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/*
* NIST curve reduction
* (C) 2014 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/internal/curve_nistp.h>
#include <botan/internal/mp_core.h>
#include <botan/internal/rounding.h>
#include <botan/hex.h>
namespace Botan {
void CurveGFp_NIST::curve_mul(BigInt& z, const BigInt& x, const BigInt& y,
secure_vector<word>& ws) const
{
if(x.is_zero() || y.is_zero())
{
z = 0;
return;
}
const size_t p_words = get_p_words();
const size_t output_size = 2*p_words + 1;
ws.resize(2*(p_words+2));
z.grow_to(output_size);
z.clear();
bigint_mul(z.mutable_data(), output_size, &ws[0],
x.data(), x.size(), x.sig_words(),
y.data(), y.size(), y.sig_words());
this->redc(z, ws);
}
void CurveGFp_NIST::curve_sqr(BigInt& z, const BigInt& x,
secure_vector<word>& ws) const
{
if(x.is_zero())
{
z = 0;
return;
}
const size_t p_words = get_p_words();
const size_t output_size = 2*p_words + 1;
ws.resize(2*(p_words+2));
z.grow_to(output_size);
z.clear();
bigint_sqr(z.mutable_data(), output_size, &ws[0],
x.data(), x.size(), x.sig_words());
this->redc(z, ws);
}
//static
const BigInt& CurveGFp_P521::prime()
{
static const BigInt p521("0x1FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
"FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF");
return p521;
}
void CurveGFp_P521::redc(BigInt& x, secure_vector<word>& ws) const
{
const size_t p_words = get_p_words();
const size_t shift_words = 521 / MP_WORD_BITS,
shift_bits = 521 % MP_WORD_BITS;
const size_t x_sw = x.sig_words();
if(x_sw < p_words)
return; // already smaller
if(ws.size() < p_words + 1)
ws.resize(p_words + 1);
clear_mem(&ws[0], ws.size());
bigint_shr2(&ws[0], x.data(), x_sw, shift_words, shift_bits);
x.mask_bits(521);
bigint_add3(x.mutable_data(), x.data(), p_words, &ws[0], p_words);
normalize(x, ws, max_redc_subtractions());
}
}
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