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Makes modular exponentiation constant time by default. #128

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Makes modular exponentiation constant time by default. #128

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7c42a01
Makes modular exponentiation constant time by default.
ddealmei Jan 27, 2021
d434bf6
Fix issue with even modulus (constant time is only supproted for odd …
ddealmei Jan 27, 2021
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6 changes: 6 additions & 0 deletions bignum.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -682,6 +682,9 @@ NAN_METHOD(BigNum::Bpowm)
BigNum *bn1 = Nan::ObjectWrap::Unwrap<BigNum>(info[0]->ToObject(info.GetIsolate()->GetCurrentContext()).ToLocalChecked());
BigNum *bn2 = Nan::ObjectWrap::Unwrap<BigNum>(info[1]->ToObject(info.GetIsolate()->GetCurrentContext()).ToLocalChecked());
BigNum *res = new BigNum();
// Constant-time flag only supported for odd modulus
if (BN_is_odd(bn2->bignum_))
BN_set_flags(bn1->bignum_, BN_FLG_CONSTTIME);
BN_mod_exp(res->bignum_, bignum->bignum_, bn1->bignum_, bn2->bignum_, ctx);

WRAP_RESULT(res, result);
Expand All @@ -699,6 +702,9 @@ NAN_METHOD(BigNum::Upowm)
BigNum *exp = new BigNum(x);

BigNum *res = new BigNum();
// Constant-time flag only supported for odd modulus
if (BN_is_odd(bn->bignum_))
BN_set_flags(exp->bignum_, BN_FLG_CONSTTIME);
BN_mod_exp(res->bignum_, bignum->bignum_, exp->bignum_, bn->bignum_, ctx);

WRAP_RESULT(res, result);
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