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LibCrypto: Add optimized RSA decryption with CRT method

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The textbook RSA decryption method of `c^d % n` is quite slow. If the
necessary parameters are present, the CRT variant will be used.
Performing RSA decryption this way is ~3 times faster.
This commit is contained in:
devgianlu 2024-12-15 16:16:17 +01:00 • committed by Ali Mohammad Pur
parent ec990d620f
commit 57cc248883
Notes: github-actions[bot] 2024-12-15 22:32:40 +00:00
1 changed files with 16 additions and 4 deletions
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20
Libraries/LibCrypto/PK/RSA.cpp
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@ -133,12 +133,24 @@ void RSA::encrypt(ReadonlyBytes in, Bytes& out)
void RSA::decrypt(ReadonlyBytes in, Bytes& out)
{
// FIXME: Actually use the private key properly
auto in_integer = UnsignedBigInteger::import_data(in.data(), in.size());
auto exp = NumberTheory::ModularPower(in_integer, m_private_key.private_exponent(), m_private_key.modulus());
auto size = exp.export_data(out);
UnsignedBigInteger m;
if (m_private_key.prime1().is_zero() || m_private_key.prime2().is_zero()) {
m = NumberTheory::ModularPower(in_integer, m_private_key.private_exponent(), m_private_key.modulus());
} else {
auto m1 = NumberTheory::ModularPower(in_integer, m_private_key.exponent1(), m_private_key.prime1());
auto m2 = NumberTheory::ModularPower(in_integer, m_private_key.exponent2(), m_private_key.prime2());
if (m1 < m2)
m1 = m1.plus(m_private_key.prime1());
VERIFY(m1 >= m2);
auto h = NumberTheory::Mod(m1.minus(m2).multiplied_by(m_private_key.coefficient()), m_private_key.prime1());
m = m2.plus(h.multiplied_by(m_private_key.prime2()));
}
auto size = m.export_data(out);
auto align = m_private_key.length();
auto aligned_size = (size + align - 1) / align * align;