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Always set constant time operations for OpenSSL bignums 

set_consttime_flag was always True anyway
pull/263/head
Bogdan Opanchuk 2021-04-12 22:00:40 -07:00
parent fd9e1d44e5
commit 503a1c6a18
1 changed files with 7 additions and 16 deletions
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23
umbral/openssl.py
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@ -116,19 +116,16 @@ class Curve:
#
def _bn_new(set_consttime_flag=True):
def _bn_new():
"""
Returns a new and initialized OpenSSL BIGNUM.
The set_consttime_flag is set to True by default. When this instance of a
CurveBN object has BN_FLG_CONSTTIME set, OpenSSL will use constant time
operations whenever this CurveBN is passed.
"""
new_bn = backend._lib.BN_new()
backend.openssl_assert(new_bn != backend._ffi.NULL)
new_bn = backend._ffi.gc(new_bn, backend._lib.BN_clear_free)
if set_consttime_flag:
backend._lib.BN_set_flags(new_bn, backend._lib.BN_FLG_CONSTTIME)
# Always use constant time operations.
backend._lib.BN_set_flags(new_bn, backend._lib.BN_FLG_CONSTTIME)
return new_bn
@ -144,13 +141,10 @@ def bn_is_normalized(check_bn, modulus):
return (check_sign == 1 or check_sign == 0) and range_check == -1
def bn_from_int(py_int: int, check_modulus=None, set_consttime_flag=True):
def bn_from_int(py_int: int, check_modulus=None):
"""
Converts the given Python int to an OpenSSL BIGNUM. If ``modulus`` is
provided, it will check if the Python integer is within ``[0, modulus)``.
If set_consttime_flag is set to True, OpenSSL will use constant time
operations when using this CurveBN.
"""
conv_bn = backend._int_to_bn(py_int)
conv_bn = backend._ffi.gc(conv_bn, backend._lib.BN_clear_free)
@ -158,18 +152,15 @@ def bn_from_int(py_int: int, check_modulus=None, set_consttime_flag=True):
if check_modulus and not bn_is_normalized(conv_bn, check_modulus):
raise ValueError(f"The Python integer given ({py_int}) is not under the provided modulus.")
if set_consttime_flag:
backend._lib.BN_set_flags(conv_bn, backend._lib.BN_FLG_CONSTTIME)
backend._lib.BN_set_flags(conv_bn, backend._lib.BN_FLG_CONSTTIME)
return conv_bn
def bn_from_bytes(bytes_seq: bytes, set_consttime_flag=True, check_modulus=None, apply_modulus=None):
def bn_from_bytes(bytes_seq: bytes, check_modulus=None, apply_modulus=None):
"""
Converts the given byte sequence to an OpenSSL BIGNUM.
If set_consttime_flag is set to True, OpenSSL will use constant time
operations when using this BIGNUM.
"""
bn = _bn_new(set_consttime_flag)
bn = _bn_new()
backend._lib.BN_bin2bn(bytes_seq, len(bytes_seq), bn)
backend.openssl_assert(bn != backend._ffi.NULL)