/// <summary>バイト配列より点を作成する (SEC1, 2.3.4)</summary> public ECPoint(ECGroup group, byte[] data) { _group = group; _field = group.FiniteField; switch (data[0]) { case 0: { // 無限遠点 ECPoint tmp = _field.GetInfinityPoint(_group); _x = tmp._x; _y = tmp._y; _z = tmp._z; return; } case 2: case 3: { // 点圧縮済みデータ int keyBits = group.P.BitCount(); int keyBytes = (keyBits >> 3) + ((keyBits & 7) == 0 ? 0 : 1); if (data.Length != keyBytes + 1) { throw new ArgumentException(); } Number x = _field.ToElement(new Number(data, 1, keyBytes, false)); Number y2 = _field.Add(_field.Multiply(_field.Add(_field.Multiply(x, x), _group.A), x), _group.B); // (x^2 + a)*x + b Number y = _field.Sqrt(y2); if (_field.ToNormal(y).GetBit(0) != data[0] - 2) { y = _field.Modulus - y; } _x = x; _y = y; _z = _field.ToElement(Number.One); return; } case 4: { // 非圧縮データ int keyBits = group.P.BitCount(); int keyBytes = (keyBits >> 3) + ((keyBits & 7) == 0 ? 0 : 1); _x = _field.ToElement(new Number(data, 1, keyBytes, false)); _y = _field.ToElement(new Number(data, 1 + keyBytes, keyBytes, false)); _z = _field.ToElement(Number.One); return; } default: throw new ArgumentException(); } }
/// <summary>バイト配列より点を作成する (SEC1, 2.3.4)</summary> public ECPoint (ECGroup group, byte[] data) { _group = group; _field = group.FiniteField; switch (data[0]) { case 0: { // 無限遠点 ECPoint tmp = _field.GetInfinityPoint (_group); _x = tmp._x; _y = tmp._y; _z = tmp._z; return; } case 2: case 3: { // 点圧縮済みデータ int keyBits = group.P.BitCount (); int keyBytes = (keyBits >> 3) + ((keyBits & 7) == 0 ? 0 : 1); if (data.Length != keyBytes + 1) throw new ArgumentException (); Number x = _field.ToElement (new Number (data, 1, keyBytes, false)); Number y2 = _field.Add (_field.Multiply (_field.Add (_field.Multiply (x, x), _group.A), x), _group.B); // (x^2 + a)*x + b Number y = _field.Sqrt (y2); if (_field.ToNormal (y).GetBit (0) != data[0] - 2) y = _field.Modulus - y; _x = x; _y = y; _z = _field.ToElement (Number.One); return; } case 4: { // 非圧縮データ int keyBits = group.P.BitCount (); int keyBytes = (keyBits >> 3) + ((keyBits & 7) == 0 ? 0 : 1); _x = _field.ToElement (new Number (data, 1, keyBytes, false)); _y = _field.ToElement (new Number (data, 1 + keyBytes, keyBytes, false)); _z = _field.ToElement (Number.One); return; } default: throw new ArgumentException (); } }