3 files changed, 17 insertions, 5 deletions
diff --git a/crypto/src/math/ec/multiplier/FixedPointCombMultiplier.cs b/crypto/src/math/ec/multiplier/FixedPointCombMultiplier.cs
index a8ef5a77a..05bb4000b 100644
--- a/crypto/src/math/ec/multiplier/FixedPointCombMultiplier.cs
+++ b/crypto/src/math/ec/multiplier/FixedPointCombMultiplier.cs
@@ -48,7 +48,7 @@ namespace Org.BouncyCastle.Math.EC.Multiplier
R = R.TwicePlus(lookupTable[index]);
}
- return R;
+ return R.Add(info.Offset);
}
protected virtual int GetWidthForCombSize(int combSize)
diff --git a/crypto/src/math/ec/multiplier/FixedPointPreCompInfo.cs b/crypto/src/math/ec/multiplier/FixedPointPreCompInfo.cs
index 56a6326a1..11bdadc6f 100644
--- a/crypto/src/math/ec/multiplier/FixedPointPreCompInfo.cs
+++ b/crypto/src/math/ec/multiplier/FixedPointPreCompInfo.cs
@@ -6,11 +6,13 @@
public class FixedPointPreCompInfo
: PreCompInfo
{
+ protected ECPoint m_offset = null;
+
/**
* Array holding the precomputed <code>ECPoint</code>s used for a fixed
* point multiplication.
*/
- protected ECPoint[] m_preComp = null;
+ protected ECPoint[] m_preComp = null;
/**
* The width used for the precomputation. If a larger width precomputation
@@ -19,6 +21,12 @@
*/
protected int m_width = -1;
+ public virtual ECPoint Offset
+ {
+ get { return m_offset; }
+ set { this.m_offset = value; }
+ }
+
public virtual ECPoint[] PreComp
{
get { return m_preComp; }
diff --git a/crypto/src/math/ec/multiplier/FixedPointUtilities.cs b/crypto/src/math/ec/multiplier/FixedPointUtilities.cs
index d927d010b..8e129a8f3 100644
--- a/crypto/src/math/ec/multiplier/FixedPointUtilities.cs
+++ b/crypto/src/math/ec/multiplier/FixedPointUtilities.cs
@@ -35,17 +35,20 @@ namespace Org.BouncyCastle.Math.EC.Multiplier
int bits = GetCombSize(c);
int d = (bits + minWidth - 1) / minWidth;
- ECPoint[] pow2Table = new ECPoint[minWidth];
+ ECPoint[] pow2Table = new ECPoint[minWidth + 1];
pow2Table[0] = p;
for (int i = 1; i < minWidth; ++i)
{
pow2Table[i] = pow2Table[i - 1].TimesPow2(d);
}
-
+
+ // This will be the 'offset' value
+ pow2Table[minWidth] = pow2Table[0].Subtract(pow2Table[1]);
+
c.NormalizeAll(pow2Table);
lookupTable = new ECPoint[n];
- lookupTable[0] = c.Infinity;
+ lookupTable[0] = pow2Table[0];
for (int bit = minWidth - 1; bit >= 0; --bit)
{
@@ -60,6 +63,7 @@ namespace Org.BouncyCastle.Math.EC.Multiplier
c.NormalizeAll(lookupTable);
+ info.Offset = pow2Table[minWidth];
info.PreComp = lookupTable;
info.Width = minWidth;
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