/*
* Multiply the provided (encoded) point G by a scalar x. Scalar
* encoding is big-endian. The scalar value shall be non-zero and
* lower than the subgroup order (exception: some curves allow
* larger ranges).
*
* The result is written in the provided D[] array, using either
* compressed or uncompressed format (for some curves, output is
* always compressed). The array shall have the appropriate length.
* Returned value is -1 on success, 0 on error. If 0 is returned
* then the array contents are indeterminate.
*
* G and D need not be distinct arrays.
*/
public uint Mul(byte[] G, byte[] x, byte[] D, bool compressed)
{
MutableECPoint P = MakeZero();
uint good = P.DecodeCT(G);
good &= ~P.IsInfinityCT;
good &= P.MulSpecCT(x);
good &= P.Encode(D, compressed);
return(good);
}
/*
* Given points A and B, and scalar x and y, return x*A+y*B. This
* is used for ECDSA. Scalars use big-endian encoding and must be
* non-zero and lower than the subgroup order.
*
* The result is written in the provided D[] array, using either
* compressed or uncompressed format (for some curves, output is
* always compressed). The array shall have the appropriate length.
* Returned value is -1 on success, 0 on error. If 0 is returned
* then the array contents are indeterminate.
*
* Not all curves support this operation; if the curve does not,
* then an exception is thrown.
*
* A, B and D need not be distinct arrays.
*/
public uint MulAdd(byte[] A, byte[] x, byte[] B, byte[] y,
byte[] D, bool compressed)
{
MutableECPoint P = MakeZero();
MutableECPoint Q = MakeZero();
/*
* Decode both points.
*/
uint good = P.DecodeCT(A);
good &= Q.DecodeCT(B);
good &= ~P.IsInfinityCT & ~Q.IsInfinityCT;
/*
* Perform both point multiplications.
*/
good &= P.MulSpecCT(x);
good &= Q.MulSpecCT(y);
good &= ~P.IsInfinityCT & ~Q.IsInfinityCT;
/*
* Perform addition. The AddCT() function may fail if
* P = Q, in which case we must compute 2Q and use that
* value instead.
*/
uint z = P.AddCT(Q);
Q.DoubleCT();
P.Set(Q, ~z);
/*
* Encode the result. The Encode() function will report
* an error if the addition result is infinity.
*/
good &= P.Encode(D, compressed);
return(good);
}
