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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 typing import Iterator, List, Tuple, TypeVar, Any
from copy import deepcopy from copy import deepcopy
from itertools import chain from itertools import chain
from math import ceil
from . import test_case from . import test_case
from . import test_data_generation 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 all pair combinations from input values."""
return [(x, y) for x in values for y in 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: def hex_digits_for_limb(limbs: int, bits_in_limb: int) -> int:
""" Retrun the hex digits need for a number of limbs. """ """ Return the hex digits need for a number of limbs. """
return 2 * (limbs * bits_in_limb // 8) return 2 * ((limbs * bits_in_limb) // 8)
def hex_digits_max_int(val: str, bits_in_limb: int) -> int: def hex_digits_max_int(val: str, bits_in_limb: int) -> int:
""" Return the first number exceeding maximum the limb space """ 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 @property
def arg_a(self) -> str: 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) return super().format_arg('{:x}'.format(self.int_a)).zfill(hex_digits)
def result(self) -> List[str]: def result(self) -> List[str]:
@ -624,7 +625,8 @@ class EcpP224K1Raw(bignum_common.ModOperationCommon,
@property @property
def arg_a(self) -> str: 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) return super().format_arg('{:x}'.format(self.int_a)).zfill(hex_digits)
def result(self) -> List[str]: def result(self) -> List[str]: