was another dip in the wink and another metal layer has been removed bits in the row were not visible yet so I continued the D layering process at this point we're starting to see more of the visual effects from the uneven etching but it's still not too bad after a third dip in the wink more metal has been removed at this point the D layering is becoming more and more uneven we can see the wrong blocks a bit half etch to a lower layer while half of the upper layers still remaining the wet etching process can be quite difficult to perform completely consistently without adding additional steps such as polishing and at the time I did this project I didn't have the polisher available so I was relying only on the wet etch some of the areas of the ROM are now showing visible bits the other areas haven't been etched deeply enough so I continue to etch further to try and get a clean ROM we can see the wrong bits quite clearly now there are arranged in rows and columns and in this image if a black dot is visible that indicates that the bit is a one image quality is important the better the photographs the more consistently the bits will be visible but it doesn't have to be really perfect you can do some image processing on it you can even repeat the process on multiple chips do you layer them and photograph them and at some point you'll be able to have the entire ROM clean and consistently visible with the visible bits exposed and photographs taken the bits can be extracted using a software image analysis tool or the bits could be extracted manually the ROM here is 32 kilobytes or over 260,000 bits so a manual extraction would be a bit labour a bit labor-intensive but it isn't impossible a software tool is more efficient so I wrote some software to analyze the images in identify the one in zero bits they're a bit smart with a yellow box for zero bits or a blue box for 1 bits I use the software to analyze the image and then I can quickly review the results manually and identify any errors that I can see after extracting the bits from the photographs I have a binary version of the ROM data this is a visual representation of the bits extracted from this piece of ROM the black box to signify one bits and the white boxes signifies 0 bits in this image I've overlaid the extracted bottom 13 rows of bits over the photograph you can see some visual patterns inside this also and these visual patterns are a good indicator that this ROM is probably not scrambled this image was the end of the ROM where you can see a pattern covering most of the image due to a repeated pattern of filler bytes that occupy a new space at the end of the room at the very end of ROM the pattern is interrupted this is where the vectors table exists at the top end of memory indicating the reset address and the addresses of interrupt handlers the ROM has unused space the filler bytes at the end and the vectors table at address is ffff 6 through ffff after extracting the bits and decoding them into bytes the hex dump can be studied there is a copyright 1997 C HC the ASCII string and wrong which is helpful to identify when the ROM has been decoded correctly if you can read the ASCII text and surely the bits are in the correct order the decoding in this case is just a matter of organizing the bits into bytes it's quite straightforward there was no scrambling or anything else that was complex with the ROM contents extracted the software can be disassembled and analyzed the first step was to identify the CPU architecture studying the binary dump it appeared to be an 8-bit CPU but wasn't 8051 or 6c 805 or any other of the processor types I tried first eventually I try disassembling a 6502 in the code made sense later I had remembered that I'd looked at a previous version of the Access Controller from the same manufacturer which was used in another system video cipher - plus an ancestor of digits ifer on the older chip was a copyright notice from WDC who licenses the 6502 core IP it was visible directly on the chip die under the microscope so this would have been a great clue for the CPU architecture if I'd actually notice it earlier for disassembly I used Ida it supports 6502 and is of course a very powerful disassembler in addition to disassembly I use 6502 simulation software to study the software in a virtual CPU the simulation is really helpful when disassembling the software it provides a lot of insight into what's going on since 6502 is a very well-known architecture it was not at all difficult to find an existing simulator even free with source code the 6502 is used in 8-bit computers like the Apple 2 in Commodore 64 so there's really a lot of enthusiasts and a great deal of information about this architecture as I gained understanding of the system on chip through disassembling the software I began adding some of the features into the simulator to emulate some of the hardware peripherals that were found inside the ACP device itself one of the first things I saw in the disassembly was that there are two operating modes during startup values in RAM are checked and if the ACP hasn't been initialized it enters the personalization mode used during manufacturing to assign the unit address and seed keys in normal conditions after the set-top box has left the factory this personalization software is bypassed the ACP will always run its main application the next thing I found was the application wasn't very simple this 6502 actually runs a task switching operating system eight tasks are run supporting decryption of up to two channels at the same time there are two tasks to handle processing of ECM 40 messages and generation of the working keys used to decrypt the transport stream and 2 tasks to handle processing of ECM 41 messages to generate the program keys that are used to process the ECM 41 tasks for handling EMM processing and there is also it has to communicate with the TV pass interface for security upgrades with another task to handle the messages that are coming in over the SPI interface since the ACP is a custom system-on-chip there is no documentation available describing the hardware capabilities so the disassembly was studied and the input-output registers had to be guessed based on the software usage there is an SPI slave for referral for communication with the main controller the SPI peripheral sends and receives data directly to RAM and then a signal is set indicating that transfer has been completed there is a desk crypto peripheral key data and operating mode or set in registers and when the decryption has been complete the result can be read from additional registers there's a transport stream descrambler the working key is set in hardware registers and the descrambler will then output decrypted transport stream on the serial transport stream interface there are paid filters set by the set-top box main controller over the spi bus these filters select which video and audio streams to descramble and which ECM packets should be received by the acp the received ace the received ECMs are placed in round and the 6502 is notified of a new ECM via register bit so at this point I am starting to get an idea of how the system works I've studied the MPEG transport stream and log ECM and EMM data I've logged the SPI bus and understand messages between the set-top box main controller the ACP I was able to extract the entire ROM contents optically and I've disassembled the software and run it in simulation there are some keys that are found in ROM fixed keys which never change and are used when a channel has a free preview weekend or something of this sort any set-top box that has ever had any kind of authorization in the past is allowed to decrypt channels that are encrypted using the fixed key mode so now the focus is on understanding the ECM and EMM algorithms within the rom software at this point I'm still missing some important information from the ACP all the seed keys category keys and program keys exists only within Ram so to decrypt any of the channels not in free preview isn't possible yet at this point the ECM 40 message is used to generate the working key used to descramble the MPEG streams there's a service ID used to identify each channel and a frame count that's used with the program key to calculate the working key the Crypt mode identifies if the channels operating unencrypted with a fixed key or with a normal secure keys which are typically used the frame count is simply a 24 bit counter that increments each time the working key changes there's a byte I've labeled hardware that has one bit set in it this selects a special decryption mode that I'll come back to a little bit later the ECM 41 contains encrypted program key that's needed to correctly decrypt the ECM 40 there's a provider ID that indicates which TV operator subscribers this ECM should be processed by and there's the same service ID that will be found within the ECM 40 messages the category epoch identifies which category key is in use there's also information about how long this program key will be valid for ECM 41 contains one or more subscription tiers that must be found within the customers ACP to allow this message to be processed the subscription tiers are written to the ACP when the EMM containing authorization details is received there is again a hardware crypto select byte that I will get back to this slide shows what a half of a second of ECM forty and ECM forty-one activity might look like to be able to descramble the program the ACP must process a current ECM 41 to get the program key and then process an ECM 40 to get the working key the working key is then used by the descrambler to decrypt MPEG stream until the ACP receives the ECM 41 with the current key as well as an ECM 40 with the frame count it's not yet possible to decrypt the transport stream the working Keys have a short lifetime only 133 milliseconds the series of ECM shown here all would happen within a period of a half of a second the EMM s are split into four parts each part contains a portion of the subscription information for this set-top box a category key is calculated from each of the four parts and the key that is calculated for each part has to match the others or the EMM will be rejected and all authorization and category key will be wiped from this acp when the first EMM part zero is received the authorization data inside the ACP is reset and will be replaced with authorization data from the EMM when the next part part one is received the existing authorization data within the ACP from part zero is hashed along with the data in part one if the result is correct then the authorization from part one is copied into the ACP alongside the existing data from part zero if the result is incorrect then the ACPs authorization is erased in this way the four EMM messages are linked together and if anything is modified within any of the EMM messages the authorization will fail this is an example of an EMM each of the four EMM parts contains some common information like the unit address and which category epoch this EMM contains information for the EMM can contain two category keys one for the current epoch and also for the next so that when there is the change of the category key the ACP already has the next key available to decrypt the category key from the ECM from the EMM the seed keys contained in the ACP are used the seed keys are unique to H ACP and are assigned during manufacturing EMM s are transmitted out-of-band for cable systems but they're passed to the ACP in the same ways for satellite systems so the ACP level there's no difference between the satellite and the cable systems at this point it should be possible to decrypt channels that are using a fixed key mode analysis of the rom has shown the algorithms used to process the ECM and generate a working key the fixed keys are known because they're contained in ROM there could have been some question about the possibility of bit errors from the optical rom extraction process but the fixed keys can be confirmed is correct because the wrong software performs a check some of this 256 byte area that contains the keys successfully running the checksum on the extracted ROM data indicates that the extracted keys seem to be correct but when I attempted to decrypt a fixed key channel there's a problem it did not work whether it was a bug in my decryption implementation or something else was unclear however I had noticed the bit in ECM 40 was set that causes a bit within the ECP hardware peripherals to be set the purpose of the bit was unclear but its address was suspiciously close to the transport stream descrambler key so I start to suspect that there might be some encryption other than just standard des to be able to learn more about the ACP I started to look at glitching leadership if I can succeed to glitch the chip I may be able to find a way to read and even write memory and possibly a way to run my own software directly on the chip this will allow me to control the hardware peripherals and be able to observe the chips operation under different conditions timing tests of the ACP suggests that the 6502 is running from an internal clock source so this ruled out a clock glitch attack a VCC glitch makes sense and with the age of this chip it seemed reasonable to expect that it would be susceptible to VCC glitches the stronger protections against this type of attack are relatively recent my glitcher design is quite simple it's based on an X mega development board and breadboard I use the X mega to communicate with the ACP / SPI and to control the glitch a 74 series 40:53 analog switch is used to quickly switch the ACP VCC between two voltages a normal operating voltage and a lower glitch voltage I use a bench top DC power supply and two outputs so I can easily adjust both the normal VCC and Glitch VCC levels other parts on the breadboard are an oscillator to provide some clock inputs necessary for the ACP to operate and an inverter and NAND gate to cut out the clock during the time of the glitch to simplify the test setup as much as possible the ACP was removed from the set-top box and soldered to a breakout board so in this process the battery back Ram was disconnected and all the keys were lost but for the purpose of developing working glitch this was okay this simple breadboard base glitcher is quite flexible the breadboard can be modified to test different ideas and reconfigure quickly more complex and advanced glitcher wasn't necessary to test the glitcher to find out if it will work and what voltage levels are successful we can send a command to the acp then glitch and then see the response from the acp the general strategy is to lower the voltage just to the point where the chips sometimes resets due to the glitch by adjusting voltage levels in glitch length and timing when the glitch will land like lexically succeeded to cause acp responses to be altered the checksum on spi packets is very convenient when unusual data is received from the acp chip with a valid checksum it's a pretty good sign that the glitch caused the temporary fault within the CPU but that normal operation was resumed depending when the glitch is delivered different effects are seen we can see that generally as the glitch is moved later it's the later bytes of the response packets that change so at this point it looks like the glitcher works and is able to cause a pre fault since I had of glitch I took the circuit from the breadboard and etched a simple PCB that could plug directly on the X mega development board this performs exactly the same function as the breadboard glitcher but I'm a bit less likely to accidentally unplug a wire from the breadboard and have to repair things the circuit was simple enough that I could create a one sided PCB so it was very easy for myself to etch at home now my goal is to have the ACP execute the code of my choice because the 6502 is a von Neumann architecture all code and data memories share the same address space from software disassembly I saw that there didn't appear to be any paging or MMO features the software in ROM is fully self-contained there is no EEPROM and RAM is never used to hold executable code so there aren't jumps into these areas to exploit and in fact it wasn't clear if there's anything preventing code execution outside of wrong I decided to take a chance and test the Fram is executable so I send a message via SPI knowing that this message will be stored in RAM the message contains 6502 executable code that will copy itself to an unused area of RAM execute from this area and send an ACK indicating it was successful because I study the use of the SPI interface in the ROM code I'm able to create this executable payload that will continue to receive commands via SPI after it's taken control of the ACP to try to maximize chances of success I looked through the rom code for multibyte instructions which have broken up would have contained within them a jump-off code with a destination that should lead to where my executable play payload was placed and round since the ACP has a single address space this gives a lot of opportunities for glitching to cause execution to reach the payload there are multiple scenarios possible in addition to my selected glitch target stack corruption is a possibility and really any abnormal program flow has some possibility that it could eventually land in my code the von Neumann architecture without strong memory management is a very fertile ground for glitching anything in RAM potentially could be executed so at this point there are several uncertainties but so far nothing totally rules out the possibility of success the ACP operates from an internal clock source and the in corrupt driven task-switching does add some further timing uncertainty so I will send the code payload delay then glitch and see the result when it's unsuccessful I change the delay and I try again I try to aim for the instruction that I've identified as possibly corruptible into a jump but there are a lot of unknowns so really the process is like fishing throw the line and hope I have a target but no way if I no way to know if I can really hit it or if it will have the expected result but sometimes fishing is good relatively quickly the ACP returns in AK indicating a successful glitch the first successful glitch took some hours to find and then after this it was possible to make it work repeatedly in a matter of minutes or even seconds so now I have my code executing in RAM I'm able to send the ACP additional pieces of code to be executed this allows me to read any memory address write any memory address and perform any other operations possible with the 6502 I wrote a simple application to perform glitch searches and then to interact with the code payload backdoor installed and RAM this program allows me to enter an address in length and have data returned or write to memory etc there's also support for setting the key in data and performing deaths encrypt or decrypt using the desk Hardware that's inside the ACP a few things I noticed at this point there is a 2 kilobyte area of ROM that if I attempted to read it caused the chip to reset this area of ROM contains the personalization routines that are never normally used after the device leaves the factory there's also protection against modifying the seed keys in RAM trying to store a value to these memory locations appear to do nothing there are specific addresses within RAM that can't be read or the chip will lock up these are clever traps put in place as a security measure the 7 byte 56 bit Keys stored in RAM straddle these dead addresses so a potential exploit that could cause a linear dump of memory will be stopped before a complete key is ever read when the chip is reset it means having to glitch in again because my code payload exists only around and there is no way to hook in a permanent backdoor since we can execute code on the ECP receiver response we can read the ROM to have its contents without any of the errors that were introduced during the optical extraction process comparing the results of the optical rom extraction with a proper dump we can see how many errors were in the optical extraction overall the optical extraction was quite good it was after all good enough to understand the software and get us to this point there's only one byte with more than a single incorrectly flipped bit many of the errors that existed were quite obvious when disassembling the software if an instruction is out of place but flipping a single bit would make it sensible then it was probably a bit error I didn't keep detailed records but I think I probably caught about half of the ROM errors during the disassembly process before I started glitching the interesting keys in the ACP are all stored in RAM only this includes working program category and seed keys the RAM is battery backed if the seed keys are ever lost for mam this ACP can no longer process EMM s and so is useless it's possible to glitch the ACP and read memory but the glitcher works on an ACP removed from their set-top box when the ACP is in circuit the cadet the connections to other components and 16 VCC connected pins pose the problem to glitch the ACP in circuit will require some modifications to the set-top box disconnecting the ECP from other parts or another alternative is to remove the ACP from the set-top box and place it on a breakout board without losing the battery power and wiping round rather than modify the set-top box where each of several different models would have required unique modifications I decided to try to remove the ACP with a battery still attached the plan is to carefully lift the battery and ground pins while the set-top box is powered on providing VCC I use a small tool I made from a razor blade using a dremel tool then attach the handle of a screwdriver this tool can be wedged under a pin then with some hot air the solder will melt and a single pin can be lifted straight up without damaging any of the other pins with the pins lifted an external battery can be attached after attaching an external battery [Applause] after attaching an external battery the set-top box is unplugged and the ACP can remove remove from the set-top box using hot air the ACP can be roof from the set-top box glitch and can even be place back in the set-top box if desired to do this I just use hot air and a lot of flux additionally once the interesting keys have been extracted it might not even be necessary to replace the ACP in the set-top box the ACP is now placed on a breakout board and connected to the glitcher not all the pins need to be connected only a handful of fins were actually used by the glitcher you can also see at this point the glitters in a project box the aesthetics greatly improved since the bread box plate the bread board based lecher but the functionality is identical the timing of ACP responses is different on a chip with valid ram compared to the previous chips that I'd glitch before I didn't confirm whether the cause of the timing difference was due to a different oscillator configuration or just a different software path but by adjusting the timing of the glitches the executable code payload runs as it did on the previous chips so now we can read the round contents of a valid ACP including the category keys if the set-top box like current authorization as well as the seed keys that are used by this ACP to decrypt a MMS without eval with a valid category key ECMs can be decrypted and a correct working key can be calculated for any channel now with the capability of running my own code of the ACP it's time to look at the transport stream D scrambling there's a hardware register bit that's set or cleared based on a bite in the ECM 40 when this bit is clear standard desk decryption is used when the bit is set the transport string descrambler acts differently additionally there's an 8 bit hardware register in the DES / if roll area when it's 0 the peripheral operates the standard desk for any other value the peripheral acts differently at this point I started to think I might be looking at doing a gate level reverse engineering of the chip to understand this functionality the chips using technology that's older so reverse engineering should be feasible but if possible I'd like to avoid all this extra work it would be quite time-consuming and might give imperfect results similar to the optical ROM extraction so I start with trying to characterize the scrambling modes the transport stream packet is made up of a four byte header and 23 blocks of 8 bytes each the desk operates on these eight byte 64-bit blocks by flipping one bit and encrypted input ECB CBC or ofb modes can be differentiated flipping one bit causes an 8 byte block to be corrected and the corresponding bit in the following block to be flipped this indicates CBC mode is in use timing of the input compared to the decrypted output was measured with the descrambler and standard s and in the custom hardware mode no timing difference was seen this suggests the internal properties of desks haven't changed which makes sense because the decryption has to be done in real time so this suggests that crypto customizations are not affecting some deaths internals like the number of rounds also by using an ACP as a decryption Oracle I determined that the customization affects each of the 23 blocks of the transport stream differently next I tested the software using des weak keys these are certain keys not recommended for use with DES because their properties weaken the cryptographic strength a key of all 0 or all 1 bits will cause des decryption and encryption to be identical that is running the same data through encrypt or decrypt will give the same result I can test this on an SACP configured for standard DES decryption and see the expected weak key behavior when tested with the descrambler in custom mode the weak key behavior changes using a key of all 0 or l1 didn't produce the same results in encrypt and decrypt modes looking at the other hardware register testing the desk peripheral with different values in the 8-bit register and using weak keys shows that the standard desk weak key behavior still exists so my hunch at this point is that one customization affects the key and the other customization affects the data at this point I can't be certain but I have a good feeling about the theory so I continue to investigate based on the idea that the hardware customization affects only the key and decryption is Thai static I thought the simplest customization would be an XOR mask that's applied to the key before it's used for DES decryption XOR requires only a single gate in series with the DES engine so it fits the requirements of fast and very simple to implement in hardware a change of even a single bit in the key could cause the observed effects flipping more than 28 bits would be pointless that's the same as inverting a key in flipping fewer bits more flip bits means more gates necessary for the customization so it makes sense to flip a minimal number of bits so I wrote this wonderful four loop nested sixteen levels deep to test decryption results after flipping one bit of the key then flipping two bits and three bits and so on up to sixteen bits to test all the possible keys will take a long time but if only a few bits are flipped then it might be possible to run in a shorter period of time and promising results did come quickly it turns out the theory held up and some of the blocks have this fused three bits flipped this takes only seconds for the software to identify after verifying that these worked for XOR maps for these blocks the software then was left running to find all 23 asks the simple brute-force method worked it ran for a couple of days to identify all the 23 masks by more carefully analyzing which bits are being flipped in the early results a pattern can actually be found so the search could have been more limited using this technique the software tracker could have completed it in under a second after successfully solving the first Hardware customization the theory that the second customization is the data XOR looks promising it makes sense that one or more XOR gate is enabled by each bit of the 8-bit hardware register using the ACP as a decryption Oracle a known key in data were decrypted with all values of the 8-bit register software attack of this function was successful and 255 XOR masks for identifying behavior matching what was expected I haven't actually seen this customization in actual use presumably they're saving it to be used as a countermeasure against pirate devices when necessary but it hasn't been necessary since the system never had a security breach [Applause] in order to implement a soft cam a software implementation of the descrambler a few cryptographic details need to bite be identified but at this point I have all the tools to do so the initialization vector used for CPC mode can be found through simple acts or and the handling of short blocks those less than the 64 bit - block size can be identified likewise with all these details a software implementation of the EMM decryption of category key and ECM decryption of program key and working Keys can be made and the transport stream descrambler can also be implemented in software the rapid key changes in use of desks with hardware customizations makes it a bit different to implement compared to a soft cam for typical DVD systems but overall the concept is the same and now it's all working I was able to test it and it's fully working on both the satellite and cable systems this is a screen that's broadcast before a pay-per-view event goes live the pay-per-view like all other channels can be decrypted with a soft cam using the algorithms learned in these keys that are extracted with the ECM and EMM algorithms and seed keys for set-top box of any level of authorization the category key can be decrypted and then used to decrypt any and all of the channels that are broadcast by this provider a few of the weaknesses that I identified in this system were that the ACP I studied is relatively old technology and almost twenty years old so this makes it a lot easier for invasive analysis today than when it was brand new the tqf P 100 package is quite easy to deal with compared to modern alternatives the chip is susceptible to the voltage glitching it's a von Neumann architecture without strong MMU Protection preventing code to be executed from RAM they didn't leave any possibility for code update or dynamic code execution for countermeasure purposes the software for the ACP is contained entirely in ROM with no mechanism for software updates in the field the hardware customizations the crypto were quite simple and required no reverse engineering of the chip logic I was basically able to guess the hardware customizations I was impressed with the design of the system it was actually stronger than I anticipated when I started the project all the key handling and decryption is contained within a single chip which makes it impossible to do key sharing that's being done with some of the smart card systems the fast working key change interval only 133 milliseconds also makes key sharing more difficult and the short tight lifetime of the key makes cracking it in real time quite unrealistic the lack of code in any rewritable memory means there's nowhere to write code for a permanent backdoor to disable the access or to disable the access controls I listed this also as a weakness but in fact this is a strength as it limits the attackers capability to install any kind of persistent backdoor the chip operates on an internal clock eliminating clock glitch attack and making timing a voltage glitch a lot more difficult these dead addresses in the middle of desk keys prevent linear readout of keys if one were to cause a loop reading data to go out of bounds and reach the area of RAM where keys are stored the chip will reset before an entire key is read after the first couple of bytes a dead address will be accessed that causes the chip to reset the personalization ROM appears to be inaccessible so it can't easily be used to modify the keys and unit address within the ACP the seed keys aren't easily changed so the set-top boxes can't easily be cloned the keys exist only in RAM so you have to maintain a battery backup at all times this rules out a lot of invasive attacks to retrieve the keys there are no group keys used for EMS all unit addressing is to individual units so you have to pull keys from an actively subscribed box in order to get active keys that said if you have keys from a box that is subscribed to any channel you will receive an e mm containing the category key which is capable of decrypting all channels so you don't need to have a subscription to all channels you want to decrypt as long as you're authorized for at least one channel on the system the software is generally well designed and written I didn't notice any glaring bugs within it although des is use the EMM decryption requires using three desk keys and multiple rounds are performed when decrypting EMM and ECMs so this part isn't as simple as cracking a single 56 bit key brute forcing starting from the encrypted transport stream requires cracking working key then program key then category key and finally the 3 seed keys you might wonder how many set-top boxes it took for me to complete this project the truth is I only needed the one truckload some of the boxes had different versions of the ACP chip many of the boxes had different PCB layouts so it was interesting to be able to look at a variety of boxes the cost of you set-top boxes was low around $20.00 and for this research I was focusing on the signal security and didn't need the PVR functionality or any of the advanced features from the expensive set-top boxes so at this point I have a brief anti-piracy message I don't recommend you pirate cable or satellite TV there's never anything good on it doesn't matter how many channels you can decrypt believe me I looked it's not worth the effort do we have questions from the room questions please use the microphones I know there is one question from the interwebs okay hello yep this is working good so the first question from the internet is how many chips did you destroy or make unusable and how did you get all those setup boxes because the cost of the used set-top boxes was quite low I wasn't afraid to destroy several chips in the process it didn't take as many as I would have expected in the beginning two or three chips were used to for the decapsulation in the delayering process I ended up extracting the ROM from a single chip and then when it came to glitching there were three or four chips that I removed and erase the RAM from to develop the glitch when I finally got to the point where I was extracting heat from a valid chip the very first chip that I tried worked so there were few casualties involved thank you microphone three was the first one please how many years did this project take you I would work for a few weeks at a time and then get burnt out and take a break and then come back to it most of the work for the project was completed over about a two-year period thank you and microphone two please hi thank you for a great lecture how comes it that the content decryption was a DES and not a dvb-c essay because we used to usually that content is encrypted with dvbe csa in this division in North America we don't believe in standards Thanks the timing was also a part of it that the system was being developed at the same time as dvv was being standardized so general instrument rather than going along with a standards group and waiting for the standardization they went with desk directly thank you and another one from cyber cyber space Sabo okay another question from the internet is you had all this fancy like lab equipment and stuff how were you able to afford that I've been quite interested in this for a long time so I've collected this equipment over over a period of years and I do some work professionally in reverse engineering so whenever possible I use the clients money to buy another piece of equipment for the lab to do this actual work though you could even use more basic equipment because of the age of the chip you could use a microscope that you could find easily for 1,000 or 2,000 dollars or even less and have quite good results so it's not trivial but it's not a huge amount of money for lab equipment not that huge microphone to please and what do you do for a living besides reverse engineering reverse engineering thank you and the internet again okay next question is you the somebody wants to know how well which software did you use for the automated image analyzing and is it available somewhere Oh like everybody else that I've known that's an optical rock extraction I developed it myself everybody seems to develop their own tools from scratch for that the image processing I use was really quite simple so it didn't it didn't take a lot of advanced algorithms or anything like that so I'm using some software I develop personally and it hasn't been released microphone to please and how did you kept the books the boxes subscribed so did you call them every week oh my box broke down I got another one or how's this done for most of the research that I did I didn't need an active box I I did all the research just on previously activated boxes that had lost the authorization and by the time I had the process figured out that I knew how to extract keys from a valid box I only needed the one box and had you heard back from the cable provider about this No okay thank you microphone 3 please hello thanks very much for the lecture and well done all the work my question is how does the glitching work glitching attack for the glitcher I was was quite simple I I dropped the voltage for a very brief period of time and it's enough time that it causes at least one instruction to not execute properly but it's too short of a time to cause the chip to reset so essentially I'm corrupting one instruction as far as the specific target that I hit that led to my code in RAM I'm not actually sure I found that if I glitch at this time then the code ends up executing my code good enough for me okay thank you Chris please dear audience give an anniversary edition applause - Chris Kandinsky [Applause] [Music] you [Music]

Channel: media.ccc.de

Views: 731,049

Keywords: 33C3, CCC, Chaos, Communicaion, Congress, Hamburg, Works, for, me

Id: lhbSD1Jba0Q

Length: 62min 41sec (3761 seconds)

Published: Tue Dec 27 2016

Reddit Comments

[u/benoliver999]

Don't pirate cable or satellite TV, there's nothing on there worth watching.

The true spirit of hacking for hacking's sake.

[u/omgzrob]

Christ, when he showed off how to physically see the state of bits in ROM by wet etching the chip itself blew my mind

[u/t0mbstone]

Utterly insane. Guy is a prodigy.

[u/conairh]

If you like this and want to waste a day, check out Blackhat or DefCon on yourtube. Damn near every presentation from these cons free and for you to enjoy. Hackers love sharing. They are the best people.

Should have also plugged Chaos Computer Club's channel (this presentation is at their con). How rude of me.

[u/davebandit]

Wow, 2 years of work on the project...

[u/Plasma_000]

God damnit, this guy just doesn't give up

-Cable companies probably

[u/phafy]

My computer architecture classes came flooding back to me watching this.

[u/KurrKurr]

Didn't understand half of it, but it was very interesting nonetheless!

[u/[deleted]]

How legal is what he did? Like could the cops just roll up to his house and arrest him?

Genuinely curious.