blinding.cpp

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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/internal/blinding.h>
 
namespace Botan {
 
Blinder::Blinder(const BigInt& modulus,
                 RandomNumberGenerator& rng,
                 std::function<BigInt(const BigInt&)> fwd,
                 std::function<BigInt(const BigInt&)> inv) :
      m_reducer(modulus),
      m_rng(rng),
      m_fwd_fn(std::move(fwd)),
      m_inv_fn(std::move(inv)),
      m_modulus_bits(modulus.bits()),
      m_e{},
      m_d{},
      m_counter{} {
   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 Invalid_State("Blinder not initialized, cannot blind");
   }
 
   ++m_counter;
 
   if((BOTAN_BLINDING_REINIT_INTERVAL > 0) && (m_counter > BOTAN_BLINDING_REINIT_INTERVAL)) {
      const BigInt k = blinding_nonce();
      m_e = m_fwd_fn(k);
      m_d = m_inv_fn(k);
      m_counter = 0;
   } 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 Invalid_State("Blinder not initialized, cannot unblind");
   }
 
   return m_reducer.multiply(i, m_d);
}
 
}  // namespace Botan