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LibCrypto: Update ModularInverse implementation to use extended GCD

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The previous implementation of `ModularInverse` was flaky and did not
compute the correct value in many occasions, especially with big numbers
like in RSA.

Also added a bunch of tests with big numbers.
This commit is contained in:
devgianlu 2024-12-15 16:06:14 +01:00 • committed by Ali Mohammad Pur
commit f49a55d089
Notes: github-actions[bot] 2024-12-15 22:32:53 +00:00
4 changed files with 65 additions and 80 deletions
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23
Libraries/LibCrypto/NumberTheory/ModularFunctions.cpp
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@ -19,21 +19,26 @@ UnsignedBigInteger Mod(UnsignedBigInteger const& a, UnsignedBigInteger const& b)
return result;
}
UnsignedBigInteger ModularInverse(UnsignedBigInteger const& a_, UnsignedBigInteger const& b)
UnsignedBigInteger ModularInverse(UnsignedBigInteger const& a, UnsignedBigInteger const& b)
{
if (b == 1)
return { 1 };
UnsignedBigInteger temp_1;
UnsignedBigInteger temp_minus;
UnsignedBigInteger temp_quotient;
UnsignedBigInteger temp_d;
UnsignedBigInteger temp_u;
UnsignedBigInteger temp_v;
UnsignedBigInteger temp_x;
UnsignedBigInteger result;
UnsignedBigInteger temp_y;
UnsignedBigInteger temp_gcd;
UnsignedBigInteger temp_quotient;
UnsignedBigInteger temp_1;
UnsignedBigInteger temp_2;
UnsignedBigInteger temp_shift_result;
UnsignedBigInteger temp_shift_plus;
UnsignedBigInteger temp_shift;
UnsignedBigInteger temp_r;
UnsignedBigInteger temp_s;
UnsignedBigInteger temp_t;
UnsignedBigIntegerAlgorithms::modular_inverse_without_allocation(a, b, result, temp_y, temp_gcd, temp_quotient, temp_1, temp_2, temp_shift_result, temp_shift_plus, temp_shift, temp_r, temp_s, temp_t);
UnsignedBigIntegerAlgorithms::modular_inverse_without_allocation(a_, b, temp_1, temp_minus, temp_quotient, temp_d, temp_u, temp_v, temp_x, result);
return result;
}