/// <summary>
/// Computes the bits required for a given encoding of an elliptic curve point.
/// </summary>
/// <returns>The integer bit length of the encoded points.</returns>
/// <param name="encoding">The point encoding.</param>
/// <param name="elementBitLength">The bit length elements in the underlying field of the curve.</param>
public static int GetEncodingBitLength(PointEncoding encoding, int elementBitLength)
{
switch (encoding)
{
case PointEncoding.Compressed:
return(elementBitLength + 8);
default:
return(2 * elementBitLength + 8);
}
}
/// <summary>
/// Encodes the curve point in a byte buffer.
/// </summary>
/// <param name="encoding">The encoding scheme used to encode the point in the buffer.</param>
/// <returns>Byte buffer containing the encoded curve point.</returns>
public byte[] ToBytes(PointEncoding encoding = PointEncoding.Compressed)
{
using (var ctx = BigNumberContextHandle.Create())
{
int requiredBufferLength = ECPointHandle.ToByteBuffer(_ecGroup, Handle, encoding, null, ctx);
byte[] buffer = new byte[requiredBufferLength];
int writtenBytes = ECPointHandle.ToByteBuffer(_ecGroup, Handle, encoding, buffer, ctx);
Debug.Assert(writtenBytes == requiredBufferLength);
return(buffer);
}
}
public static int ToByteBuffer(ECGroupHandle group, ECPointHandle p, PointEncoding form, byte[]?buffer, BigNumberContextHandle ctx)
{
Debug.Assert(!group.IsInvalid, $"Accessed an invalid ECGroupHandle! <{nameof(group)}>");
Debug.Assert(!p.IsInvalid, $"Accessed an invalid ECPointHandle! <{nameof(p)}>");
Debug.Assert(!ctx.IsInvalid, $"Accessed an invalid BigNumberContextHandle! <{nameof(ctx)}>");
int bufferLen = 0;
if (buffer != null)
{
bufferLen = buffer.Length;
}
bufferLen = EC_POINT_point2oct(group, p, form, buffer, bufferLen, ctx);
if (bufferLen == 0)
{
throw new OpenSslNativeException();
}
return(bufferLen);
}
private extern static int EC_POINT_point2oct(ECGroupHandle group, ECPointHandle p, PointEncoding form, byte[]?buffer, int bufferLen, BigNumberContextHandle contextHandle);
