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bignum_common.py: Added bits_to_limbs method.

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This patch introduces a rounding-error-resiliant method to
calculate bits_to_limbs, and is updating `SECP224R1` and
`SECP224K1` to use it.

Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
This commit is contained in:
Minos Galanakis 2023-06-27 16:34:59 +01:00
parent 23394b17bc
commit 80c4ae893c
2 changed files with 12 additions and 4 deletions
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10
scripts/mbedtls_dev/bignum_common.py
View File

@ -19,6 +19,7 @@ import enum
from typing import Iterator, List, Tuple, TypeVar, Any
from copy import deepcopy
from itertools import chain
from math import ceil
from . import test_case
from . import test_data_generation
@ -76,9 +77,14 @@ def combination_pairs(values: List[T]) -> List[Tuple[T, T]]:
"""Return all pair combinations from input values."""
return [(x, y) for x in values for y in values]
def bits_to_limbs(bits: int, bits_in_limb: int) -> int:
""" Return the appropriate ammount of limbs needed to store
a number contained in input bits"""
return ceil(bits / bits_in_limb)
def hex_digits_for_limb(limbs: int, bits_in_limb: int) -> int:
""" Retrun the hex digits need for a number of limbs. """
return 2 * (limbs * bits_in_limb // 8)
""" Return the hex digits need for a number of limbs. """
return 2 * ((limbs * bits_in_limb) // 8)
def hex_digits_max_int(val: str, bits_in_limb: int) -> int:
""" Return the first number exceeding maximum the limb space

6
scripts/mbedtls_dev/ecp.py
View File

@ -165,7 +165,8 @@ class EcpP224R1Raw(bignum_common.ModOperationCommon,
@property
def arg_a(self) -> str:
hex_digits = bignum_common.hex_digits_for_limb(448 // self.bits_in_limb, self.bits_in_limb)
limbs = 2 * bignum_common.bits_to_limbs(224, self.bits_in_limb)
hex_digits = bignum_common.hex_digits_for_limb(limbs, self.bits_in_limb)
return super().format_arg('{:x}'.format(self.int_a)).zfill(hex_digits)
def result(self) -> List[str]:
@ -624,7 +625,8 @@ class EcpP224K1Raw(bignum_common.ModOperationCommon,
@property
def arg_a(self) -> str:
hex_digits = bignum_common.hex_digits_for_limb(448 // self.bits_in_limb, self.bits_in_limb)
limbs = 2 * bignum_common.bits_to_limbs(224, self.bits_in_limb)
hex_digits = bignum_common.hex_digits_for_limb(limbs, self.bits_in_limb)
return super().format_arg('{:x}'.format(self.int_a)).zfill(hex_digits)
def result(self) -> List[str]: