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g^x mod p using precalculated table

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orignal 2016-04-09 22:44:13 -04:00
parent c45aab7cef
commit ffc666eaaa
1 changed files with 39 additions and 9 deletions
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48
Crypto.cpp
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@ -153,32 +153,62 @@ namespace crypto
#define elgp GetCryptoConstants ().elgp #define elgp GetCryptoConstants ().elgp
#define elgg GetCryptoConstants ().elgg #define elgg GetCryptoConstants ().elgg
void PrecalculateElggTable (BIGNUM * table[][256], int len) // table is len's array of array of 256 bignums void PrecalculateElggTable (BIGNUM * table[][255], int len) // table is len's array of array of 255 bignums
{ {
if (len <= 0) return; if (len <= 0) return;
BN_CTX * ctx = BN_CTX_new (); BN_CTX * ctx = BN_CTX_new ();
BN_MONT_CTX * montCtx = BN_MONT_CTX_new (); BN_MONT_CTX * montCtx = BN_MONT_CTX_new ();
BN_MONT_CTX_set (montCtx, elgp, ctx); BN_MONT_CTX_set (montCtx, elgp, ctx);
BIGNUM * elggMont = BN_new ();
BN_from_montgomery(elggMont, elgg, montCtx, ctx);
for (int i = 0; i < len; i++) for (int i = 0; i < len; i++)
{ {
table[i][0] = BN_new (); table[i][0] = BN_new ();
if (!i) if (!i)
BN_from_montgomery (table[0][0], BN_value_one (), montCtx, ctx); // 2^0 = 1 BN_to_montgomery (table[0][0], elgg, montCtx, ctx);
else else
BN_mod_mul_montgomery (table[i][0], table[i-1][255], elggMont, montCtx, ctx); BN_mod_mul_montgomery (table[i][0], table[i-1][254], table[i-1][0], montCtx, ctx);
for (int j = 1; j < 256; j++) for (int j = 1; j < 255; j++)
{ {
table[i][j] = BN_new (); table[i][j] = BN_new ();
BN_mod_mul_montgomery (table[i][j], table[i][j-1], elggMont, montCtx, ctx); BN_mod_mul_montgomery (table[i][j], table[i][j-1], table[i][0], montCtx, ctx);
} }
} }
BN_free (elggMont);
BN_MONT_CTX_free (montCtx); BN_MONT_CTX_free (montCtx);
BN_CTX_free (ctx); BN_CTX_free (ctx);
} }
BIGNUM * ElggPow (const uint8_t * exp, int len, BIGNUM * table[][255], BN_CTX * ctx)
// exp is in Big Endian
{
if (len <= 0) return nullptr;
BIGNUM * res = nullptr;
BN_MONT_CTX * montCtx = BN_MONT_CTX_new ();
BN_MONT_CTX_set (montCtx, elgp, ctx);
for (int i = 0; i < len; i++)
{
if (res)
{
if (exp[i])
BN_mod_mul_montgomery (res, res, table[len-1-i][exp[i]-1], montCtx, ctx);
}
else if (exp[i])
res = BN_dup (table[len-i-1][exp[i]-1]);
}
if (res)
BN_from_montgomery (res, res, montCtx, ctx);
BN_MONT_CTX_free (montCtx);
return res;
}
BIGNUM * ElggPow (const BIGNUM * exp, BIGNUM * table[][255], BN_CTX * ctx)
{
auto len = BN_num_bytes (exp);
uint8_t * buf = new uint8_t[len];
BN_bn2bin (exp, buf);
auto ret = ElggPow (buf, len, table, ctx);
delete[] buf;
return ret;
}
// DH // DH
DHKeys::DHKeys (): m_IsUpdated (true) DHKeys::DHKeys (): m_IsUpdated (true)