Xbox360TimingAttack

De ElOtroLado

El 'Timing Attack' se usa para permitir el downgrade de maquinas con kernel 4552 o superior. El proposito del 'timing attack' es encontrar el valor requerido de hash para permitir que un kernel base (1888) con la seccion CB alterada sea arrancado por la consola. El contador 'lockdown' (contador de efuses quemados) de la seccion CB es cambiado a un valor mas alto para permitir que un kernel base (1888) pueda ser arrancado en una consola con efuses quemados. Esta comprobacion es, basicamente, lo que hace imposible reflashear la NAND con un kernel mas antiguo (o vulnerable).

La comunidad de XboxHacker.net hizo este proyecto posible. Arnezami encontro el vector del 'timing attack' e imagino el concepto basico, y Robinsod construyo el hardware necesario para el downgrade y el software de medicion requerido para realizar el ataque.

Contenido: [hide]

   * 1 Purpose
   * 2 Memcmp Flaw
   * 3 Procedure
         o 3.1 Dump NAND
         o 3.2 Patch CB
         o 3.3 Flash Image
         o 3.4 Attack Hash
         o 3.5 Upgrade Kernel
         o 3.6 Get CPU Key
   * 4 Results
   * 5 Speculation
   * 6 References

[edit]

Proposito:

Una buena explicacion de arnezami [1]:

¿[Con la CPU Key] no podemos refirmar las partes esenciales del hipervisor (de ahora en adelante HV), o cualquier otra cosa, con un bootloader modificado? Todo el codigo ejecutable en la Xbox esta (de una u otra forma) firmado con una clave RSA. MS tiene la clave privada RSA, y esa es la razon por la cual nunca sera posible firmar nuestro propio codigo. Esto es lo que nos impide ejecutar cualquier cosa diferente de lo que MS ha compilado/firmado (como el Kernel o el bootloader). Esto no tiene nada que ver con la CPUKey, la unica cosa que podemos hacer con la CPUKey es elegir que version del Kernel/bootloader queremos ejecutar, pero no podemos cambiar ni un bit a ninguno de ellos.

Entonces... ¿Porque downgradear? Porque dos versiones de kernel que MS ha publicado (4532 y 4548) tienen un pequeño fallo. Y si tenemos nuestra CPUKey podemos ejecutar dichas (viejas) versiones de Kernel y 'explotarlas' ejecutando el juego KingKong (de ahora en adelante, KK) parcheado especialmente. Despues de ejecutar el exploit del juego KK, tenemos control total sobre la Xbox (pero no antes). Esto significa que para poder ejecutar software casero o linux, necesitas iniciar el juego, presionar OK, insertar un disco, etc...

Representacion Visual del proceso a seguir:

Memcmp Flaw

A memcmp function is used to check the CB-auth HMAC-hash value. The value is 16-bytes long and is done byte-by-byte wise. By changing one byte at a time it's possible to determine if a byte is the valid (true) by measuring the time to compare a false and a true value. Measuring each byte will in the end reveal the correct hash and the boot process can continue.

The time differences for a valid and false value is about 2200 microseconds.

Possibilities: 16 bytes * 256 different possibility for each byte, total 4096 tries. Statistically only half has to be tried, 2048 tries. [edit] Procedure

The official documentation by robinsod for the downgrader hardware and downgrading process can be downloaded from the Timing Attack thread over at XboxHacker. [edit] Dump NAND

Use Infectus or custom hardware (memorycard reader) to make a valid dump of the current NAND.

   * Xbox 360 Infectus Kernel Dump 

Image:Infectus Read NAND.PNG [edit] Patch CB

Get a plain 1888 base kernel and patch the CB lockdown counter with the LDV (LockDownValue) from the CF section in the NAND dump.

  1. Get the 1888 base kernel from the "usual places".
  2. Download Degraded.exe to automate the build of a new 1888 image with the SMC, Keyvault, CB, CD and CE sections from the NAND dump. The LDV (fuse count) will be corrected for CB (which is why you need to find a new hash) and the hash value is set to all zeroes. 

An external 1888 base kernel is needed because essential system files for 1888 is overwritten in the 4552 update and later, making it impossible to use the NAND dump to create a new 1888 image.

In Degraded.exe click 'Settings', set the 1BL Key to 'DD88AD0C9ED669E7B56794FB68563EFA', select the folder where the 1888 file system is located, and set 'File System Start' to '39'.

Image:Timing attack degraded settings.PNG

Select the NAND dump file under 'Flash Dump' and click 'Build Downgrader Image'.

Image:Timing attack degraded.PNG

   * Downgrading Tools 

[edit] Flash Image

Flash the new 1888 base kernel build to the NAND.

Connect Infectus chip to the Xbox 360 again, erase and flash the new patched 1888 base kernel image.

   * Xbox 360 Infectus Kernel Dump 

Image:Infectus Write NAND.PNG [edit] Attack Hash

Attack the HMAC-hash value using the timing hardware and DGTool.

  1. Build the downgrader hardware and connect a serial port cable and power/ground (3.3v or 5v) from the 360 or an external power supply (USB) to the downgrader hardware.
  2. Connect the USB cable to the Infectus chip. The Infectus is required to flash the NAND page for the CB section with a new value for each new guess (every ~2 seconds).
  3. Create a folder with the 3 following files; DGTool.exe, Infectus.dll and SiUSBXp.dll. Move the 1888 image to this folder too, e.g. Infectus_5787_downgraded_1888.bin.
  4. Open a new command-prompt, by Start -> Run -> 'cmd'. Change directory (cd) to the folder where the DGTool.exe is located.
  5. DGTool normally only needs 2 arguments to start; one being the COM- or serial port the downgrader hardware is connected to and the other is the filename of the patched 1888 image. 

DGTool.exe 1 Infectus_5787_downgraded_1888.bin

Enter the command above and press enter. Now power on the Xbox 360 and wait for the 3 red lights to start blinking, aka Red Ring Of Death (RROD). Press enter once more to start the timing process. Let it run for a little over an hour (around 1 hour 10 minutes seems to be normal) and the correct hash value will hopefully be discovered. If successful the last line of text should state 'BOOT!'.

   * Xbox 360 Downgrader Hardware 

Image:Timing attack dgtool.PNG [edit] Upgrade Kernel

Once you can boot the 1888 base kernel, you can apply the vulnerable 4532 or 4548 update to use the King King exploit.

Download the 4532 HD DVD update, extract the files into a folder, and burn the content on a regular CD-R. Insert the CD-R into the Xbox 360 and you will be prompted that a update is required.

Image:Timing attack 1888 boot success.jpg

Image:Xbox 4532 Kernel.JPG [edit] Get CPU Key

Boot a modified King Kong game disc and launch Gentoo Linux to get the CPU Key.

  1. Patch the King Kong game image with the King Kong exploit and burn it to a DVD+R Dual Layer disc.
  2. Burn the latest Gentoo Xenon release (as of writing beta2) from free60.org to a CD-R and insert the disc after pressing 'Start' on the modified King Kong disc.
  3. Download the dump32 application to dump the fusesets to find the CPU Key of the machine. 

wget http://home.x-pec.com/~ivc/sites/ivc/xbox360/files/arnezamidump32.tgz tar zxvf arnezamidump32.tgz cd arnezamidump32 sudo ./dump32

Image:Dump32 Finished and List.png

Save the FUSES.TXT file to a USB memorystick, upload it to yousendit.com, mail it to yourself, or use the 'scp' or 'ftp' utility to transfer it over the network to a computer.

The CPU Key is found by combining line 3 + 5 in the FUSES.TXT file.

It is now possible to upgrade to latest kernel (as of writing 5787) and then downgrade to a lower version again using the 360 Flash Tool. Insert the correct CPU Key in the 360 Flash Tool and patching the LDV (LockDownValue) in the CB/CE/CF section to that of the latest update.

   * Xbox 360 Kernel
   * Xbox 360 King Kong Shader Exploit 

[edit] Results

All of my runs can be found on the page below.

   * Xbox 360 Timing Attack Results 

[edit] Speculation

arnezami:

MS cannot fix this problem by simply changing the memcmp function in a future kernel version. Thats not gonna help them. The weakness is that the byte-wise memcmp function is in the 1888 kernel/bootloader (and they cannot change that one anymore of course). [2]

tmbinc:

sure, microsoft can change the 2BL, and burn a fuse (of the fuseline 2) so that an old 2BL doesn't work anymore... [3]

arnezami:

Ah. Right. If they can indeed burn these fuses at row 2 than you wouldn't be able to run any of the lower kernel versions anymore. [4]

Been thinking about this. I'm now pretty sure when row 2 of the fuses is burned your xbox won't be able to downgrade or run homebrew anymore (it appears the fuse count number is indeed RSA signed). [5]

surrido:

you could if it makes you happy wire a switch to the R6T3 and keep it on while being in live and turn it of when you receive an update. [6]

tmbinc:

No, a switch at R6T3 doesn't help. It's not the resistor which presence can be detected, but the result to the fuse (burned or not).

So his question is completely valid: If you remove the resistor, you could end up with an unbootable box after the next update. But at least you could restore a previous flash. (If you want, you could *then* re-attach the resistor, and update again, of course loosing the possibility to downgrade). [7]

[edit] References

• Fuente original: http://beta.ivancover.com/wiki/index.php/Xbox_360_Timing_Attack

• Timing Attack
• Timing Attach - Thanks and stupid questions