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Avoid branches in Montgomery Double() (GH #869)

pull/873/head
Jeffrey Walton 2019-08-06 01:23:37 -04:00
parent df18c5b745
commit 5ae70e22b9
No known key found for this signature in database
GPG Key ID: B36AB348921B1838
1 changed files with 39 additions and 34 deletions
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73
ecp.cpp
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@ -41,10 +41,9 @@ inline ECP::Point FromMontgomery(const ModularArithmetic &mr, const ECP::Point &
return P.identity ? P : ECP::Point(mr.ConvertOut(P.x), mr.ConvertOut(P.y));
}
template <typename T>
inline Integer ToInteger(const T& val)
inline Integer IdentityToInteger(bool val)
{
return !!val ? Integer::One() : Integer::Zero();
return val ? Integer::One() : Integer::Zero();
}
ANONYMOUS_NAMESPACE_END
@ -531,9 +530,9 @@ ECP::Point ECP::AdditionFunction::operator()(const Point& P) const
// Gyrations attempt to maintain constant-timeness
// We need either (P.x, P.y, 1) or (0, 1, 0).
const Integer x = P.x * ToInteger(!P.identity);
const Integer y = P.y * ToInteger(!P.identity) + 1 * ToInteger(P.identity);
const Integer z = 1 * ToInteger(!P.identity);
const Integer x = P.x * IdentityToInteger(!P.identity);
const Integer y = P.y * IdentityToInteger(!P.identity) + 1 * IdentityToInteger(P.identity);
const Integer z = 1 * IdentityToInteger(!P.identity);
ProjectivePoint p(x, y, z), r;
@ -587,9 +586,9 @@ ECP::Point ECP::AdditionFunction::operator()(const Point& P) const
// Gyrations attempt to maintain constant-timeness
// We need either (P.x, P.y, 1) or (0, 1, 0).
const Integer x = P.x * ToInteger(!P.identity);
const Integer y = P.y * ToInteger(!P.identity) + 1 * ToInteger(P.identity);
const Integer z = 1 * ToInteger(!P.identity);
const Integer x = P.x * IdentityToInteger(!P.identity);
const Integer y = P.y * IdentityToInteger(!P.identity) + 1 * IdentityToInteger(P.identity);
const Integer z = 1 * IdentityToInteger(!P.identity);
ProjectivePoint p(x, y, z), r;
@ -627,9 +626,9 @@ ECP::Point ECP::AdditionFunction::operator()(const Point& P) const
// Gyrations attempt to maintain constant-timeness
// We need either (P.x, P.y, 1) or (0, 1, 0).
const Integer x = P.x * ToInteger(!P.identity);
const Integer y = P.y * ToInteger(!P.identity) + 1 * ToInteger(P.identity);
const Integer z = 1 * ToInteger(!P.identity);
const Integer x = P.x * IdentityToInteger(!P.identity);
const Integer y = P.y * IdentityToInteger(!P.identity) + 1 * IdentityToInteger(P.identity);
const Integer z = 1 * IdentityToInteger(!P.identity);
ProjectivePoint p(x, y, z), r;
@ -664,17 +663,23 @@ ECP::Point ECP::AdditionFunction::operator()(const Point& P) const
{
ECP::Point& m_R = m_ecp.m_R;
const ECP::Field& field = m_ecp.GetField();
const FieldElement& a = m_ecp.m_a;
if (P.identity || P.y==field.Identity()) return m_ecp.Identity();
// More gyrations
bool identity = P.identity | P.y==field.Identity();
FieldElement t = field.Square(P.x);
t = field.Add(field.Add(field.Double(t), t), m_ecp.m_a);
t = field.Add(field.Add(field.Double(t), t), a);
t = field.Divide(t, field.Double(P.y));
FieldElement x = field.Subtract(field.Subtract(field.Square(t), P.x), P.x);
m_R.y = field.Subtract(field.Multiply(t, field.Subtract(P.x, x)), P.y);
m_R.x.swap(x);
m_R.identity = false;
// More gyrations
m_R.x *= IdentityToInteger(!identity);
m_R.y *= IdentityToInteger(!identity);
m_R.identity = identity;
return m_R;
}
}
@ -688,13 +693,13 @@ ECP::Point ECP::AdditionFunction::operator()(const Point& P, const Point& Q) con
// Gyrations attempt to maintain constant-timeness
// We need either (P.x, P.y, 1) or (0, 1, 0).
const Integer x1 = P.x * ToInteger(!P.identity);
const Integer y1 = P.y * ToInteger(!P.identity) + 1 * ToInteger(P.identity);
const Integer z1 = 1 * ToInteger(!P.identity);
const Integer x1 = P.x * IdentityToInteger(!P.identity);
const Integer y1 = P.y * IdentityToInteger(!P.identity) + 1 * IdentityToInteger(P.identity);
const Integer z1 = 1 * IdentityToInteger(!P.identity);
const Integer x2 = Q.x * ToInteger(!Q.identity);
const Integer y2 = Q.y * ToInteger(!Q.identity) + 1 * ToInteger(Q.identity);
const Integer z2 = 1 * ToInteger(!Q.identity);
const Integer x2 = Q.x * IdentityToInteger(!Q.identity);
const Integer y2 = Q.y * IdentityToInteger(!Q.identity) + 1 * IdentityToInteger(Q.identity);
const Integer z2 = 1 * IdentityToInteger(!Q.identity);
ProjectivePoint p(x1, y1, z1), q(x2, y2, z2), r;
@ -757,13 +762,13 @@ ECP::Point ECP::AdditionFunction::operator()(const Point& P, const Point& Q) con
// Gyrations attempt to maintain constant-timeness
// We need either (P.x, P.y, 1) or (0, 1, 0).
const Integer x1 = P.x * ToInteger(!P.identity);
const Integer y1 = P.y * ToInteger(!P.identity) + 1 * ToInteger(P.identity);
const Integer z1 = 1 * ToInteger(!P.identity);
const Integer x1 = P.x * IdentityToInteger(!P.identity);
const Integer y1 = P.y * IdentityToInteger(!P.identity) + 1 * IdentityToInteger(P.identity);
const Integer z1 = 1 * IdentityToInteger(!P.identity);
const Integer x2 = Q.x * ToInteger(!Q.identity);
const Integer y2 = Q.y * ToInteger(!Q.identity) + 1 * ToInteger(Q.identity);
const Integer z2 = 1 * ToInteger(!Q.identity);
const Integer x2 = Q.x * IdentityToInteger(!Q.identity);
const Integer y2 = Q.y * IdentityToInteger(!Q.identity) + 1 * IdentityToInteger(Q.identity);
const Integer z2 = 1 * IdentityToInteger(!Q.identity);
ProjectivePoint p(x1, y1, z1), q(x2, y2, z2), r;
@ -802,13 +807,13 @@ ECP::Point ECP::AdditionFunction::operator()(const Point& P, const Point& Q) con
// Gyrations attempt to maintain constant-timeness
// We need either (P.x, P.y, 1) or (0, 1, 0).
const Integer x1 = P.x * ToInteger(!P.identity);
const Integer y1 = P.y * ToInteger(!P.identity) + 1 * ToInteger(P.identity);
const Integer z1 = 1 * ToInteger(!P.identity);
const Integer x1 = P.x * IdentityToInteger(!P.identity);
const Integer y1 = P.y * IdentityToInteger(!P.identity) + 1 * IdentityToInteger(P.identity);
const Integer z1 = 1 * IdentityToInteger(!P.identity);
const Integer x2 = Q.x * ToInteger(!Q.identity);
const Integer y2 = Q.y * ToInteger(!Q.identity) + 1 * ToInteger(Q.identity);
const Integer z2 = 1 * ToInteger(!Q.identity);
const Integer x2 = Q.x * IdentityToInteger(!Q.identity);
const Integer y2 = Q.y * IdentityToInteger(!Q.identity) + 1 * IdentityToInteger(Q.identity);
const Integer z2 = 1 * IdentityToInteger(!Q.identity);
ProjectivePoint p(x1, y1, z1), q(x2, y2, z2), r;