Assume CurveGFp inputs are at most p words long

Lets us avoid calling sig_words much of the time. Improves ECDSA 5-7%

1 files changed, 27 insertions, 13 deletions

diff --git a/src/lib/pubkey/ec_group/curve_gfp.cpp b/src/lib/pubkey/ec_group/curve_gfp.cpp
index d841437f3..b57b8d3ef 100644
--- a/src/lib/pubkey/ec_group/curve_gfp.cpp
+++ b/src/lib/pubkey/ec_group/curve_gfp.cpp
@@ -89,10 +89,18 @@ void CurveGFp_Montgomery::to_curve_rep(BigInt& x, secure_vector<word>& ws) const
    curve_mul(x, tx, m_r2, ws);
    }
 
-void CurveGFp_Montgomery::from_curve_rep(BigInt& x, secure_vector<word>& ws) const
+void CurveGFp_Montgomery::from_curve_rep(BigInt& z, secure_vector<word>& ws) const
    {
-   const BigInt tx = x;
-   curve_mul(x, tx, 1, ws);
+   if(ws.size() < get_ws_size())
+      ws.resize(get_ws_size());
+
+   const size_t output_size = 2*m_p_words + 2;
+   if(z.size() < output_size)
+      z.grow_to(output_size);
+
+   bigint_monty_redc(z.mutable_data(),
+                     m_p.data(), m_p_words, m_p_dash,
+                     ws.data(), ws.size());
    }
 
 void CurveGFp_Montgomery::curve_mul(BigInt& z, const BigInt& x, const BigInt& y,
@@ -111,9 +119,12 @@ void CurveGFp_Montgomery::curve_mul(BigInt& z, const BigInt& x, const BigInt& y,
    if(z.size() < output_size)
       z.grow_to(output_size);
 
+   const size_t x_words = (x.size() >= m_p_words) ? m_p_words : x.sig_words();
+   const size_t y_words = (y.size() >= m_p_words) ? m_p_words : y.sig_words();
+
    bigint_mul(z.mutable_data(), z.size(),
-              x.data(), x.size(), x.sig_words(),
-              y.data(), y.size(), y.sig_words(),
+              x.data(), x.size(), x_words,
+              y.data(), y.size(), y_words,
               ws.data(), ws.size());
 
    bigint_monty_redc(z.mutable_data(),
@@ -130,19 +141,17 @@ void CurveGFp_Montgomery::curve_sqr(BigInt& z, const BigInt& x,
       return;
       }
 
-   const size_t x_sw = x.sig_words();
-   BOTAN_ASSERT(x_sw <= m_p_words, "Input in range");
-
    if(ws.size() < get_ws_size())
       ws.resize(get_ws_size());
 
    const size_t output_size = 2*m_p_words + 2;
-
    if(z.size() < output_size)
       z.grow_to(output_size);
 
+   const size_t x_words = (x.size() >= m_p_words) ? m_p_words : x.sig_words();
+
    bigint_sqr(z.mutable_data(), z.size(),
-              x.data(), x.size(), x_sw,
+              x.data(), x.size(), x_words,
               ws.data(), ws.size());
 
    bigint_monty_redc(z.mutable_data(),
@@ -216,9 +225,12 @@ void CurveGFp_NIST::curve_mul(BigInt& z, const BigInt& x, const BigInt& y,
    if(z.size() < output_size)
       z.grow_to(output_size);
 
+   const size_t x_words = (x.size() >= m_p_words) ? m_p_words : x.sig_words();
+   const size_t y_words = (y.size() >= m_p_words) ? m_p_words : y.sig_words();
+
    bigint_mul(z.mutable_data(), z.size(),
-              x.data(), x.size(), x.sig_words(),
-              y.data(), y.size(), y.sig_words(),
+              x.data(), x.size(), x_words,
+              y.data(), y.size(), y_words,
               ws.data(), ws.size());
 
    this->redc(z, ws);
@@ -240,8 +252,10 @@ void CurveGFp_NIST::curve_sqr(BigInt& z, const BigInt& x,
    if(z.size() < output_size)
       z.grow_to(output_size);
 
+   const size_t x_words = (x.size() >= m_p_words) ? m_p_words : x.sig_words();
+
    bigint_sqr(z.mutable_data(), output_size,
-              x.data(), x.size(), x.sig_words(),
+              x.data(), x.size(), x_words,
               ws.data(), ws.size());
 
    this->redc(z, ws);