diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/lib/pubkey/ec_group/point_mul.cpp | 11 |
1 files changed, 7 insertions, 4 deletions
diff --git a/src/lib/pubkey/ec_group/point_mul.cpp b/src/lib/pubkey/ec_group/point_mul.cpp index 41d61d0e2..d4a0b6ee6 100644 --- a/src/lib/pubkey/ec_group/point_mul.cpp +++ b/src/lib/pubkey/ec_group/point_mul.cpp @@ -14,7 +14,10 @@ namespace Botan { namespace { -const size_t PointGFp_SCALAR_BLINDING_BITS = 80; +size_t blinding_size(const BigInt& group_order) + { + return (group_order.bits() + 1) / 2; + } } @@ -62,7 +65,7 @@ PointGFp_Base_Point_Precompute::PointGFp_Base_Point_Precompute(const PointGFp& b * the size of the prime modulus. In all cases they are at most 1 bit * longer. The +1 compensates for this. */ - const size_t T_bits = round_up(p_bits + PointGFp_SCALAR_BLINDING_BITS + 1, WINDOW_BITS) / WINDOW_BITS; + const size_t T_bits = round_up(p_bits + blinding_size(mod_order.get_modulus()) + 1, WINDOW_BITS) / WINDOW_BITS; std::vector<PointGFp> T(WINDOW_SIZE*T_bits); @@ -116,7 +119,7 @@ PointGFp PointGFp_Base_Point_Precompute::mul(const BigInt& k, if(rng.is_seeded()) { // Choose a small mask m and use k' = k + m*order (Coron's 1st countermeasure) - const BigInt mask(rng, PointGFp_SCALAR_BLINDING_BITS); + const BigInt mask(rng, blinding_size(group_order)); scalar += group_order * mask; } else @@ -271,7 +274,7 @@ PointGFp PointGFp_Var_Point_Precompute::mul(const BigInt& k, ws.resize(PointGFp::WORKSPACE_SIZE); // Choose a small mask m and use k' = k + m*order (Coron's 1st countermeasure) - const BigInt mask(rng, PointGFp_SCALAR_BLINDING_BITS, false); + const BigInt mask(rng, blinding_size(group_order), false); const BigInt scalar = k + group_order * mask; const size_t elem_size = 3*m_p_words; |