I really don't think aids will kill off humanity or anything like that. I think that it will just decrease the population somewhat, more or less like the bubonic plage.
As for panic-inducing, I am afraid people believe whatever the heck they want to believe (safe things that are dangerous, and dangerous things that are safe). We could do with some more logical humans.:P
Nuclear power seemed like a good idea not too long ago, but in the US we are having political problems about where to dump the waste. If someone could magically deal with the waste, then I imagine nuclear power would skyrocket. Until then, it is too darn expensive ($,politically,environmentally)
I don't know about the complete implosion of the human population, but we can already see how disease is going to be wiping out a big chunk of the population. Exactly what percentage of African citizens are infected with HIV again?
If nothing else, plagues of one kind or another will cull the population a bit.
As usage of resources like fossil fuels is largely about economics, things won't change much until there is an economic reason to change. For example, nearly running out of fuels and skyrocketing prices.
Which means that we may be better off with some of those economic reasons appering in a very real way sooner rather than later, pollution-wise.
As I said above, it is more a matter of economics. This isn't like the y2k bug where there is a definite cutoff date. And the y2k bug didn't make current machines decrease in usefulness (right up until the cutoff date; not counting that the hardware would have to be changed at that time).
Land resources and several other natural resources will be conserved more/used more efficiently as it becomes economically advantageous to do so. Capitalism works that way, and the change will slowly happen with or without doomsday predictions. When wasting/using inefficent technologies becomes expensive, people will migrate on their own.
There is a EULA on the OUTSIDE of the xbox package. It forbids you from running unauthorized code. And they defend this EULA in the courts because it is plainly viewable to users before/as they are buying the unit, rather than being only visable after you open the box.
Palladin is complex enough to identify both non-trusted 'code' and 'data.' It's in their patent. Their patent is actually quite thurough.
"And what's the big deal about having "non-trusted" code loaded into RAM anyway? Actually, it's very easy to put one's own binary code into the system's memory; load it as raw data. An OOB-type exploit can pass control to that nearly as easily as it can execute a program that's been loaded but not yet determined to be trustworthy."
As I understand it, you can run unsigned code on Palladium. In the patent for their funky new OS, the features MS lists are maily for keeping unsigned codes' hands to itself. Unsigned code can't mess with signed/secure data on the hd or in ram. But it can still run; you can still have that functionality. Your current version of mame will still happily run.
Yeah, I understand what you mean. Alot of the features MS is working on would actually be pretty cool (assuming they work properly).
The problem is that the reality won't match the claims. The thing won't work properly; that is pretty much a given. However, even worse than the probable bugs is the fact that everyone will have to trust a company that consistently has proven itself to be NOT trustworthy and that freely exploits any advantages it has. That is what we are worried about.
If were were dealing with straight capitalism, we would just sit back and laugh at things like this. But things like monopolies subvert the normal functioning of capitalism, which means the mechanism to 'punish' stupidity in the marketplace are subverted. So nobody is laughing (except Gates).
I can't help but think that there are two exceptions to that rule. Doctors and lawyers are two professions that have basically been 'set up' so that they are quite profitable and legal, and enjoyable to the people interested in that kind of thing. The rich gotta set up their kids with good jobs somehow.:P
I think that the barriers in place to keep losers out of the medical field are reasonable (dont want an idiot operating on people etc) and there will always be sick people. However, lawyers... I don't think anything bad about their barriers of entry either, but they do things to keep themselves important. Like endless laws that are intentionally designed so that no normal (or even reasonally above average + educated) person can read them. Also the odd suits that we all know too well....
Well, at least this one went well. But you have to wonder why it was necessary at all.:P
I am glad that they decided this way. When a newspaper is published, do they go by the date of publication or the most recent tome someone bought a copy? Recently things have been more harshly regulated simply because they were electronic; I am glad that that isn't the case here. Maybe we can continue to get some sanity in the courts. Just a thought.:>
With the idea of MS getting control of our systems, I see the same problem here as with the old NSA_KEY silliness. You can't actually use something like the NSA_KEY without giving it away.
How do you know someone doesn't have something monitoring network traffic? So if you send your magical super-key to a computer to open it up, you have to hope that they have no such software/hardware active. If they do have such hardware/software, then the 'bad guys' now have the super key of happiness that gives them total control.
I can imagine how a terrorist would love to see their system get 'hacked' by such a universal password.
Ebay has lots of anime for sale. You can find alot of anime dvds there. Also, you could go the fansub route and get an entire series that has not been released in the US for about $15 on ebay. You can also download those same fansubs from IRC.
Yeah, covering up a crime makes you an accomplice in America. They are legally required to fess up. It seems that little things like the law aren't really considered in corporate America, as that didn't come up in the discussions in the article at all.:
I have a rating of over 100, alot of which is from buying arcade stuff. Of all my arcade transactions, only two boards have had problems, and one that had a deceptive auction title.
Yeah, some people have problems. But there is alot of good stuff to be had. To me, the many great finds outweigh the few lemons (and I am not rich!) I am just happy to get this stuff at all.
I mainly collect arcade games off ebay. Average price ~$40. Do I care about how ebay makes it less rare? Or easier to get? No, that is a GOOD thing because it means I can actually get some arcade boards for less than a few thousand dollars.:P
Strangely, emulation does significantly affect the price of boards on ebay. Macross boards (a japanese only game) used to cost about $250. Within the month of the preliminary driver for mame, the average price of that board went down to ~$95. The driver isn't even that good, and never has been updated. Yet look at the change. Hmm. Good if you want to buy the board, bad if you want to sell it.:P
My rating is over 100. I mainly use ebay to get jamma (arcade game) boards. The cheapest I got was World Heroes for $5 (shipping included!). The average price is about $40, the price of a console game.
Without ebay, I wouldn't be able to get all this stuff, no matter how much effort I put into it. But now it is easy to collect wierd stuff like that at good prices.
Community? No... I can't say I chat with the people etc. Like you, mainly I just 'what is your address/shipping?' and 'I got it safely, here is + feedback. Please return the favor.' Nothing personal/friendly really.
If they actually did start 'nuking' user's firmware for doing harddrive expansions, they will face a class action suit.
Yeah, that won't magically prevent them from doing it in the first place, but it will make them wish they didn't.
Realistically, they aren't going to use this 'feature.' It is just to say that they can stop people from pirating or whatever (which is kind of a bogus claim to begin with. Broadcasters never have been guaranteed that people must watch the commercials. People who cut the commercials aren't stealing, they are very legally viewing the signal as they see fit. Now the part about forwarding shows to friends may be legally questionable, but that too is something that can basically be done with vcrs. Vcrs are not illegal yet!)
Dude, actually read someone's post before you tell them they are wrong. Your 'correction' has nothing to do with cat_jesus' post.
ScottKin said that the hacks are mostly evil, for things like 'illegal reception.'
cat_jesus correct him in saying that most of the hacks have nothing to do with pirating; the single most common 'hack' is to replace the origional harddrive with a bigger one. Nothing evil there.
Then you 'corrected' cat_jesus by saying ReplayTV has the absolue right to terminate accounts etc... which has nothing to do with cat_jesus' post! They were talking about the nature of the hacks, not ReplayTV as a company.
m a s s a c h u s e t t s i n s t i t u t e o f t e c h n o l o g y . a r t i f i c i a l i n t e l l i g e n c e l a b o r a t o r y @ MIT 1 1 Page 2 3 Abstract This paper discusses the hardware foundations of the cryptosystem employed by the Xbox TM video game console from Microsoft. A secret boot block over-lay is buried within a system ASIC. This secret boot block decrypts and verifies portions of an external FLASH-type ROM. The presence of the secret boot block is camouflaged by a decoy boot block in the external ROM. The code contained within the secret boot block is transferred to the CPU in the clear over a set of high-speed busses where it can be extracted using simple custom hardware. The paper concludes with recommendations for improving the Xbox security system. One lesson of this study is that the use of a high-performance bus alone is not a sufficient security measure, given the advent of inexpensive, fast rapid prototyping services and high-performance FPGAs.
2 2 2 Page 3 4 1 Introduction and Background Every cryptosystem is based on some kind of secret, such as a key. Regardless of the cipher, the security of a cryptosystem is only as strong as the secrecy of the key. Thus, some of the most startlingly effective attacks on a cryptosystem involve no ciphertext analysis, but instead find flaws in the protocols that manage the keys. Cryptosystems based on symmetric ciphers are particularly vulnerable to protocol attacks, since both the sender and the receiver must be trusted to have a copy of the same secret key. Despite the difficulty of key management in symmetric ciphers, they remain attractive because of their algorithmic simplicity and high throughput when compared to public key ciphers. Symmetric cipher key management becomes especially problematic when the re-ceiving party is not trusted or is in a position that can be easily compromised. This is where tamper-resistant hardware comes into play; a summary of tamper-resistance guidelines can be found in [6]. Many systems employ tamper-resistant hardware tech-niques in varying degrees, including the Sandia National Labs' "Stronglink" microme-chanical 24-bit lock [2], the Clipper chip [1], IBM's 4758 PCI Cryptographic Copro-cessor [3], Cryptographic Smartcards [5] [4], Automatic Teller Machines (ATMs), and now, video game consoles. However, trusting inadequate physical security measures to protect important secrets is risky. [14] and [15] present examples of how some of the aforementioned tamper-resistant systems can be defeated with surprisingly simple and direct methods. In the case of the Xbox TM video game console from Microsoft, the secret being protected is a key and an algorithm for decrypting and verifying a bootloader. This bootloader then decrypts and verifies a kernel image. Both the bootloader and ker-nel image are contained in an unsecured FLASH ROM. The kernel then verifies the authenticity and integrity of the applications it runs. Thus, a chain of trust is grown, bottom up, from a seed of trust. This seed- the secret key and an algorithm- is planted in a physically secure, secret boot block. The Xbox architecture results in the deployment of large number of identical de-vices, all of which contain the same secret information. As the analysis below illus-trates, the security of such a system can be readily compromised, even if the secret is protected by tamper-resistant hardware and obscured by algorithmic complexity.
2 Xbox Hardware Cryptosystem Overview The Xbox crypto protocol presents a strong defense in the face of unsecured FLASH ROM-based modifications. Please refer to figure 1. The Xbox boots from a 512-byte secret boot block that is hard-coded into the southbridge system ASIC (the "MCPX"). This boot block performs the following functions, in order: loads the "jam tables", i. e., initializes the console chipset turns on the processor caches decrypts the kernel bootloader, contained in FLASH ROM verifies that decryption was successful jumps to the decrypted kernel bootloader
3 3 3 Page 4 5 The bootloader then performs some more system initialization, decrypts a kernel image from FLASH ROM, decompresses and verifies the decrypted image, and enters the kernel. The kernel decryption key is stored within the bootloader image. Note that the secret boot block code is structured so that the bootloader decryption key is never written to main memory, thus defeating an attack that involves eavesdropping on the main memory bus. The bootloader is encrypted with RC-4 using a 128-bit key. The decryption algo-rithm and key are stored in the secret boot block and executed by the Pentium CPU; the busses between the secret boot block and the CPU are not encrypted but assumed to be secure due to their high speeds. The decryption of the bootloader image is veri-fied by checking for a 32-bit magic number near the end of the plaintext stream. This check only ensures that the ciphertext stream was not corrupted; one with knowledge of the secret key and the magic number can easily create original bootloader images. It is fairly clear from the code structure of the secret boot block that such a simple, unreliable check was employed because there was not enough space for anything else. The magic number check might also confuse efforts to create original bootloader code based on a key obtained without full knowledge of the secret boot block's contents, such as through a personnel leak or brute force. However, a brute force approach to re-covering the bootloader is probably out of the question, since distributed. net's "bovine" effort, running for over 4 years and currently capable of testing over 100 gigakeys/ s, is still working on a 64-bit RC-5 cipher at the time of writing [7]. Given this secure boot protocol, modifying the contents of the FLASH ROM alone will stand a very low chance of revealing anything useful about the console 1.This is compounded by the fact that the FLASH ROM contains a decoy boot block with halfway reasonable looking decryption and initialization code. The algorithm in the decoy boot block is a bastardized RC-4, and of course applying this algorithm on the ROM contents yields nothing but white noise. Further discussion on how the secret boot block was discovered is contained in the next section.
3 Breaking the Physical Security This section provides a chronology of how the Xbox's physical security was reverse engineered. Reading out the FLASH ROM contents and tracing the processor's execution start-ing from the boot vector proved to be futile, as the contents of the boot block in the FLASH ROM were a decoy, cleverly designed to thwart such activity. The code within the FLASH ROM boot block followed the same general flow as the code within the secret boot block, but the decryption algorithm, the keys and the ciphertext start loca-tion were incorrect. This initially resulted in a great deal of confusion but was later explained by the discovery of the secret boot block overlay. The realization of the existence of a secret boot block happened as a result of the observation that overwriting the processor reset vector in the FLASH ROM has no effect on the Xbox boot sequence. This led to a series of experiments that mapped out
1 An important exception recently discovered is described in section 6.
4 4 4 Page 5 6 controllers key-locked hard disk (executeables, cached data, save games)
pentium CPU
NV2A northbridge + gfx
MCPX southbridge
SDRAM 64 MB
FLASH ROM (bootloader + OS kernel)
secret boot ROM
DVD drive (game data / executeables)
game controllers
dongles w/ executeables (DVD player, etc.)
IDE HyperT
SSTL-2 GTL+ 64/ 32+ 128/
21+
8/ 2
legacy 8/
24+
133 MHz
200 MHz DDR 200
MHz DDR
10 MHz
secure hardware boundary security relationship not yet known
trusted code and data: digitally signed with Microsoft private key
bus width: data/ others
bus clock rate
100Base-T USB
Figure 1: Overview of the Microsoft Xbox hardware.
5 5 5 Page 6 7 the extent of the secret boot block. The block is believed to be 512 bytes in length, situated at the highest location in processor physical memory. The following approaches were then considered for extracting the secret boot block contents: decapping the MCPX southbridge ASIC using the JTAG boundary scan on the Pentium to step through the "real" boot se-quence
probing the main memory bus for any portions of the boot block that were written to memory probing the processor-northbridge bus using a logic analyzer or custom hardware probing the HyperTransport northbridge-southbridge bus using custom hardware
The direct approach of decapping the MCPX southbridge ASIC was rejected be-cause this ASIC appears to be manufactured in a 0. 13 process with perhaps 6 or 7 metal layers (figure 2). Extracting the bootblock from this ASIC would require a de-layering facility and access to an electron microscope. While there are companies such as Chipworks that specialize in these kinds of services, it is a difficult, expensive, and time-consuming task.
Figure 2: Die shot of the MCPX Southbridge ASIC The JTAG boundary scan approach was rejected on the grounds that the TRST# pin, used to hold the JTAG chain in reset, was tied active in a manner that was difficult to modify without removing the processor. Removal and socketing of the processor was considered to be prohibitively expensive and time consuming; the cost of a BGA socket for the Pentium III is estimated to be in the hundreds to thousands of dollars. In addition, the JTAG boundary scan codes for the Pentium III are largely proprietary and would have to be reverse engineered as well. SDRAM probing was rejected on the grounds that far too many pins (128 data pins
6 6 6 Page 7 8 alone) had to be simultaneously probed, and on the grounds that the decryption routine and/ or key could be held entirely in processor cache and never written to SDRAM. Also, the cost of solder-on TQFP-100-to-logic-analyzer adapters is prohibitive (around $600 per adapter; four are required). Probing the processor-northbridge bus was re-jected for similar reasons: at least 64 data pins had to be probed, and tapping such a large number of GTL+ signals without causing signal integrity issues was thought to be very difficult. The northbridge-southbridge bus, however, showed promise because of its sim-plicity. The bus has a low signal count (10 unique) and all the signal traces are laid out on the console's motherboard in a straight flow-through fashion (12-mil center-to-center spacing within a differential pair, 13-mil spacing between differential pairs, see figure 4). In addition, the clock and strobe signals for both the transmit and receive directions are clearly labeled on the motherboard, perhaps for manufacturing debug and test reasons (figure 3). Data on the nVidia nForce chipset [9], a close relative to the Xbox chipset, indicates that the bus uses the HyperTransport (formerly known as Lightning Data Transport (LDT)) protocol. The specifications for the HyperTransport protocol are open and readily available. [8]
Figure 3: HyperTransport bus layout showing silkscreen information The primary difficulties in tapping the HyperTransport bus are its high speed (200 MHz DDR) and its use of differential signaling (few logic analyzers come with support for differential signaling). It is interesting to note that HyperTransport bus protocol
7 7 7 Page 8 9 analyzers are commercially available from vendors such as FuturePlus, but they cost upward of $25,000. This price does not include the high-end logic analyzer required to drive the protocol analyzer. The alternative solution to tapping the northbridge-southbridgeHyperTransport bus was to build a relatively cheap, fully custom, differential-to-single-ended "Tap Board", and to connect the output of this board to an FPGA. A Xilinx Virtex-E part was used in this study because it was readily available, as it was used as part of the author's thesis work; however, a better choice would be any of the new Xilinx Virtex-II FPGAs. A suitable Virtex-II FPGA would cost about $50 in single quantities. The custom Tap Board uses a two-layer, 6 mil trace/ space, 15 mil hole process from Advanced Circuits, offered at a price of $33 per board in small quantities. A Texas Instruments SN65LVDS386 LVDS-to-TTL converter was used to turn the differential HyperTransport signals into a single-ended format. It turns out that the HyperTransport physical signaling specification is similar to LVDS, but with a different common-mode offset. The output of the converter drives a cable to the FPGA board. The FPGA is configured to receive the high speed signals with the CTT (Center-Tap Terminated) "Select I/ O" option. CTT is chosen because it allows the single-ended TTL drivers to be terminated with a low impedance to 1. 5V and still function properly. Note that although Virtex-E FPGAs support LVDS directly, the target FPGA board was not originally designed to support the LVDS configuration.
12 mil 13 mil 12 mil
differential signal pair
6 mil trace
Figure 4: Dimensions of the HyperTransport signal traces on the motherboard. The Tap Board has on one edge a pattern of traces with no soldermask that matches the pattern of traces on the Xbox motherboard. The Tap Board was soldered directly to the Xbox's northbridge-southbridge bus. Only the receive-direction Tap Board was mounted for this study. The mating edge was shaped using a belt sander, so that the tapping traces were flush with the edge of the board, and the board could be mounted at a reclined angle to enhance solderability. The soldermask on the Xbox was removed with fine-grit sand paper, and the Tap Board was carefully aligned by hand, and then held roughly in place by soldering a coarse piece of wire between the Tap Board and the motherboard. A hard-setting adhesive, such as Miller-Stephenson Epoxy 907, was ap-plied to fix the angle and mating distance of the Tap board to the motherboard; once the epoxy was cured, the holding wire was removed, and the traces between the Tap Board
8 8 8 Page 9 10 and the Xbox motherboard were easily soldered using a fine-tip iron and a microscope. Figure 5: Tap Board connected to the FPGA board. The FPGA board was originally developed by the author for another work.
The polarity of the HyperTransport bus signals was determined by probing the idle state of the wires, assuming that their idle state had a value of 0x00. Those signals that had the positive and negative pairs swapped relative to the Tap board layout idled to a "1". Signals with inverted polarity were restored to their true value within the trace capture FPGA.
Figure 6: Close-up of the Tap Board mounted in the Xbox A Xilinx Virtex-E FPGA was used to capture traces of HyperTransport bus activ-ity. It was difficult getting the FPGA to manage the 200 MHz DDR data rates with
9 9 9 Page 10 11 low skew. However, careful hand-layout of the input registers, post-layout timing sim-ulations at nominal temperature and voltage, and iterations to manually tweak delays and skews eventually centered the clock signal within the data signal on the FPGA's input registers. The retimed data was then demultiplexed to a very manageable 100 MHz single-data rate 32-bit wide bus and written into a bank of FIFOs, along with a sequence count that recorded at what cycle relative to a reset signal the data was captured. Some additional logic was incorporated into the FPGA that discarded idle values (0x0000 0000) from the trace FIFOs and formatted the deserialized data relative to the strobe signal, clearly identified on the Xbox motherboard as "RXD8 / RXD* 8" (figure 3) in sector 5D (the Xbox motherboard has a coordinate system printed on its periphery). The reset signal can be determined by probing traces near the HyperTransport bus that behaved like a reset signal. In reality, it is possible that some signal that was not the true reset signal was used to trigger the trace capture, but that is irrelevant as the signal chosen seemed to display a consistent timing relationship with respect to the bus. In fact, the signal used to trigger the trace capture exhibited a 350 ns runt pulse about 67 ms after power-on-reset; this runt pulse was filtered out by a state machine, as it was erroneously restarting the trace capture. Once traces of data were captured by the FPGA, the order of the bits on the Hy-perTransport bus relative to the Tap Board layout could be determined. This can be done by correlating known values in the FLASH ROM with data values captured on the HyperTransport bus. A 1's count can be used to identify candidate patterns and data sequences for manual correlation. Fortunately, very early on in the trace several distinctive, sequential values are grabbed from the FLASH ROM: a few values from the lowest address in FLASH ROM, followed by a few values from the boot vector, which happens to be identical between the decoy FLASH ROM contents and the secret boot ROM contents. The order of the traces for the receive-direction bus on the moth-erboard are believed to be, from the outside to the inside, bit 8 (CTL strobe), 4#, 0#, 7#, 2#, 3#, CLK#, 5, 6#, and 1#. Signals with # after them are inverted with respect to the Tap Board layout. The raw trace data captured by the FPGA was then dumped to files and manually processed. An example illustrating the format of trace data can be found in figure 7. The sequence number was critical in determining the boundaries of cache traces; blocks of 8 or 16 words are fetched by the processor, even when the caches are off. Trace data was differentiated between secret boot code and FLASH ROM data by searching for the first word of the candidate trace in a dump of the FLASH ROM; if the data could not be found in the FLASH ROM, it was guessed to be secret boot code. Because the processor boots with its caches off, the first roughly 24 million bus cycles contained repeated line fills of the "jam table" initialization code, and were ignored as they just performed the wrote initialization of the chipsets. The caches were then turned on by the boot code, and very clear and simple to read blocks of instructions and data were found. These instruction traces were mapped into the secret boot block using the decoy FLASH ROM boot block as a template. The recovered block of code was then disassembled, and the decryption algorithm was determined to be 128-bit RC-4. Because the location of the 128-bit key within the secret boot block was ambiguous (the Tap Board only provides data traces without addresses), a brute-force search was
Figure 7: An example illustrating the format of trace data captured by the FPGA. Format of the data is "sequence : data::: aligner : unaligned data".
utilized to help isolate the key. A 16-byte sliding "guess key" window over the captured data trace was used as input to an RC-4 decryption engine, and a histogram of the data output was used to determine when the key was found. This information helped resolve some ambiguities in the placement of the data within the secret boot block, and a full picture of the important code within the secret boot block was assembled. Now that the secret boot procedure is understood, it is possible to encrypt a new ROM for the Xbox console, and to further study the structure of the Xbox bootloader and kernel. Given the RC-4 algorithm, the 128-bit key, and the magic check number at the end of the decrypted segment, one can run original code on the Xbox.
4 Lessons Learned One lesson of this study is that the use of a high-performance bus alone is not a suf-ficient security measure; the advent of cheap, fast rapid prototyping services and high performance FPGAs allows even poor students to create devices that can tap the bus. However, encrypting a bus introduces its own problems. A secure cipher on a high per-formance bus significantly impacts latency, power consumption, and reliability. Power consumption is increased because the activity factor for the bus approaches 100%, if the encryption scheme is any good. In this case, the power consumed driving the bus
11 11 11 Page 12 13 would increase by over an order of magnitude, as the observed activity factor on the northbridge-southbridge bus was well below 10%. Reliability is hurt because a single bit error, even during an idle cycle, can corrupt large blocks of data; with a stream cipher, the corruption would extend until the stream is resynchronized. A compromise solution to the problem is to simply not trust any bus in the system. In this case, the secret boot block might employ a digital signature protocol, such as Authenticode R , using public key algorithms and one-way hashes. [10] Then, all secu-rity rests in the secrecy of the private key, and the strength of the public key algorithm. In order to prevent employee leaks from spreading a private key, a system similar to the BBN SignAssure TM could be used to manage the key so that no human ever has knowl-edge of the private key. The principal drawback of this method is that it requires extra silicon area to be spent on storing a larger secret boot block, as it is probably difficult, if not impossible, to code a full public key encryption algorithm plus key storage and hardware initialization code within 512 bytes. The above suggestion does not prevent someone from eavesdropping and obtaining the plaintext of the operating system code, but it does effectively defeat any attempt to run original code. The public key scheme could be defeated, however, by a mech-anism that snoops the main memory bus and patches plaintext in main memory. As discussed previously, this approach is possible, but difficult; however, the tenacity of an attacker should not be underestimated. For example, a known attack on the Sony Playstation2 console was developed that is rumored to work by dynamically patching its high-performance RAMBUS memory system. The difficulty of a memory patch at-tack could be increased by using a simple periodic hash and check of the critical code regions in memory. Buffer overrun exploits are also a point of weakness, and they work regardless of the secret boot protocol. An attacker sniffing an insecure bus could obtain the de-crypted kernel code and analyze it for weaknesses. However, any machine architecture that employs guarded pointers [11] is much more difficult, if not impossible, to attack using buffer overruns. A fast, efficient guarded pointer scheme with a simple hardware implementation is described in [12]. This scheme can easily be adapted to work in a 64-bit architecture. A. Kerckhoffs (1835-1903) once stated that the security of a cryptosystemmust not depend on keeping the algorithmsecret; this is referred to as Kerckhoffs' Principle.[ 13] Another way of stating this is that there is no security through obscurity. In particular, it is an error to assume that a secret, distributed along with the information it guards, is never revealed. For example, the Sega Dreamcast uses a proprietary GD-ROMsoftware format; but, the drive can read CD-ROM disks. The discovery of a back door in the Dreamcast OS allowed executables to be run directly from a standard CD-ROM, thus nullifying the barrier presented by the proprietary GD-ROMformat. Other systems that rely on well-hidden secrets, including the Clipper chip [14] and the smartcards used widely throughout Europe to control access to services such as pay-TV, cell phones and gas, have been shown to be surprisingly vulnerable. [15] In this case, the Tap Board and trace capture FPGA design was developed in spare time over the duration of three weeks- including the 5-day turn time for board fabrication- for a total cost of around $50 per board. In other words, if you ship your secrets in your hardware, it is a good assumption that the users will eventually- and perhaps quickly- know your secrets.
12 12 12 Page 13 14 The failure of the Microsoft Xbox console security protocol is compounded by the fact that, as a console manufacturer, design-for-test and design-for-manufacturability is paramount. Creating a console with too much security makes it difficult to debug and manufacture. For example, the backside of the Xbox motherboard is populated with test points- including test points for every pin on the FLASH ROM. These were originally installed because of the desire to quickly test for faults during manufactur-ing. The flip side is that one could build a custom "bed-of-nails" tester jig that uses the the FLASH-ROM test points to reprogram Xbox motherboards with any desired code. This method would be fast, inexpensive and solder-free. The lesson here is that even if a manufacturer is very confident about their trust model and security protocols, it must guard against the possibility that they may someday be broken. To this extent, a sim-ple physical security measure, such as a spray-on conformal coating, would severely hamper the re-use of test structures for improper purposes. This of course greatly com-plicates the repair of hardware failures in the field, but that is a business trade-off the manufacturer must make. A more radical alternative would be to design the gaming system using proprietary hardware and proprietary media formats, thus limiting the practical impact of any at-tack on the console. Game consoles are manufactured in very high volumes, so the cost of developing a simple but effective proprietary format can be amortized. The format could then be patented, providing protection against unauthorized use without the need for secrecy. This approach was taken by Nintendo with their Nintendo 64 console. [16] Although patents have a 20 year lifetime, this is an eternity in the video game console industry: the original Nintendo Entertainment System (NES) had its debut in 1985.
5 Future Work Understanding the secret Xbox boot protocol is just the first step in understanding the Xbox. It is now possible to investigate the kernel and bootloader in more detail. It has been determined that the kernel is also encrypted with RC-4/ 128, and it is also believed to be compressed using LZX compression, a scheme employed by Microsoft's canonical distribution format, the "Cabinet" file. The structure and function of the kernel is still being investigated. One important issue to investigate is the privacy of users who use the Xbox for on-line tasks. It is known, through a parallel effort of the author, that information such as the serial number of the console is stored electronically and is probably accessible to the kernel. What happens to this information when the Xbox is plugged into the internet? Because of the encryption used to secure the Xbox, the nature of the information that is relayed to Microsoft's on-line game servers is unknown. Thus, important future work is to try to determine what the Xbox reveals about the user's identity and personal gaming habits.
13 13 13 Page 14 15 6 Addendum It has recently been called to the author's attention that the hardware initialization pro-cedure of the Xbox contains a significant weakness. [17] Recall from section 2 that the first step in the Xbox boot process is to load the "jam tables" that configure the console's chipsets. This jam table initialization procedure involves a lengthy and com-plex sequence of writes to various memory-mapped hardware register locations. As a result, the initialization procedure is implemented using a simple bytecode interpreter that reads initialization commands and data from the FLASH ROM. These bytecode commands- stored as plaintext- can be manipulated to cause the initialization procedure to abort before the kernel decryption/ verification routine is executed, and to instead run insecure code directly out of the FLASH ROM. In other words, with plaintext-only modifications in the FLASH ROM, one can entirely bypass the Xbox's security mech-anism. One could easily fix this security hole, however, by verifying the jam table's contents prior to bytecode execution with a one-way hash function, or by explicitly coding all initialization functions within the secure boot block. Both of these solutions, however, would require the secure boot block to grow significantly from its current 512-byte size, and neither solution allows easy changes to the initialization procedure in case a bug is found or in case the hardware evolves as a result of cost reduction efforts.
Acknowledgments The author would like to acknowledge the support of the on-line electronic community. The author would also like to thank the Electronic Frontier Foundation for providing legal counsel. Hal Abelson and Tom Knight also provided invaluable moral support. Finally, the author would like to thank Nikki Justis for all her love and support, and for giving him such an interesting toy for Christmas.
References [1] Federal Information Processing Standards Publication, FIPS PUB 185: Escrowed Encryption Standard (EES) http:// www. itl. nist. gov/ fipspubs/ fip185. htm
[2] Thomas W. Krygowski, Jeffry J. Sniegowski, M. Steven Rodgers, Stephen Montague, James J. Allen, Jerome F. Jakubczak, Samuel L. Miller, Infras-tructure, Technology and Applications Of Micro-Electro-Mechanical Systems (MEMS), Sandia National Laboratories, Intelligent Micromachine Department, http:// www. mdl. sandia. gov/ Micromachine, also appears in Sensor Expo 1999.
[4] Gemplus (a smartcard vendor), Gemplus Corporate Website, http:// www. gemplus. com
14 14 14 Page 15 [5] Pil Joon Lee, Eun Jeong Lee, Yong Duk Kim, How to Implement Cost-Effective and Secure Public Key Cryptosystems Proceedings of the First International Work-shop on Cryptographic Hardware and Embedded Systems (CHES), August 1999.
[6] Federal Information Processing Standards Publication, FIPS PUB 140-2: Security Requirements for Cryptographic Modules, http:// csrc. nist. gov/ publications/ fips/ fips140-2/ fips1402.pdf
[7] distributed. net, distributed. net: Project RC5, http:// www. distributed. net/ rc5/ [8] HyperTransport Consortium, HyperTransport TM I/ O Link Specification, Version 1.03, http:// www. hypertransport. org
[10] Microsoft Developer Network, Introduction to Code Signing, http:// msdn. microsoft. com/ workshop/ security/ authcode/ intro authenticode. asp
[11] Nicholas P. Carter, Stephen W. Keckler, and William J. Dally, Hardware support for fast capability-based addressing, Proceedings of ASPLOS VI, October 1994, pp. 319-27.
[12] Jeremy Brown, J. P. Grossman, Andrew Huang, and Thomas F. Knight, Jr., A capability representation with embedded address and nearly-exact object bounds, Project Aries Technical Memo 5, http:// www. ai. mit. edu/ projects/ aries/ Documents/ Memos/ ARIES-05. pdf
[13] Auguste Kerckhoffs, La cryptographie militaire, Journal des sciences militaires, vol. IX, pp. 5-38, Jan. 1883, pp. 161-191, Feb. 1883.
[14] R. Anderson and M. Kuhn, Tamper Resistance -a Cautionary Note, Proceedings of the Second Usenix Workshop on Electronic Commerce, pp. 1- 11, November 1996.
[15] R. Anderson and M. Kuhn, Low Cost Attacks on Tamper Resistant Devices, IWSP: International Workshop on Security Protocols, LNCS, 1997.
[16] Van Hook, et al., High Performance Low Cost Video Game System with Co-processor Providing High Speed Efficient 3D Graphics and Digital Audio Signal Processing, U. S. Patent 6, 239,810, May 29, 2001.
[17] Private conversation with visor. visor can be reached by sending a personal mes-sage to visor on www. xboxhacker. net
The space shuttle is well armored. Yet when the thing was origionally designed, nobody knew how common high velocity (but tiny) rocks would be up there. It turned out that the shuttle had insufficient armor to deal with micrometeorites for very long. That is why you see clips of the shuttle 'flying backwards' while in orbit. There is more armor on that side...
"(a) Photons are massless, so you can't use newtonian gravity F=GmM/r^2 to compute gravitation effects on it. I trust that you are not saying that light is not affected by gravity? The mass of photons is debatable, but it is a well known, observed fact that light is indeed affected by gravity."
It is indeed observed. In fact, this was one of the first things that 'proved' the Theory of Relativity. An expedition to Africa was made to observe the sun during an eclipse. If photons were affected by gravity, then the light passing near the sun (which is normally drowned out by the sun's light, but isn't drowned out during an eclipse) would be distorted. Well, the distortion was observed.:>
Slashdot Mirror
Thanks for the number.
:P
I really don't think aids will kill off humanity or anything like that. I think that it will just decrease the population somewhat, more or less like the bubonic plage.
As for panic-inducing, I am afraid people believe whatever the heck they want to believe (safe things that are dangerous, and dangerous things that are safe). We could do with some more logical humans.
Nuclear power seemed like a good idea not too long ago, but in the US we are having political problems about where to dump the waste. If someone could magically deal with the waste, then I imagine nuclear power would skyrocket. Until then, it is too darn expensive ($,politically,environmentally)
I don't know about the complete implosion of the human population, but we can already see how disease is going to be wiping out a big chunk of the population. Exactly what percentage of African citizens are infected with HIV again?
If nothing else, plagues of one kind or another will cull the population a bit.
As usage of resources like fossil fuels is largely about economics, things won't change much until there is an economic reason to change. For example, nearly running out of fuels and skyrocketing prices.
Which means that we may be better off with some of those economic reasons appering in a very real way sooner rather than later, pollution-wise.
As I said above, it is more a matter of economics. This isn't like the y2k bug where there is a definite cutoff date. And the y2k bug didn't make current machines decrease in usefulness (right up until the cutoff date; not counting that the hardware would have to be changed at that time).
Land resources and several other natural resources will be conserved more/used more efficiently as it becomes economically advantageous to do so. Capitalism works that way, and the change will slowly happen with or without doomsday predictions. When wasting/using inefficent technologies becomes expensive, people will migrate on their own.
There is a EULA on the OUTSIDE of the xbox package. It forbids you from running unauthorized code. And they defend this EULA in the courts because it is plainly viewable to users before/as they are buying the unit, rather than being only visable after you open the box.
Bummer.
Palladin is complex enough to identify both non-trusted 'code' and 'data.' It's in their patent. Their patent is actually quite thurough.
"And what's the big deal about having "non-trusted" code loaded into RAM anyway? Actually, it's very easy to put one's own binary code into the system's memory; load it as raw data. An OOB-type exploit can pass control to that nearly as easily as it can execute a program that's been loaded but not yet determined to be trustworthy."
Right now people just use the ethernet connection to move files between their ps2 and pc.
You can in theory use a sub cd drive to read cd-r, rw and music cds, but I don't know of anyone who got that to work yet.
As I understand it, you can run unsigned code on Palladium. In the patent for their funky new OS, the features MS lists are maily for keeping unsigned codes' hands to itself. Unsigned code can't mess with signed/secure data on the hd or in ram. But it can still run; you can still have that functionality. Your current version of mame will still happily run.
Yeah, I understand what you mean. Alot of the features MS is working on would actually be pretty cool (assuming they work properly).
The problem is that the reality won't match the claims. The thing won't work properly; that is pretty much a given. However, even worse than the probable bugs is the fact that everyone will have to trust a company that consistently has proven itself to be NOT trustworthy and that freely exploits any advantages it has. That is what we are worried about.
If were were dealing with straight capitalism, we would just sit back and laugh at things like this. But things like monopolies subvert the normal functioning of capitalism, which means the mechanism to 'punish' stupidity in the marketplace are subverted. So nobody is laughing (except Gates).
I can't help but think that there are two exceptions to that rule. Doctors and lawyers are two professions that have basically been 'set up' so that they are quite profitable and legal, and enjoyable to the people interested in that kind of thing. The rich gotta set up their kids with good jobs somehow. :P
:P
I think that the barriers in place to keep losers out of the medical field are reasonable (dont want an idiot operating on people etc) and there will always be sick people. However, lawyers... I don't think anything bad about their barriers of entry either, but they do things to keep themselves important. Like endless laws that are intentionally designed so that no normal (or even reasonally above average + educated) person can read them. Also the odd suits that we all know too well....
Well, at least this one went well. But you have to wonder why it was necessary at all.
I am glad that they decided this way. When a newspaper is published, do they go by the date of publication or the most recent tome someone bought a copy? Recently things have been more harshly regulated simply because they were electronic; I am glad that that isn't the case here. Maybe we can continue to get some sanity in the courts. Just a thought. :>
With the idea of MS getting control of our systems, I see the same problem here as with the old NSA_KEY silliness. You can't actually use something like the NSA_KEY without giving it away.
How do you know someone doesn't have something monitoring network traffic? So if you send your magical super-key to a computer to open it up, you have to hope that they have no such software/hardware active. If they do have such hardware/software, then the 'bad guys' now have the super key of happiness that gives them total control.
I can imagine how a terrorist would love to see their system get 'hacked' by such a universal password.
Or am I totally missing something?
Dude, it was on the front page of the cnn website. What more do you want? Billboards?
I agree that the media has problems, but keep your arguments sane.
Ebay has lots of anime for sale. You can find alot of anime dvds there. Also, you could go the fansub route and get an entire series that has not been released in the US for about $15 on ebay. You can also download those same fansubs from IRC.
Feel the power of the net!
Yeah, covering up a crime makes you an accomplice in America. They are legally required to fess up. It seems that little things like the law aren't really considered in corporate America, as that didn't come up in the discussions in the article at all. :
I have a rating of over 100, alot of which is from buying arcade stuff. Of all my arcade transactions, only two boards have had problems, and one that had a deceptive auction title.
Yeah, some people have problems. But there is alot of good stuff to be had. To me, the many great finds outweigh the few lemons (and I am not rich!) I am just happy to get this stuff at all.
I mainly collect arcade games off ebay. Average price ~$40. Do I care about how ebay makes it less rare? Or easier to get? No, that is a GOOD thing because it means I can actually get some arcade boards for less than a few thousand dollars. :P
:P
Strangely, emulation does significantly affect the price of boards on ebay. Macross boards (a japanese only game) used to cost about $250. Within the month of the preliminary driver for mame, the average price of that board went down to ~$95. The driver isn't even that good, and never has been updated. Yet look at the change. Hmm. Good if you want to buy the board, bad if you want to sell it.
My rating is over 100. I mainly use ebay to get jamma (arcade game) boards. The cheapest I got was World Heroes for $5 (shipping included!). The average price is about $40, the price of a console game.
Without ebay, I wouldn't be able to get all this stuff, no matter how much effort I put into it. But now it is easy to collect wierd stuff like that at good prices.
Community? No... I can't say I chat with the people etc. Like you, mainly I just 'what is your address/shipping?' and 'I got it safely, here is + feedback. Please return the favor.' Nothing personal/friendly really.
Still, it is kool in general.
If they actually did start 'nuking' user's firmware for doing harddrive expansions, they will face a class action suit.
Yeah, that won't magically prevent them from doing it in the first place, but it will make them wish they didn't.
Realistically, they aren't going to use this 'feature.' It is just to say that they can stop people from pirating or whatever (which is kind of a bogus claim to begin with. Broadcasters never have been guaranteed that people must watch the commercials. People who cut the commercials aren't stealing, they are very legally viewing the signal as they see fit. Now the part about forwarding shows to friends may be legally questionable, but that too is something that can basically be done with vcrs. Vcrs are not illegal yet!)
Dude, actually read someone's post before you tell them they are wrong. Your 'correction' has nothing to do with cat_jesus' post.
ScottKin said that the hacks are mostly evil, for things like 'illegal reception.'
cat_jesus correct him in saying that most of the hacks have nothing to do with pirating; the single most common 'hack' is to replace the origional harddrive with a bigger one. Nothing evil there.
Then you 'corrected' cat_jesus by saying ReplayTV has the absolue right to terminate accounts etc... which has nothing to do with cat_jesus' post! They were talking about the nature of the hacks, not ReplayTV as a company.
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::: aligner : unaligned data".
Pages 1--15 from E:\paperailab\paper.dvi
Page 1 2
Keeping Secrets in Hardware:
the Microsoft XBox TM Case
Study
Andrew . bunnie . Huang
AI Memo 2002-008 May 26, 2002
© 2 0 0 2 m a s s a c h u s e t t s i n s t i t u t e o f t e c h n o l o g y , c a m b r i d g e , m a 0 2 1 3 9 u s a . w w w. a i . m i t . e d u
m a s s a c h u s e t t s i n s t i t u t e o f t e c h n o l o g y . a r t i f i c i a l i n t e l l i g e n c e l a b o r a t o r y
@ MIT 1
1 Page 2 3
Abstract
This paper discusses the hardware foundations of the cryptosystem employed
by the Xbox TM video game console from Microsoft. A secret boot block over-lay
is buried within a system ASIC. This secret boot block decrypts and verifies
portions of an external FLASH-type ROM. The presence of the secret boot block
is camouflaged by a decoy boot block in the external ROM. The code contained
within the secret boot block is transferred to the CPU in the clear over a set of
high-speed busses where it can be extracted using simple custom hardware. The
paper concludes with recommendations for improving the Xbox security system.
One lesson of this study is that the use of a high-performance bus alone is not a
sufficient security measure, given the advent of inexpensive, fast rapid prototyping
services and high-performance FPGAs.
2 2
2 Page 3 4
1 Introduction and Background
Every cryptosystem is based on some kind of secret, such as a key. Regardless of the
cipher, the security of a cryptosystem is only as strong as the secrecy of the key. Thus,
some of the most startlingly effective attacks on a cryptosystem involve no ciphertext
analysis, but instead find flaws in the protocols that manage the keys. Cryptosystems
based on symmetric ciphers are particularly vulnerable to protocol attacks, since both
the sender and the receiver must be trusted to have a copy of the same secret key.
Despite the difficulty of key management in symmetric ciphers, they remain attractive
because of their algorithmic simplicity and high throughput when compared to public
key ciphers.
Symmetric cipher key management becomes especially problematic when the re-ceiving
party is not trusted or is in a position that can be easily compromised. This
is where tamper-resistant hardware comes into play; a summary of tamper-resistance
guidelines can be found in [6]. Many systems employ tamper-resistant hardware tech-niques
in varying degrees, including the Sandia National Labs' "Stronglink" microme-chanical
24-bit lock [2], the Clipper chip [1], IBM's 4758 PCI Cryptographic Copro-cessor
[3], Cryptographic Smartcards [5] [4], Automatic Teller Machines (ATMs), and
now, video game consoles. However, trusting inadequate physical security measures to
protect important secrets is risky. [14] and [15] present examples of how some of the
aforementioned tamper-resistant systems can be defeated with surprisingly simple and
direct methods.
In the case of the Xbox TM video game console from Microsoft, the secret being
protected is a key and an algorithm for decrypting and verifying a bootloader. This
bootloader then decrypts and verifies a kernel image. Both the bootloader and ker-nel
image are contained in an unsecured FLASH ROM. The kernel then verifies the
authenticity and integrity of the applications it runs. Thus, a chain of trust is grown,
bottom up, from a seed of trust. This seed- the secret key and an algorithm- is planted
in a physically secure, secret boot block.
The Xbox architecture results in the deployment of large number of identical de-vices,
all of which contain the same secret information. As the analysis below illus-trates,
the security of such a system can be readily compromised, even if the secret is
protected by tamper-resistant hardware and obscured by algorithmic complexity.
2 Xbox Hardware Cryptosystem Overview
The Xbox crypto protocol presents a strong defense in the face of unsecured FLASH
ROM-based modifications. Please refer to figure 1. The Xbox boots from a 512-byte
secret boot block that is hard-coded into the southbridge system ASIC (the "MCPX").
This boot block performs the following functions, in order:
loads the "jam tables", i. e., initializes the console chipset
turns on the processor caches
decrypts the kernel bootloader, contained in FLASH ROM
verifies that decryption was successful
jumps to the decrypted kernel bootloader
3 3
3 Page 4 5
The bootloader then performs some more system initialization, decrypts a kernel
image from FLASH ROM, decompresses and verifies the decrypted image, and enters
the kernel. The kernel decryption key is stored within the bootloader image. Note that
the secret boot block code is structured so that the bootloader decryption key is never
written to main memory, thus defeating an attack that involves eavesdropping on the
main memory bus.
The bootloader is encrypted with RC-4 using a 128-bit key. The decryption algo-rithm
and key are stored in the secret boot block and executed by the Pentium CPU;
the busses between the secret boot block and the CPU are not encrypted but assumed
to be secure due to their high speeds. The decryption of the bootloader image is veri-fied
by checking for a 32-bit magic number near the end of the plaintext stream. This
check only ensures that the ciphertext stream was not corrupted; one with knowledge
of the secret key and the magic number can easily create original bootloader images.
It is fairly clear from the code structure of the secret boot block that such a simple,
unreliable check was employed because there was not enough space for anything else.
The magic number check might also confuse efforts to create original bootloader code
based on a key obtained without full knowledge of the secret boot block's contents,
such as through a personnel leak or brute force. However, a brute force approach to re-covering
the bootloader is probably out of the question, since distributed. net's "bovine"
effort, running for over 4 years and currently capable of testing over 100 gigakeys/ s, is
still working on a 64-bit RC-5 cipher at the time of writing [7].
Given this secure boot protocol, modifying the contents of the FLASH ROM alone
will stand a very low chance of revealing anything useful about the console 1
is compounded by the fact that the FLASH ROM contains a decoy boot block with
halfway reasonable looking decryption and initialization code. The algorithm in the
decoy boot block is a bastardized RC-4, and of course applying this algorithm on the
ROM contents yields nothing but white noise. Further discussion on how the secret
boot block was discovered is contained in the next section.
3 Breaking the Physical Security
This section provides a chronology of how the Xbox's physical security was reverse
engineered.
Reading out the FLASH ROM contents and tracing the processor's execution start-ing
from the boot vector proved to be futile, as the contents of the boot block in the
FLASH ROM were a decoy, cleverly designed to thwart such activity. The code within
the FLASH ROM boot block followed the same general flow as the code within the
secret boot block, but the decryption algorithm, the keys and the ciphertext start loca-tion
were incorrect. This initially resulted in a great deal of confusion but was later
explained by the discovery of the secret boot block overlay.
The realization of the existence of a secret boot block happened as a result of the
observation that overwriting the processor reset vector in the FLASH ROM has no
effect on the Xbox boot sequence. This led to a series of experiments that mapped out
1 An important exception recently discovered is described in section 6.
4 4
4 Page 5 6
controllers
key-locked
hard disk
(executeables,
cached data,
save games)
pentium
CPU
NV2A
northbridge
+ gfx
MCPX
southbridge
SDRAM
64 MB
FLASH
ROM
(bootloader
+ OS kernel)
secret boot
ROM
DVD drive
(game data /
executeables)
game
controllers
dongles w/
executeables
(DVD player,
etc.)
IDE
HyperT
SSTL-2
GTL+
64/
32+ 128/
21+
8/
2
legacy
8/
24+
133
MHz
200
MHz
DDR 200
MHz
DDR
10
MHz
secure hardware boundary
security relationship
not yet known
trusted code
and data:
digitally signed
with Microsoft
private key
bus width:
data/ others
bus clock
rate
100Base-T
USB
Figure 1: Overview of the Microsoft Xbox hardware.
5 5
5 Page 6 7
the extent of the secret boot block. The block is believed to be 512 bytes in length,
situated at the highest location in processor physical memory.
The following approaches were then considered for extracting the secret boot block
contents:
decapping the MCPX southbridge ASIC
using the JTAG boundary scan on the Pentium to step through the "real" boot se-quence
probing the main memory bus for any portions of the boot block that were written
to memory
probing the processor-northbridge bus using a logic analyzer or custom hardware
probing the HyperTransport northbridge-southbridge bus using custom hardware
The direct approach of decapping the MCPX southbridge ASIC was rejected be-cause
this ASIC appears to be manufactured in a 0. 13 process with perhaps 6 or 7
metal layers (figure 2). Extracting the bootblock from this ASIC would require a de-layering
facility and access to an electron microscope. While there are companies such
as Chipworks that specialize in these kinds of services, it is a difficult, expensive, and
time-consuming task.
Figure 2: Die shot of the MCPX Southbridge ASIC
The JTAG boundary scan approach was rejected on the grounds that the TRST#
pin, used to hold the JTAG chain in reset, was tied active in a manner that was difficult
to modify without removing the processor. Removal and socketing of the processor
was considered to be prohibitively expensive and time consuming; the cost of a BGA
socket for the Pentium III is estimated to be in the hundreds to thousands of dollars. In
addition, the JTAG boundary scan codes for the Pentium III are largely proprietary and
would have to be reverse engineered as well.
SDRAM probing was rejected on the grounds that far too many pins (128 data pins
6 6
6 Page 7 8
alone) had to be simultaneously probed, and on the grounds that the decryption routine
and/ or key could be held entirely in processor cache and never written to SDRAM.
Also, the cost of solder-on TQFP-100-to-logic-analyzer adapters is prohibitive (around
$600 per adapter; four are required). Probing the processor-northbridge bus was re-jected
for similar reasons: at least 64 data pins had to be probed, and tapping such a
large number of GTL+ signals without causing signal integrity issues was thought to
be very difficult.
The northbridge-southbridge bus, however, showed promise because of its sim-plicity.
The bus has a low signal count (10 unique) and all the signal traces are laid
out on the console's motherboard in a straight flow-through fashion (12-mil center-to-center
spacing within a differential pair, 13-mil spacing between differential pairs, see
figure 4). In addition, the clock and strobe signals for both the transmit and receive
directions are clearly labeled on the motherboard, perhaps for manufacturing debug
and test reasons (figure 3). Data on the nVidia nForce chipset [9], a close relative to
the Xbox chipset, indicates that the bus uses the HyperTransport (formerly known as
Lightning Data Transport (LDT)) protocol. The specifications for the HyperTransport
protocol are open and readily available. [8]
Figure 3: HyperTransport bus layout showing silkscreen information
The primary difficulties in tapping the HyperTransport bus are its high speed (200
MHz DDR) and its use of differential signaling (few logic analyzers come with support
for differential signaling). It is interesting to note that HyperTransport bus protocol
7 7
7 Page 8 9
analyzers are commercially available from vendors such as FuturePlus, but they cost
upward of $25,000. This price does not include the high-end logic analyzer required to
drive the protocol analyzer.
The alternative solution to tapping the northbridge-southbridgeHyperTransport bus
was to build a relatively cheap, fully custom, differential-to-single-ended "Tap Board",
and to connect the output of this board to an FPGA. A Xilinx Virtex-E part was used in
this study because it was readily available, as it was used as part of the author's thesis
work; however, a better choice would be any of the new Xilinx Virtex-II FPGAs. A
suitable Virtex-II FPGA would cost about $50 in single quantities.
The custom Tap Board uses a two-layer, 6 mil trace/ space, 15 mil hole process from
Advanced Circuits, offered at a price of $33 per board in small quantities. A Texas
Instruments SN65LVDS386 LVDS-to-TTL converter was used to turn the differential
HyperTransport signals into a single-ended format. It turns out that the HyperTransport
physical signaling specification is similar to LVDS, but with a different common-mode
offset. The output of the converter drives a cable to the FPGA board. The FPGA
is configured to receive the high speed signals with the CTT (Center-Tap Terminated)
"Select I/ O" option. CTT is chosen because it allows the single-ended TTL drivers to be
terminated with a low impedance to 1. 5V and still function properly. Note that although
Virtex-E FPGAs support LVDS directly, the target FPGA board was not originally
designed to support the LVDS configuration.
12 mil
13 mil
12 mil
differential signal pair
6 mil
trace
Figure 4: Dimensions of the HyperTransport signal traces on the motherboard.
The Tap Board has on one edge a pattern of traces with no soldermask that matches
the pattern of traces on the Xbox motherboard. The Tap Board was soldered directly
to the Xbox's northbridge-southbridge bus. Only the receive-direction Tap Board was
mounted for this study. The mating edge was shaped using a belt sander, so that the
tapping traces were flush with the edge of the board, and the board could be mounted
at a reclined angle to enhance solderability. The soldermask on the Xbox was removed
with fine-grit sand paper, and the Tap Board was carefully aligned by hand, and then
held roughly in place by soldering a coarse piece of wire between the Tap Board and the
motherboard. A hard-setting adhesive, such as Miller-Stephenson Epoxy 907, was ap-plied
to fix the angle and mating distance of the Tap board to the motherboard; once the
epoxy was cured, the holding wire was removed, and the traces between the Tap Board
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and the Xbox motherboard were easily soldered using a fine-tip iron and a microscope.
Figure 5: Tap Board connected to the FPGA board. The FPGA board was originally
developed by the author for another work.
The polarity of the HyperTransport bus signals was determined by probing the idle
state of the wires, assuming that their idle state had a value of 0x00. Those signals that
had the positive and negative pairs swapped relative to the Tap board layout idled to
a "1". Signals with inverted polarity were restored to their true value within the trace
capture FPGA.
Figure 6: Close-up of the Tap Board mounted in the Xbox
A Xilinx Virtex-E FPGA was used to capture traces of HyperTransport bus activ-ity.
It was difficult getting the FPGA to manage the 200 MHz DDR data rates with
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low skew. However, careful hand-layout of the input registers, post-layout timing sim-ulations
at nominal temperature and voltage, and iterations to manually tweak delays
and skews eventually centered the clock signal within the data signal on the FPGA's
input registers. The retimed data was then demultiplexed to a very manageable 100
MHz single-data rate 32-bit wide bus and written into a bank of FIFOs, along with
a sequence count that recorded at what cycle relative to a reset signal the data was
captured. Some additional logic was incorporated into the FPGA that discarded idle
values (0x0000 0000) from the trace FIFOs and formatted the deserialized data relative
to the strobe signal, clearly identified on the Xbox motherboard as "RXD8 / RXD* 8"
(figure 3) in sector 5D (the Xbox motherboard has a coordinate system printed on its
periphery).
The reset signal can be determined by probing traces near the HyperTransport bus
that behaved like a reset signal. In reality, it is possible that some signal that was not
the true reset signal was used to trigger the trace capture, but that is irrelevant as the
signal chosen seemed to display a consistent timing relationship with respect to the
bus. In fact, the signal used to trigger the trace capture exhibited a 350 ns runt pulse
about 67 ms after power-on-reset; this runt pulse was filtered out by a state machine,
as it was erroneously restarting the trace capture.
Once traces of data were captured by the FPGA, the order of the bits on the Hy-perTransport
bus relative to the Tap Board layout could be determined. This can be
done by correlating known values in the FLASH ROM with data values captured on
the HyperTransport bus. A 1's count can be used to identify candidate patterns and
data sequences for manual correlation. Fortunately, very early on in the trace several
distinctive, sequential values are grabbed from the FLASH ROM: a few values from
the lowest address in FLASH ROM, followed by a few values from the boot vector,
which happens to be identical between the decoy FLASH ROM contents and the secret
boot ROM contents. The order of the traces for the receive-direction bus on the moth-erboard
are believed to be, from the outside to the inside, bit 8 (CTL strobe), 4#, 0#,
7#, 2#, 3#, CLK#, 5, 6#, and 1#. Signals with # after them are inverted with respect to
the Tap Board layout.
The raw trace data captured by the FPGA was then dumped to files and manually
processed. An example illustrating the format of trace data can be found in figure 7.
The sequence number was critical in determining the boundaries of cache traces; blocks
of 8 or 16 words are fetched by the processor, even when the caches are off. Trace data
was differentiated between secret boot code and FLASH ROM data by searching for
the first word of the candidate trace in a dump of the FLASH ROM; if the data could
not be found in the FLASH ROM, it was guessed to be secret boot code. Because the
processor boots with its caches off, the first roughly 24 million bus cycles contained
repeated line fills of the "jam table" initialization code, and were ignored as they just
performed the wrote initialization of the chipsets. The caches were then turned on
by the boot code, and very clear and simple to read blocks of instructions and data
were found. These instruction traces were mapped into the secret boot block using
the decoy FLASH ROM boot block as a template. The recovered block of code was
then disassembled, and the decryption algorithm was determined to be 128-bit RC-4.
Because the location of the 128-bit key within the secret boot block was ambiguous
(the Tap Board only provides data traces without addresses), a brute-force search was
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00000097 : 664A1D55
00000D5C : 05F108F6
00000DE0 : 2A1A2841
00000E5D : B6FE7F68
00000EDA : 5932C662
00000F57 : F9FBA4C1
00000FD4 : F7F9B6AE
00001051 : 73376133
000010CE : FD0127AD
0000114B : 34E8FD29
00001245 : 1814A022
000012C2 : 38EBD672
00022526 : C6C0847E
00022527 : A26216BB
00022528 : 99DA5F80
00022529 : 453862E3
000226D5 : B6DF18C0
000226D6 : DA562768
000226D7 : 0F1D66E3
000226D8 : DDC59B59
Figure 7: An example illustrating the format of trace data captured by the FPGA.
Format of the data is "sequence : data
utilized to help isolate the key. A 16-byte sliding "guess key" window over the captured
data trace was used as input to an RC-4 decryption engine, and a histogram of the data
output was used to determine when the key was found. This information helped resolve
some ambiguities in the placement of the data within the secret boot block, and a full
picture of the important code within the secret boot block was assembled.
Now that the secret boot procedure is understood, it is possible to encrypt a new
ROM for the Xbox console, and to further study the structure of the Xbox bootloader
and kernel. Given the RC-4 algorithm, the 128-bit key, and the magic check number at
the end of the decrypted segment, one can run original code on the Xbox.
4 Lessons Learned
One lesson of this study is that the use of a high-performance bus alone is not a suf-ficient
security measure; the advent of cheap, fast rapid prototyping services and high
performance FPGAs allows even poor students to create devices that can tap the bus.
However, encrypting a bus introduces its own problems. A secure cipher on a high per-formance
bus significantly impacts latency, power consumption, and reliability. Power
consumption is increased because the activity factor for the bus approaches 100%, if
the encryption scheme is any good. In this case, the power consumed driving the bus
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would increase by over an order of magnitude, as the observed activity factor on the
northbridge-southbridge bus was well below 10%. Reliability is hurt because a single
bit error, even during an idle cycle, can corrupt large blocks of data; with a stream
cipher, the corruption would extend until the stream is resynchronized.
A compromise solution to the problem is to simply not trust any bus in the system.
In this case, the secret boot block might employ a digital signature protocol, such as
Authenticode R , using public key algorithms and one-way hashes. [10] Then, all secu-rity
rests in the secrecy of the private key, and the strength of the public key algorithm.
In order to prevent employee leaks from spreading a private key, a system similar to the
BBN SignAssure TM could be used to manage the key so that no human ever has knowl-edge
of the private key. The principal drawback of this method is that it requires extra
silicon area to be spent on storing a larger secret boot block, as it is probably difficult,
if not impossible, to code a full public key encryption algorithm plus key storage and
hardware initialization code within 512 bytes.
The above suggestion does not prevent someone from eavesdropping and obtaining
the plaintext of the operating system code, but it does effectively defeat any attempt
to run original code. The public key scheme could be defeated, however, by a mech-anism
that snoops the main memory bus and patches plaintext in main memory. As
discussed previously, this approach is possible, but difficult; however, the tenacity of
an attacker should not be underestimated. For example, a known attack on the Sony
Playstation2 console was developed that is rumored to work by dynamically patching
its high-performance RAMBUS memory system. The difficulty of a memory patch at-tack
could be increased by using a simple periodic hash and check of the critical code
regions in memory.
Buffer overrun exploits are also a point of weakness, and they work regardless of
the secret boot protocol. An attacker sniffing an insecure bus could obtain the de-crypted
kernel code and analyze it for weaknesses. However, any machine architecture
that employs guarded pointers [11] is much more difficult, if not impossible, to attack
using buffer overruns. A fast, efficient guarded pointer scheme with a simple hardware
implementation is described in [12]. This scheme can easily be adapted to work in a
64-bit architecture.
A. Kerckhoffs (1835-1903) once stated that the security of a cryptosystemmust not
depend on keeping the algorithmsecret; this is referred to as Kerckhoffs' Principle.[ 13]
Another way of stating this is that there is no security through obscurity. In particular,
it is an error to assume that a secret, distributed along with the information it guards, is
never revealed. For example, the Sega Dreamcast uses a proprietary GD-ROMsoftware
format; but, the drive can read CD-ROM disks. The discovery of a back door in the
Dreamcast OS allowed executables to be run directly from a standard CD-ROM, thus
nullifying the barrier presented by the proprietary GD-ROMformat. Other systems that
rely on well-hidden secrets, including the Clipper chip [14] and the smartcards used
widely throughout Europe to control access to services such as pay-TV, cell phones and
gas, have been shown to be surprisingly vulnerable. [15] In this case, the Tap Board
and trace capture FPGA design was developed in spare time over the duration of three
weeks- including the 5-day turn time for board fabrication- for a total cost of around
$50 per board. In other words, if you ship your secrets in your hardware, it is a good
assumption that the users will eventually- and perhaps quickly- know your secrets.
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The failure of the Microsoft Xbox console security protocol is compounded by the
fact that, as a console manufacturer, design-for-test and design-for-manufacturability
is paramount. Creating a console with too much security makes it difficult to debug
and manufacture. For example, the backside of the Xbox motherboard is populated
with test points- including test points for every pin on the FLASH ROM. These were
originally installed because of the desire to quickly test for faults during manufactur-ing.
The flip side is that one could build a custom "bed-of-nails" tester jig that uses the
the FLASH-ROM test points to reprogram Xbox motherboards with any desired code.
This method would be fast, inexpensive and solder-free. The lesson here is that even if
a manufacturer is very confident about their trust model and security protocols, it must
guard against the possibility that they may someday be broken. To this extent, a sim-ple
physical security measure, such as a spray-on conformal coating, would severely
hamper the re-use of test structures for improper purposes. This of course greatly com-plicates
the repair of hardware failures in the field, but that is a business trade-off the
manufacturer must make.
A more radical alternative would be to design the gaming system using proprietary
hardware and proprietary media formats, thus limiting the practical impact of any at-tack
on the console. Game consoles are manufactured in very high volumes, so the cost
of developing a simple but effective proprietary format can be amortized. The format
could then be patented, providing protection against unauthorized use without the need
for secrecy. This approach was taken by Nintendo with their Nintendo 64 console. [16]
Although patents have a 20 year lifetime, this is an eternity in the video game console
industry: the original Nintendo Entertainment System (NES) had its debut in 1985.
5 Future Work
Understanding the secret Xbox boot protocol is just the first step in understanding
the Xbox. It is now possible to investigate the kernel and bootloader in more detail.
It has been determined that the kernel is also encrypted with RC-4/ 128, and it is also
believed to be compressed using LZX compression, a scheme employed by Microsoft's
canonical distribution format, the "Cabinet" file. The structure and function of the
kernel is still being investigated.
One important issue to investigate is the privacy of users who use the Xbox for on-line
tasks. It is known, through a parallel effort of the author, that information such as
the serial number of the console is stored electronically and is probably accessible to the
kernel. What happens to this information when the Xbox is plugged into the internet?
Because of the encryption used to secure the Xbox, the nature of the information that is
relayed to Microsoft's on-line game servers is unknown. Thus, important future work is
to try to determine what the Xbox reveals about the user's identity and personal gaming
habits.
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6 Addendum
It has recently been called to the author's attention that the hardware initialization pro-cedure
of the Xbox contains a significant weakness. [17] Recall from section 2 that
the first step in the Xbox boot process is to load the "jam tables" that configure the
console's chipsets. This jam table initialization procedure involves a lengthy and com-plex
sequence of writes to various memory-mapped hardware register locations. As a
result, the initialization procedure is implemented using a simple bytecode interpreter
that reads initialization commands and data from the FLASH ROM. These bytecode
commands- stored as plaintext- can be manipulated to cause the initialization procedure
to abort before the kernel decryption/ verification routine is executed, and to instead run
insecure code directly out of the FLASH ROM. In other words, with plaintext-only
modifications in the FLASH ROM, one can entirely bypass the Xbox's security mech-anism.
One could easily fix this security hole, however, by verifying the jam table's
contents prior to bytecode execution with a one-way hash function, or by explicitly
coding all initialization functions within the secure boot block. Both of these solutions,
however, would require the secure boot block to grow significantly from its current
512-byte size, and neither solution allows easy changes to the initialization procedure
in case a bug is found or in case the hardware evolves as a result of cost reduction
efforts.
Acknowledgments
The author would like to acknowledge the support of the on-line electronic community.
The author would also like to thank the Electronic Frontier Foundation for providing
legal counsel. Hal Abelson and Tom Knight also provided invaluable moral support.
Finally, the author would like to thank Nikki Justis for all her love and support, and for
giving him such an interesting toy for Christmas.
References
[1] Federal Information Processing Standards Publication, FIPS PUB 185: Escrowed
Encryption Standard (EES) http:// www. itl. nist. gov/ fipspubs/ fip185. htm
[2] Thomas W. Krygowski, Jeffry J. Sniegowski, M. Steven Rodgers, Stephen
Montague, James J. Allen, Jerome F. Jakubczak, Samuel L. Miller, Infras-tructure,
Technology and Applications Of Micro-Electro-Mechanical Systems
(MEMS), Sandia National Laboratories, Intelligent Micromachine Department,
http:// www. mdl. sandia. gov/ Micromachine, also appears in Sensor Expo 1999.
[3] IBM, IBM 4758 PCI Cryptographic Coprocessor,
http:// www. ibm. com/ security/ cryptocards/
[4] Gemplus (a smartcard vendor), Gemplus Corporate Website,
http:// www. gemplus. com
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[5] Pil Joon Lee, Eun Jeong Lee, Yong Duk Kim, How to Implement Cost-Effective
and Secure Public Key Cryptosystems Proceedings of the First International Work-shop
on Cryptographic Hardware and Embedded Systems (CHES), August 1999.
[6] Federal Information Processing Standards Publication, FIPS
PUB 140-2: Security Requirements for Cryptographic Modules,
http:// csrc. nist. gov/ publications/ fips/ fips140-2/ fips1402.pdf
[7] distributed. net, distributed. net: Project RC5, http:// www. distributed. net/ rc5/
[8] HyperTransport Consortium, HyperTransport TM I/ O Link Specification, Version
1.03, http:// www. hypertransport. org
[9] nVidia Corporation, nForce MCP Product Overview, 06.01v1,
http:// www. nvidia. com
[10] Microsoft Developer Network, Introduction to Code Signing,
http:// msdn. microsoft. com/ workshop/ security/ authcode/ intro authenticode. asp
[11] Nicholas P. Carter, Stephen W. Keckler, and William J. Dally, Hardware support
for fast capability-based addressing, Proceedings of ASPLOS VI, October 1994,
pp. 319-27.
[12] Jeremy Brown, J. P. Grossman, Andrew Huang, and Thomas F.
Knight, Jr., A capability representation with embedded address
and nearly-exact object bounds, Project Aries Technical Memo 5,
http:// www. ai. mit. edu/ projects/ aries/ Documents/ Memos/ ARIES-05. pdf
[13] Auguste Kerckhoffs, La cryptographie militaire, Journal des sciences militaires,
vol. IX, pp. 5-38, Jan. 1883, pp. 161-191, Feb. 1883.
[14] R. Anderson and M. Kuhn, Tamper Resistance -a Cautionary Note, Proceedings
of the Second Usenix Workshop on Electronic Commerce, pp. 1- 11, November
1996.
[15] R. Anderson and M. Kuhn, Low Cost Attacks on Tamper Resistant Devices,
IWSP: International Workshop on Security Protocols, LNCS, 1997.
[16] Van Hook, et al., High Performance Low Cost Video Game System with Co-processor
Providing High Speed Efficient 3D Graphics and Digital Audio Signal
Processing, U. S. Patent 6, 239,810, May 29, 2001.
[17] Private conversation with visor. visor can be reached by sending a personal mes-sage
to visor on www. xboxhacker. net
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The space shuttle is well armored. Yet when the thing was origionally designed, nobody knew how common high velocity (but tiny) rocks would be up there. It turned out that the shuttle had insufficient armor to deal with micrometeorites for very long. That is why you see clips of the shuttle 'flying backwards' while in orbit. There is more armor on that side...
"(a) Photons are massless, so you can't use newtonian gravity F=GmM/r^2 to compute gravitation effects on it.
:>
I trust that you are not saying that light is not affected by gravity? The mass of photons is debatable, but it is a well known, observed fact that light is indeed affected by gravity."
It is indeed observed. In fact, this was one of the first things that 'proved' the Theory of Relativity. An expedition to Africa was made to observe the sun during an eclipse. If photons were affected by gravity, then the light passing near the sun (which is normally drowned out by the sun's light, but isn't drowned out during an eclipse) would be distorted. Well, the distortion was observed.