Analyzer¶

You may want to use your captured traces to perform an attack based on a type of side-channel analysis, in comes the analyzer. You can import the analyzer API using:

import chipwhisperer.analyzer as cwa

One of the ways to analyze your traces is using correlation power analysis (CPA). The cpa function returns a CPA object that can be used to run the attack.

analyzer.cpa cpa(proj, leak_model, algorithm=cpa_algorithms.Progressive)¶

leakage_models¶

Contains all available leakage models that can be passed to the cpa function as the leak_model parameter.

Instance of the EightBitAES128LeakageModels class.

New in version 5.1: Add leakage_models to anlayzer API.

Preprocessing¶

Before performing an attack you may want to apply some pre-processing to the captured traces. There is currently one pre-processing class that has been moved to the latest ChipWhisperer API.

class ResyncSAD(trace_source=None)¶

Resynchronize traces by shifting them to match in a certain window.

This method of pre-processing uses the Sum of Absolute Difference (SAD) algorithm, also known as the Sum of Absolute Error. Uses a portion of one of the traces as a reference. This reference is then slid over the input “window” of each trace, and the amount of the shift resulting in the minimum SAD criteria is used as the shift amount for each trace.

Parameters: trace_source (Project) – A project containing the traces to preprocess.

property max_shift¶: Maximum amount to shift around a trace around the target_window

preprocess()¶

Process all traces.

Returns: A new project containing the processed traces.
Return type: Project

property ref_trace¶

The trace being used as a reference.

Raises: TypeError – If attempting to set to non integer value.

property target_window¶

Section of the trace we are trying to minimize SAD for.

This must be a tuple of (first point, last point).

Raises: TypeError – If attempting to set to a non tuple or if points are not integers.

Leakage Models¶

The analyzer includes various leakage models that can be passed to the cpa as the leak_model argument. The leakage_models variable provides a convenient way to list and access all the available leakage models:

import chipwhisperer.analyzer as cwa
print(cwa.leakage_models)

Any attribute can be chosen from this list and accessed with the dot syntax.

class EightBitAES128LeakageModels¶

Contains the available leakage models for 8 bit AES128.

To use a leakage model during a correlation power analysis attack see cpa.

leakage_models is an instance of this class.

__str__()¶

Structured glossary of all the different leakage models.

The glossary includes the name of the leakage model and the description (doc string).

property after_key_mix¶: Hamming weight of 1st round key mix (pt ^ key)

property inverse_sbox_output¶: Hamming weight of 1st round InvSBox (for decryption)

property inverse_sbox_output_alt¶: ISbox output with correct key scheduling so it’s highlighted in the jupyter callback

property last_round_state¶: Hamming weight of 9th round state (InvSBox output)

property last_round_state_diff¶: Hamming distance between rounds 9 and 10

property last_round_state_diff_alternate¶: Hamming distance between rounds 9 and 10 (alternate calculation)

property mix_columns_output¶: Hamming weight of 1st round mix columns

new_model(model)¶

Makes a new leakage model for use with analyzer

Usage:

class AES256_Round13_Model(cwa.AESLeakageHelper):
    def leakage(self, pt, ct, guess, bnum):
        # You must put YOUR recovered 14th round key here.
        # This example may not be accurate!
        calc_round_key = [0xea, 0x79, 0x79, 0x20, 0xc8, 0x71,
                          0x44, 0x7d, 0x46, 0x62, 0x5f, 0x51,
                          0x85, 0xc1, 0x3b, 0xcb]
        xored = [calc_round_key[i] ^ pt[i] for i in range(0, 16)]
        block = xored
        block = self.inv_shiftrows(block)
        block = self.inv_subbytes(block)
        block = self.inv_mixcolumns(block)
        block = self.inv_shiftrows(block)
        result = block
        return self.inv_sbox((result[bnum] ^ guess[bnum]))

leak_model = cwa.leakage_models.new_model(AES256_Round13_Model)

Parameters: model (AESLeakageHelper) – New leakage model to create
Returns: Leakage model made from model

property plaintext_key_xor¶: Hamming weight of 1st round key mix (pt ^ key)

property round_1_2_state_diff_key_mix¶: Hamming distance between initial key mix and round 1 key mix

property round_1_2_state_diff_sbox¶: Hamming distance between round 1 and round 2 sbox output

property round_1_2_state_diff_text¶: Hamming distance between AES input and mix columns output

property sbox_in_out_diff¶: Hamming distance between SBox input and output.

property sbox_input_successive¶: Hamming distance between 2 AES sbox inputs

property sbox_output¶: Hamming weight of 1st round SBox output

property sbox_output_successive¶: Hamming distance between 2 AES sbox outputs

property shift_rows_output¶: Hamming weight of shift rows output

property t_table¶: Hamming weight of t-table

property t_table_dec¶: Hamming weight of inverse t-table

CPA Attack¶

The interface class to carry out a correlation power analysis attack on the previously captured traces. The easiest way to create a default CPA instance that is ready to perform an attack is to use the cpa function.

class CPA(proj, leak_model, algorithm)¶

Correlation Power Analysis (CPA).

Provides all the needed functionality for taking a project and performing a CPA attack with a specific type of leakage model.

Parameters

proj (Project) – An open project instance.
algorithm – The algorithm used for the analysis. Default is Progressive which allows a callback to be given. The callback is called at increments of a specific interval. This is useful for auto-updating tables and equivalent.
leak_model – The leakage model used when analysing the captured traces.

The easiest way to use this class is through the cpa API function provided by the chipwhisperer.analyzer module.

Example:

import chipwhisperer.analyzer as cwa
import chipwhisperer as cw
proj = cw.open_project('/path/to/project')
attack = cwa.cpa(proj, cwa.leakage_models.sbox_output)
results = attack.run()
print(results)

project¶: Project to pull waves, textin, etc. from.

algorithm¶: Analysis algorithm to use for attack. Should be Progressive

leak_model¶: Leakage model to use during analysis. Should be of type AESLeakageHelper.

trace_range¶: Start and end trace number. Should be a list of length 2 (i.e. [start_num, end_num]).

point_range¶: Range of points to use from waves in project. Should be a list of length 2 ([start_point, end_point]).

subkey_list¶: List of subkeys to attack (subkey_list = [0, 1, 3] will attack subkeys 0, 1, and 3).

New in version 5.1: Added CPA in cpa_new.py to wrap old CPA object

change_project(proj)¶

Change the project property and update ranges

If you don’t want to update your ranges, change the project attribute instead.

Parameters: project (Project) – Project to switch to
Returns: None

run(callback=None, update_interval=25)¶

Runs the attack

Parameters

callback (function(), optional) – Callback to call every update interval. No arguments are passed to callback. Defaults to None.
update_interval (int, optional) – Number of traces to process before updating the results of the attack.

Returns

Results, the results of the attack. See documentation for Results for more details.

Results¶

The cpa.run function will return a results object. There are a few methods for interacting with the results object.

class Results(numSubkeys=16, numPerms=256)¶

Results type used for attacks generating peaks indicating the ‘best’ success. Examples include standard DPA & CPA attacks.

best_guesses()¶

Gets best subkey guesses from attack results

Returns: List of OrderedDicts with keys ‘guess’, ‘correlation’ and ‘pge’.

find_maximums(bytelist=None, use_absolute=True, use_single=False)¶

Information from the attack:

Parameters

bytelist (list) – Iterable of subkeys to compute and organize results for.
use_absolute (bool) – Use absolute value of correlation to find highest correlation.
use_single (bool) – All table values are taken from the same point the maximum is taken from.

Returns

Ordered by subkey index:

[subkey0_data, subkey1_data, subkey2_data, ...]

subkey0_data is another list containing guesses ordered by strength of correlation:

[guess0, guess1, guess2, ...]

guess0 is a tuple containing:

(key_guess, location_of_max, correlation)

Return type

list

For example, if you want to print the correlation of the best guess of the 4th subkey, you would run:

print(attack_results.find_maximums()[4][0][2])

Note the “point location of the max” is normally not calculated/tracked, and thus returns as a 0.

key_guess()¶

Get best guess for key in a list.

Returns: Guessed key as a list

set_known_key(known_key)¶: Sets the known encryption key.

simple_PGE(bnum)¶: Returns the partial guessing entropy of subkey.

Utilities¶

This section contains relatively independent functions that are useful for working with AES, and traces.

AES Functions¶

You may want to perform certain AES operations seperately. For this there is the AES helper functions. They are accessible using:

from chipwhisperer.analyzer import aes_funcs

Available functions:

aes_funcs.sbox
aes_funcs.inv_sbox
aes_funcs.subbytes
aes_funcs.inv_subbytes
aes_funcs.shiftrows
aes_funcs.inv_shiftrows
aes_funcs.mixcolumns
aes_funcs.inv_mixcolumns
aes_funcs.key_schedule_rounds

sbox(inp)¶

Perform an SBox lookup.

Parameters: inp (int) – Byte used for the Sbox lookup.
Returns: The result of the SBox lookup.
Return type: int

inv_sbox(inp)¶

Perform an inverse SBox lookup.

Parameters: inp (int) – Byte used for the inverse Sbox lookup.
Returns: The result of the inverse SBox lookup.
Return type: int

subbytes(inp)¶

Perform an Sbox lookup for multiple bytes.

Parameters

inp (iterable) – Bytes to perform Sbox lookup on.

Returns

List of bytes resulting from the multiple: SBox lookups.

Return type

list

inv_subbytes(inp)¶

Perform an inverse Sbox lookup for multiple bytes.

Parameters

inp (iterable) – Bytes to perform inverse Sbox lookup on.

Returns

List of bytes resulting from the multiple: inverse SBox lookups.

Return type

list

shiftrows(state)¶

AES shift rows operation.

Parameters: state (iterable) – Iterable of 16 bytes.
Returns: List of 16 bytes after shift rows operation.
Return type: list

inv_shiftrows(state)¶

Inverse AES shift rows operation.

Parameters: state (iterable) – Iterable of 16 bytes.
Returns: List of 16 bytes after inverse shift rows operation.
Return type: list

mixcolumns(state)¶

AES mix columns operation.

Parameters: state (iterable) – Iterable of 16 bytes.
Returns: List of 16 bytes after mix columns operation.
Return type: list

inv_mixcolumns(state)¶

AES inverse mix columns operation.

Parameters: state (iterable) – Iterable of 16 bytes.
Returns: List of 16 bytes after inverse mix columns operation.
Return type: list

key_schedule_rounds(input_key, input_round, desired_round)¶

Use key schedule to determine key for different round.

When dealing with AES-256, inputkey is 16 bytes and inputround indicates round that bytes 0…15 are from.

Parameters

input_key (list) – List of bytes of starting key, 16/32 bytes
input_round (int) – Starting round number (i.e. 0 = first)
desired_round (int) – Desired round number (i.e. 10 = last for 16-byte)

Returns

Key at desired round number. Can go forward or backwards.

Return type

list

Signal to Noise Ratio¶

Calculate the signal-to-noise ratio of your captured traces:

import chipwhisperer.analyzer as cwa
import chipwhisperer as cw

project = cw.open_project('my_project')
cwa.calculate_snr(project, cwa.leakage_models.sbox_output)

calculate_snr(input, leak_model, bnum=0, db=True)¶

Calculate the SNR based on the leakage model.

Uses same leakage model as the CPA attack.

Parameters

input (Iterable of Traces) – An iterable of traces.
leak_model (ModelsBase) – A leakage model selected from leakage_models.
bnum (int) – Byte number used for leakage model.
bd (bool) – Return signal-to-noise ratio in decibals.