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/*
* Blinding for public key operations
* (C) 1999-2010,2015 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/blinding.h>
#include <botan/numthry.h>
#if defined(BOTAN_HAS_SYSTEM_RNG)
#include <botan/system_rng.h>
#else
#include <botan/auto_rng.h>
#endif
namespace Botan {
Blinder::Blinder(const BigInt& modulus,
std::function<BigInt (const BigInt&)> fwd,
std::function<BigInt (const BigInt&)> inv) :
m_reducer{Modular_Reducer(modulus)}, m_rng{}, m_fwd_fn(fwd), m_inv_fn(inv), m_modulus_bits{modulus.bits()}, m_e{}, m_d{}, m_counter{}
{
#if defined(BOTAN_HAS_SYSTEM_RNG)
m_rng.reset(new System_RNG);
#else
m_rng.reset(new AutoSeeded_RNG);
#endif
const BigInt k = blinding_nonce();
m_e = m_fwd_fn(k);
m_d = m_inv_fn(k);
}
BigInt Blinder::blinding_nonce() const
{
return BigInt(*m_rng, m_modulus_bits - 1);
}
BigInt Blinder::blind(const BigInt& i) const
{
if(!m_reducer.initialized())
throw Exception("Blinder not initialized, cannot blind");
++m_counter;
if(BOTAN_BLINDING_REINIT_INTERVAL > 0 && (m_counter % BOTAN_BLINDING_REINIT_INTERVAL == 0))
{
const BigInt k = blinding_nonce();
m_e = m_fwd_fn(k);
m_d = m_inv_fn(k);
}
else
{
m_e = m_reducer.square(m_e);
m_d = m_reducer.square(m_d);
}
return m_reducer.multiply(i, m_e);
}
BigInt Blinder::unblind(const BigInt& i) const
{
if(!m_reducer.initialized())
throw Exception("Blinder not initialized, cannot unblind");
return m_reducer.multiply(i, m_d);
}
}
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