Part 2, Topic 2: Introduction to Voltage Glitching (MAIN)¶
SUMMARY: While it’s not as sophisticated as the ChipWhisperer Lite or ChipWhisperer Pro’s glitch hardware, the ChipWhisperer Nano is also capable of glitching. In this lab, we’ll do some simple glitch tests on the Nano’s target board, showing how to scan through glitch settings and seeing what effect it has on the hardware.
LEARNING OUTCOMES:
Understanding how voltage glitching can be used to disrupt a target’s operation
Scanning glitch settings to determine successful ones
Digital hardware devices have certain voltage and clock requirements to
function properly. If these requirements are not met, the device can
fail to function, or even be damage. By shorting the voltage pins of a
microcontroller for controlled, short periods of time, we can cause it
to behave erratically, clearning registers and skipping instructions.
Such attacks can be immensely powerful in practice. Consider for example
the following code from linux-util-2.24:
/*
* auth.c -- PAM authorization code, common between chsh and chfn
* (c) 2012 by Cody Maloney <cmaloney@theoreticalchaos.com>
*
* this program is free software. you can redistribute it and
* modify it under the terms of the gnu general public license.
* there is no warranty.
*
*/
#include "auth.h"
#include "pamfail.h"
int auth_pam(const char *service_name, uid_t uid, const char *username)
{
if (uid != 0) {
pam_handle_t *pamh = NULL;
struct pam_conv conv = { misc_conv, NULL };
int retcode;
retcode = pam_start(service_name, username, &conv, &pamh);
if (pam_fail_check(pamh, retcode))
return FALSE;
retcode = pam_authenticate(pamh, 0);
if (pam_fail_check(pamh, retcode))
return FALSE;
retcode = pam_acct_mgmt(pamh, 0);
if (retcode == PAM_NEW_AUTHTOK_REQD)
retcode =
pam_chauthtok(pamh, PAM_CHANGE_EXPIRED_AUTHTOK);
if (pam_fail_check(pamh, retcode))
return FALSE;
retcode = pam_setcred(pamh, 0);
if (pam_fail_check(pamh, retcode))
return FALSE;
pam_end(pamh, 0);
/* no need to establish a session; this isn't a
* session-oriented activity... */
}
return TRUE;
}
This is the login code for the Linux OS. Note that if we could skip the
check of if (uid != 0) and simply branch to the end, we could avoid
having to enter a password. This is the power of glitch attacks - not
that we are breaking encryption, but simply bypassing the entire
authentication module!
Glitch Hardware¶
The ChipWhisperer Nano’s glitch setup is pretty simple. Like its bigger brothers, the Lite and the Pro, it uses a MOSFET to short the microcontroller’s voltage supply to ground:
For the Nano, Glitch In is controlled by 2 parameters:
scope.glitch.ext_offset- The glitch will be inserted roughly8.3ns * scope.glitch.ext_offsetscope.glitch.repeat- The glitch will be inserted for roughly8.3ns * scope.glitch.repeat
During this lab, we’ll be varying these parameters to see if we can get the target to mess up a calculation that it’s doing.
In [1]:
SCOPETYPE = 'CWNANO'
PLATFORM = 'CWNANO'
In [2]:
%%bash -s "$PLATFORM"
cd ../../../hardware/victims/firmware/simpleserial-glitch
make PLATFORM=$1 CRYPTO_TARGET=NONE
Out [2]:
SS_VER set to SS_VER_1_1 rm -f -- simpleserial-glitch-CWNANO.hex rm -f -- simpleserial-glitch-CWNANO.eep rm -f -- simpleserial-glitch-CWNANO.cof rm -f -- simpleserial-glitch-CWNANO.elf rm -f -- simpleserial-glitch-CWNANO.map rm -f -- simpleserial-glitch-CWNANO.sym rm -f -- simpleserial-glitch-CWNANO.lss rm -f -- objdir/*.o rm -f -- objdir/*.lst rm -f -- simpleserial-glitch.s simpleserial.s stm32f0_hal_nano.s stm32f0_hal_lowlevel.s rm -f -- simpleserial-glitch.d simpleserial.d stm32f0_hal_nano.d stm32f0_hal_lowlevel.d rm -f -- simpleserial-glitch.i simpleserial.i stm32f0_hal_nano.i stm32f0_hal_lowlevel.i . Welcome to another exciting ChipWhisperer target build!! arm-none-eabi-gcc.exe (GNU Arm Embedded Toolchain 9-2020-q2-update) 9.3.1 20200408 (release) Copyright (C) 2019 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. . Compiling C: simpleserial-glitch.c arm-none-eabi-gcc -c -mcpu=cortex-m0 -I. -mthumb -mfloat-abi=soft -ffunction-sections -gdwarf-2 -DSS_VER=SS_VER_1_1 -DSTM32F030x6 -DSTM32F0 -DSTM32 -DDEBUG -DHAL_TYPE=HAL_stm32f0_nano -DPLATFORM=CWNANO -DF_CPU=7372800UL -Os -funsigned-char -funsigned-bitfields -fshort-enums -Wall -Wstrict-prototypes -Wa,-adhlns=objdir/simpleserial-glitch.lst -I.././simpleserial/ -I.././hal -I.././hal/stm32f0 -I.././hal/stm32f0/CMSIS -I.././hal/stm32f0/CMSIS/core -I.././hal/stm32f0/CMSIS/device -I.././hal/stm32f0/Legacy -I.././crypto/ -std=gnu99 -MMD -MP -MF .dep/simpleserial-glitch.o.d simpleserial-glitch.c -o objdir/simpleserial-glitch.o . Compiling C: .././simpleserial/simpleserial.c arm-none-eabi-gcc -c -mcpu=cortex-m0 -I. -mthumb -mfloat-abi=soft -ffunction-sections -gdwarf-2 -DSS_VER=SS_VER_1_1 -DSTM32F030x6 -DSTM32F0 -DSTM32 -DDEBUG -DHAL_TYPE=HAL_stm32f0_nano -DPLATFORM=CWNANO -DF_CPU=7372800UL -Os -funsigned-char -funsigned-bitfields -fshort-enums -Wall -Wstrict-prototypes -Wa,-adhlns=objdir/simpleserial.lst -I.././simpleserial/ -I.././hal -I.././hal/stm32f0 -I.././hal/stm32f0/CMSIS -I.././hal/stm32f0/CMSIS/core -I.././hal/stm32f0/CMSIS/device -I.././hal/stm32f0/Legacy -I.././crypto/ -std=gnu99 -MMD -MP -MF .dep/simpleserial.o.d .././simpleserial/simpleserial.c -o objdir/simpleserial.o . Compiling C: .././hal/stm32f0_nano/stm32f0_hal_nano.c arm-none-eabi-gcc -c -mcpu=cortex-m0 -I. -mthumb -mfloat-abi=soft -ffunction-sections -gdwarf-2 -DSS_VER=SS_VER_1_1 -DSTM32F030x6 -DSTM32F0 -DSTM32 -DDEBUG -DHAL_TYPE=HAL_stm32f0_nano -DPLATFORM=CWNANO -DF_CPU=7372800UL -Os -funsigned-char -funsigned-bitfields -fshort-enums -Wall -Wstrict-prototypes -Wa,-adhlns=objdir/stm32f0_hal_nano.lst -I.././simpleserial/ -I.././hal -I.././hal/stm32f0 -I.././hal/stm32f0/CMSIS -I.././hal/stm32f0/CMSIS/core -I.././hal/stm32f0/CMSIS/device -I.././hal/stm32f0/Legacy -I.././crypto/ -std=gnu99 -MMD -MP -MF .dep/stm32f0_hal_nano.o.d .././hal/stm32f0_nano/stm32f0_hal_nano.c -o objdir/stm32f0_hal_nano.o . Compiling C: .././hal/stm32f0/stm32f0_hal_lowlevel.c arm-none-eabi-gcc -c -mcpu=cortex-m0 -I. -mthumb -mfloat-abi=soft -ffunction-sections -gdwarf-2 -DSS_VER=SS_VER_1_1 -DSTM32F030x6 -DSTM32F0 -DSTM32 -DDEBUG -DHAL_TYPE=HAL_stm32f0_nano -DPLATFORM=CWNANO -DF_CPU=7372800UL -Os -funsigned-char -funsigned-bitfields -fshort-enums -Wall -Wstrict-prototypes -Wa,-adhlns=objdir/stm32f0_hal_lowlevel.lst -I.././simpleserial/ -I.././hal -I.././hal/stm32f0 -I.././hal/stm32f0/CMSIS -I.././hal/stm32f0/CMSIS/core -I.././hal/stm32f0/CMSIS/device -I.././hal/stm32f0/Legacy -I.././crypto/ -std=gnu99 -MMD -MP -MF .dep/stm32f0_hal_lowlevel.o.d .././hal/stm32f0/stm32f0_hal_lowlevel.c -o objdir/stm32f0_hal_lowlevel.o . Assembling: .././hal/stm32f0/stm32f0_startup.S arm-none-eabi-gcc -c -mcpu=cortex-m0 -I. -x assembler-with-cpp -mthumb -mfloat-abi=soft -ffunction-sections -DF_CPU=7372800 -Wa,-gstabs,-adhlns=objdir/stm32f0_startup.lst -I.././simpleserial/ -I.././hal -I.././hal/stm32f0 -I.././hal/stm32f0/CMSIS -I.././hal/stm32f0/CMSIS/core -I.././hal/stm32f0/CMSIS/device -I.././hal/stm32f0/Legacy -I.././crypto/ .././hal/stm32f0/stm32f0_startup.S -o objdir/stm32f0_startup.o . Linking: simpleserial-glitch-CWNANO.elf arm-none-eabi-gcc -mcpu=cortex-m0 -I. -mthumb -mfloat-abi=soft -ffunction-sections -gdwarf-2 -DSS_VER=SS_VER_1_1 -DSTM32F030x6 -DSTM32F0 -DSTM32 -DDEBUG -DHAL_TYPE=HAL_stm32f0_nano -DPLATFORM=CWNANO -DF_CPU=7372800UL -Os -funsigned-char -funsigned-bitfields -fshort-enums -Wall -Wstrict-prototypes -Wa,-adhlns=objdir/simpleserial-glitch.o -I.././simpleserial/ -I.././hal -I.././hal/stm32f0 -I.././hal/stm32f0/CMSIS -I.././hal/stm32f0/CMSIS/core -I.././hal/stm32f0/CMSIS/device -I.././hal/stm32f0/Legacy -I.././crypto/ -std=gnu99 -MMD -MP -MF .dep/simpleserial-glitch-CWNANO.elf.d objdir/simpleserial-glitch.o objdir/simpleserial.o objdir/stm32f0_hal_nano.o objdir/stm32f0_hal_lowlevel.o objdir/stm32f0_startup.o --output simpleserial-glitch-CWNANO.elf --specs=nano.specs --specs=nosys.specs -T .././hal/stm32f0_nano/LinkerScript.ld -Wl,--gc-sections -lm -mthumb -mcpu=cortex-m0 -Wl,-Map=simpleserial-glitch-CWNANO.map,--cref -lm . Creating load file for Flash: simpleserial-glitch-CWNANO.hex arm-none-eabi-objcopy -O ihex -R .eeprom -R .fuse -R .lock -R .signature simpleserial-glitch-CWNANO.elf simpleserial-glitch-CWNANO.hex . Creating load file for EEPROM: simpleserial-glitch-CWNANO.eep arm-none-eabi-objcopy -j .eeprom --set-section-flags=.eeprom="alloc,load" --change-section-lma .eeprom=0 --no-change-warnings -O ihex simpleserial-glitch-CWNANO.elf simpleserial-glitch-CWNANO.eep || exit 0 . Creating Extended Listing: simpleserial-glitch-CWNANO.lss arm-none-eabi-objdump -h -S -z simpleserial-glitch-CWNANO.elf > simpleserial-glitch-CWNANO.lss . Creating Symbol Table: simpleserial-glitch-CWNANO.sym arm-none-eabi-nm -n simpleserial-glitch-CWNANO.elf > simpleserial-glitch-CWNANO.sym Size after: text data bss dec hex filename 4740 12 1292 6044 179c simpleserial-glitch-CWNANO.elf +-------------------------------------------------------- + Default target does full rebuild each time. + Specify buildtarget == allquick == to avoid full rebuild +-------------------------------------------------------- +-------------------------------------------------------- + Built for platform CWNANO Built-in Target (STM32F030) with: + CRYPTO_TARGET = NONE + CRYPTO_OPTIONS = +--------------------------------------------------------
In [3]:
%run "../../Setup_Scripts/Setup_Generic.ipynb"
Out [3]:
Serial baud rate = 38400
INFO: Found ChipWhisperer😍
In [4]:
fw_path = "../../../hardware/victims/firmware/simpleserial-glitch/simpleserial-glitch-{}.hex".format(PLATFORM)
cw.program_target(scope, prog, fw_path)
Out [4]:
Serial baud rate = 115200
Detected known STMF32: STM32F03xx4/03xx6
Extended erase (0x44), this can take ten seconds or more
Attempting to program 4751 bytes at 0x8000000
STM32F Programming flash...
STM32F Reading flash...
Verified flash OK, 4751 bytes
Serial baud rate = 38400
In [5]:
scope.io.clkout = 7.5E6
target.baud = 38400*7.5/7.37
def reboot_flush():
scope.io.nrst = False
time.sleep(0.05)
scope.io.nrst = "high_z"
time.sleep(0.05)
#Flush garbage too
target.flush()
Out [5]:
Serial baud rate = 39077.34056987788
In [6]:
scope
Out [6]:
ChipWhisperer Nano Device
fw_version =
major = 0
minor = 11
debug = 0
io =
tio1 = None
tio2 = None
tio3 = None
tio4 = None
pdid = True
pdic = False
nrst = True
clkout = 7500000.0
adc =
clk_src = int
clk_freq = 7500000.0
samples = 5000
glitch =
repeat = 0
ext_offset = 10
In [7]:
reboot_flush()
scope.arm()
target.write("g\n")
scope.capture()
val = target.simpleserial_read_witherrors('r', 4, glitch_timeout=10)#For loop check
valid = val['valid']
if valid:
response = val['payload']
raw_serial = val['full_response']
error_code = val['rv']
print(val)
Out [7]:
{'valid': True, 'payload': CWbytearray(b'c4 09 00 00'), 'full_response': 'rC4090000n', 'rv': 0}
In [8]:
import chipwhisperer.common.results.glitch as glitch
gc = glitch.GlitchController(groups=["success", "reset", "normal"], parameters=["repeat", "ext_offset"])
gc.display_stats()
Out [8]:
Some tips for finding good glitches:
This is a VCC line that we’re shorting, so there’s going to be stuff fighting against us. If your glitch is too short, it might not have any effect
Likewise, if your glitch is too long, the target will always crash. There’s typically a small band where you’re able to affect the target, but it won’t always crash it.
Be patient. Glitching can be somewhat inconsistant, so don’t be discouraged if it takes a while to see some success!
In [9]:
%matplotlib inline
import matplotlib.pylab as plt
fig = plt.figure()
Out [9]:
<Figure size 432x288 with 0 Axes>
In [10]:
from importlib import reload
import chipwhisperer.common.results.glitch as glitch
from tqdm.notebook import trange
import struct
g_step = 1
gc.set_global_step(g_step)
gc.set_range("repeat", 1, 7)
gc.set_range("ext_offset", 1, 200)
scope.glitch.repeat = 0
reboot_flush()
sample_size = 1
for glitch_setting in gc.glitch_values():
scope.glitch.repeat = glitch_setting[0]
scope.glitch.ext_offset = glitch_setting[1]
successes = 0
resets = 0
for i in range(5):
target.flush()
scope.arm()
#Do glitch loop
target.write("g\n")
ret = scope.capture()
val = target.simpleserial_read_witherrors('r', 4, glitch_timeout=10)#For loop check
if ret:
print('Timeout - no trigger')
gc.add("reset", (scope.glitch.repeat, scope.glitch.ext_offset))
plt.plot(scope.glitch.ext_offset, scope.glitch.repeat, 'xr', alpha=1)
fig.canvas.draw()
resets += 1
#Device is slow to boot?
reboot_flush()
else:
if val['valid'] is False:
reboot_flush()
gc.add("reset", (scope.glitch.repeat, scope.glitch.ext_offset))
plt.plot(scope.glitch.ext_offset, scope.glitch.repeat, 'xr', alpha=1)
fig.canvas.draw()
resets += 1
else:
gcnt = struct.unpack("<I", val['payload'])[0]
if gcnt != 2500: #for loop check
gc.add("success", (scope.glitch.repeat, scope.glitch.ext_offset))
print(gcnt)
plt.plot(scope.glitch.ext_offset, scope.glitch.repeat, '+g', alpha=1)
fig.canvas.draw()
successes += 1
else:
gc.add("normal", (scope.glitch.repeat, scope.glitch.ext_offset))
if successes > 0:
print("successes = {}, resets = {}, repeat = {}, ext_offset = {}".format(successes, resets, scope.glitch.repeat, scope.glitch.ext_offset))
print("Done glitching")
Out [10]:
2451 2451 2451 2451 2451 successes = 5, resets = 0, repeat = 1, ext_offset = 121 2451 successes = 1, resets = 2, repeat = 2, ext_offset = 9 2501 2501 2501 successes = 3, resets = 0, repeat = 2, ext_offset = 10 2451 2501 2451 2497 successes = 4, resets = 0, repeat = 2, ext_offset = 17 2501 2451 2501 2501 successes = 4, resets = 0, repeat = 2, ext_offset = 24 2501 2501 2501 2501 2501 successes = 5, resets = 0, repeat = 2, ext_offset = 25 2451 successes = 1, resets = 0, repeat = 2, ext_offset = 28 2451 2501 2501 successes = 3, resets = 1, repeat = 2, ext_offset = 32 2451 2501 2451 2501 successes = 4, resets = 1, repeat = 2, ext_offset = 39 2501 2501 2501 2501 successes = 4, resets = 0, repeat = 2, ext_offset = 43 2501 2501 2501 2501 2501 successes = 5, resets = 0, repeat = 2, ext_offset = 50 2501 2501 2501 2501 2501 successes = 5, resets = 0, repeat = 2, ext_offset = 57 2501 2501 2501 2501 2501 successes = 5, resets = 0, repeat = 2, ext_offset = 58 2451 successes = 1, resets = 3, repeat = 2, ext_offset = 80 2451 2451 successes = 2, resets = 2, repeat = 2, ext_offset = 87 2451 successes = 1, resets = 0, repeat = 2, ext_offset = 90 2451 2451 successes = 2, resets = 3, repeat = 2, ext_offset = 91 2451 2451 2451 2451 2451 successes = 5, resets = 0, repeat = 2, ext_offset = 104 2499 successes = 1, resets = 0, repeat = 2, ext_offset = 105 2499 successes = 1, resets = 0, repeat = 2, ext_offset = 113 2451 2451 2451 2451 2451 successes = 5, resets = 0, repeat = 2, ext_offset = 115 1 1 successes = 2, resets = 0, repeat = 2, ext_offset = 128 1 successes = 1, resets = 0, repeat = 2, ext_offset = 135 2451 2501 2501 2501 successes = 4, resets = 0, repeat = 2, ext_offset = 146 2451 2501 2501 2501 2501 successes = 5, resets = 0, repeat = 2, ext_offset = 153 2501 2501 2501 2501 2501 successes = 5, resets = 0, repeat = 2, ext_offset = 154 2498 2451 2498 successes = 3, resets = 2, repeat = 2, ext_offset = 161 2451 2498 successes = 2, resets = 2, repeat = 2, ext_offset = 168 2451 2498 2451 successes = 3, resets = 2, repeat = 2, ext_offset = 169 2498 2498 2498 2498 successes = 4, resets = 0, repeat = 2, ext_offset = 172 2499 successes = 1, resets = 2, repeat = 2, ext_offset = 176 2499 successes = 1, resets = 2, repeat = 2, ext_offset = 183 2498 2498 2498 2498 2498 successes = 5, resets = 0, repeat = 2, ext_offset = 185 2351 2499 2351 successes = 3, resets = 1, repeat = 2, ext_offset = 187 2498 2498 2498 2498 2498 successes = 5, resets = 0, repeat = 2, ext_offset = 194 2484 successes = 1, resets = 1, repeat = 5, ext_offset = 9 2501 2501 2501 successes = 3, resets = 0, repeat = 5, ext_offset = 10 2501 2501 2451 2501 2451 successes = 5, resets = 0, repeat = 5, ext_offset = 17 2451 2497 2451 2501 2451 successes = 5, resets = 0, repeat = 5, ext_offset = 24 2497 2451 2501 2451 successes = 4, resets = 0, repeat = 5, ext_offset = 25 2451 2451 successes = 2, resets = 0, repeat = 5, ext_offset = 28 2451 2501 2501 2451 successes = 4, resets = 1, repeat = 5, ext_offset = 32 2451 2501 2451 2501 successes = 4, resets = 1, repeat = 5, ext_offset = 39 2501 2501 2501 2501 2501 successes = 5, resets = 0, repeat = 5, ext_offset = 43 2501 2501 2501 2501 2501 successes = 5, resets = 0, repeat = 5, ext_offset = 50 2501 2501 2501 2501 2501 successes = 5, resets = 0, repeat = 5, ext_offset = 57 2501 2501 2501 2501 2501 successes = 5, resets = 0, repeat = 5, ext_offset = 58 2451 2451 successes = 2, resets = 2, repeat = 5, ext_offset = 80 2451 2451 successes = 2, resets = 2, repeat = 5, ext_offset = 87 2451 successes = 1, resets = 1, repeat = 5, ext_offset = 90 2451 2451 2451 successes = 3, resets = 2, repeat = 5, ext_offset = 91 2499 2499 successes = 2, resets = 0, repeat = 5, ext_offset = 98 2451 2451 2451 2451 2451 successes = 5, resets = 0, repeat = 5, ext_offset = 104 2499 successes = 1, resets = 1, repeat = 5, ext_offset = 113 2451 2451 2451 2451 2451 successes = 5, resets = 0, repeat = 5, ext_offset = 115 1 1 successes = 2, resets = 0, repeat = 5, ext_offset = 128 2451 2501 2501 2501 successes = 4, resets = 0, repeat = 5, ext_offset = 146 2501 2501 2501 2501 2501 successes = 5, resets = 0, repeat = 5, ext_offset = 153 2501 2501 2501 2501 2501 successes = 5, resets = 0, repeat = 5, ext_offset = 154 2498 2451 successes = 2, resets = 3, repeat = 5, ext_offset = 161 2498 2451 successes = 2, resets = 3, repeat = 5, ext_offset = 168 2498 2498 2498 successes = 3, resets = 2, repeat = 5, ext_offset = 169 Done glitching
In [11]:
%matplotlib inline
gc.results.plot_2d(plotdots={"success":"+g", "reset":"xr", "normal":None})
Out [11]:
In [12]:
scope.dis()
target.dis()
Unlike the other ChipWhisperers, the Nano doesn’t have sychronous
glitching. This means that ext_offset is a mixture of both the
offset within the clock cycle, which affects glitch success, and
ext_offset, which affects which instruction is being glitched. As such,
ext_offset settings you find in this lab won’t be directly applicable to
other labs. That being said, good ranges for repeat and the success rate
of glitches still gives valuable information that you can apply to other
labs.
In [ ]:
