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gen_digital_signature_tests.py
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gen_digital_signature_tests.py
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#!/usr/bin/env python3
# SPDX-FileCopyrightText: 2021-2022 Espressif Systems (Shanghai) CO LTD
# SPDX-License-Identifier: Apache-2.0
import argparse
import datetime
import hashlib
import hmac
import os
import random
import struct
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives.asymmetric import rsa
from cryptography.hazmat.primitives.asymmetric.rsa import _modinv as modinv # type: ignore
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.utils import int_to_bytes
supported_targets = {'esp32s2', 'esp32c3', 'esp32s3', 'esp32c6'}
supported_key_size = {'esp32s2':[4096, 3072, 2048, 1024],
'esp32c3':[3072, 2048, 1024],
'esp32s3':[4096, 3072, 2048, 1024],
'esp32c6':[3072, 2048, 1024]}
NUM_HMAC_KEYS = 3
NUM_MESSAGES = 10
NUM_CASES = 6
def number_as_bignum_words(number): # type: (int) -> str
"""
Given a number, format result as a C array of words
(little-endian, same as ESP32 RSA peripheral or mbedTLS)
"""
result = []
while number != 0:
result.append('0x%08x' % (number & 0xFFFFFFFF))
number >>= 32
return '{ ' + ', '.join(result) + ' }'
def number_as_bytes(number, pad_bits=None): # type: (int, int) -> bytes
"""
Given a number, format as a little endian array of bytes
"""
result = int_to_bytes(number)[::-1] # type: bytes
while pad_bits is not None and len(result) < (pad_bits // 8):
result += b'\x00'
return result
def bytes_as_char_array(b): # type: (bytes) -> str
"""
Given a sequence of bytes, format as a char array
"""
return '{ ' + ', '.join('0x%02x' % x for x in b) + ' }'
def generate_tests_cases(target): # type: (str) -> None
max_key_size = max(supported_key_size[target])
print('Generating tests cases for {} (max key size = {})'.format(target, max_key_size))
hmac_keys = [os.urandom(32) for x in range(NUM_HMAC_KEYS)]
messages = [random.randrange(0, 1 << max_key_size) for x in range(NUM_MESSAGES)]
with open('digital_signature_test_cases.h', 'w') as f:
f.write('/*\n')
year = datetime.datetime.now().year
f.write(' * SPDX-FileCopyrightText: {year} Espressif Systems (Shanghai) CO LTD\n'.format(year=year))
f.write(' *\n')
f.write(' * SPDX-License-Identifier: Apache-2.0\n')
f.write(' *\n')
f.write(' * File generated by gen_digital_signature_tests.py\n')
f.write(' */\n')
# Write out HMAC keys
f.write('#define NUM_HMAC_KEYS %d\n\n' % NUM_HMAC_KEYS)
f.write('static const uint8_t test_hmac_keys[NUM_HMAC_KEYS][32] = {\n')
for h in hmac_keys:
f.write(' %s,\n' % bytes_as_char_array(h))
f.write('};\n\n')
# Write out messages
f.write('#define NUM_MESSAGES %d\n\n' % NUM_MESSAGES)
f.write('static const uint32_t test_messages[NUM_MESSAGES][%d/32] = {\n' % max_key_size)
for m in messages:
f.write(' // Message %d\n' % messages.index(m))
f.write(' %s,\n' % number_as_bignum_words(m))
f.write(' };\n')
f.write('\n\n\n')
f.write('#define NUM_CASES %d\n\n' % NUM_CASES)
f.write('static const encrypt_testcase_t test_cases[NUM_CASES] = {\n')
for case in range(NUM_CASES):
f.write(' { /* Case %d */\n' % case)
iv = os.urandom(16)
f.write(' .iv = %s,\n' % (bytes_as_char_array(iv)))
hmac_key_idx = random.randrange(0, NUM_HMAC_KEYS)
aes_key = hmac.HMAC(hmac_keys[hmac_key_idx], b'\xFF' * 32, hashlib.sha256).digest()
sizes = supported_key_size[target]
key_size = sizes[case % len(sizes)]
private_key = rsa.generate_private_key(
public_exponent=65537,
key_size=key_size,
backend=default_backend())
priv_numbers = private_key.private_numbers()
pub_numbers = private_key.public_key().public_numbers()
Y = priv_numbers.d
M = pub_numbers.n
rr = 1 << (key_size * 2)
rinv = rr % pub_numbers.n
mprime = - modinv(M, 1 << 32)
mprime &= 0xFFFFFFFF
length = key_size // 32 - 1
f.write(' .p_data = {\n')
f.write(' .Y = %s,\n' % number_as_bignum_words(Y))
f.write(' .M = %s,\n' % number_as_bignum_words(M))
f.write(' .Rb = %s,\n' % number_as_bignum_words(rinv))
f.write(' .M_prime = 0x%08x,\n' % mprime)
f.write(' .length = %d, // %d bit\n' % (length, key_size))
f.write(' },\n')
# calculate MD from preceding values and IV
# Y_max_key_size || M_max_key_size || Rb_max_key_size || M_prime32 || LENGTH32 || IV128
md_in = number_as_bytes(Y, max_key_size) + \
number_as_bytes(M, max_key_size) + \
number_as_bytes(rinv, max_key_size) + \
struct.pack('<II', mprime, length) + \
iv
md = hashlib.sha256(md_in).digest()
# generate expected C value from P bitstring
#
# Y_max_key_size || M_max_key_size || Rb_max_key_size || M_prime32 || LENGTH32 || 0x08*8
# E.g. for C3: Y3072 || M3072 || Rb3072 || M_prime32 || LENGTH32 || MD256 || 0x08*8
p = number_as_bytes(Y, max_key_size) + \
number_as_bytes(M, max_key_size) + \
number_as_bytes(rinv, max_key_size) + \
md + \
struct.pack('<II', mprime, length) + \
b'\x08' * 8
# expected_len = max_len_Y + max_len_M + max_len_rinv + md (32 bytes) + (mprime + length packed (8bytes)) + padding (8 bytes)
expected_len = (max_key_size / 8) * 3 + 32 + 8 + 8
assert len(p) == expected_len
cipher = Cipher(algorithms.AES(aes_key), modes.CBC(iv), backend=default_backend())
encryptor = cipher.encryptor()
c = encryptor.update(p) + encryptor.finalize()
f.write(' .expected_c = %s,\n' % bytes_as_char_array(c))
f.write(' .hmac_key_idx = %d,\n' % (hmac_key_idx))
f.write(' // results of message array encrypted with these keys\n')
f.write(' .expected_results = {\n')
mask = (1 << key_size) - 1 # truncate messages if needed
for m in messages:
f.write(' // Message %d\n' % messages.index(m))
f.write(' %s,' % (number_as_bignum_words(pow(m & mask, Y, M))))
f.write(' },\n')
f.write(' },\n')
f.write('};\n')
if __name__ == '__main__':
parser = argparse.ArgumentParser(description='''Generates Digital Signature Test Cases''')
parser.add_argument(
'--target',
required=True,
choices=supported_targets,
help='Target to generate test cases for, different targets support different max key length')
args = parser.parse_args()
generate_tests_cases(args.target)