/// <summary>
/// Verifies a signature of <paramref name="Data"/> made by the EdDSA algorithm.
/// </summary>
/// <param name="Data">Payload to sign.</param>
/// <param name="PublicKey">Public Key of the entity that generated the signature.</param>
/// <param name="HashFunction">Hash function to use.</param>
/// <param name="Curve">Elliptic curve</param>
/// <param name="Signature">Signature</param>
/// <returns>If the signature is valid.</returns>
public static bool Verify(byte[] Data, byte[] PublicKey, HashFunction HashFunction,
EdwardsCurveBase Curve, byte[] Signature)
{
try
{
int ScalarBytes = Signature.Length;
if ((ScalarBytes & 1) != 0)
{
return(false);
}
ScalarBytes >>= 1;
byte[] R = new byte[ScalarBytes];
Array.Copy(Signature, 0, R, 0, ScalarBytes);
PointOnCurve r = Decode(R, Curve);
byte[] S = new byte[ScalarBytes];
Array.Copy(Signature, ScalarBytes, S, 0, ScalarBytes);
BigInteger s = EllipticCurve.ToInt(S);
if (s >= Curve.Order)
{
return(false);
}
int c = Data.Length;
byte[] Bin = new byte[(ScalarBytes << 1) + c]; // dom2(F, C) = blank string
Array.Copy(R, 0, Bin, 0, ScalarBytes);
Array.Copy(PublicKey, 0, Bin, ScalarBytes, ScalarBytes);
Array.Copy(Data, 0, Bin, ScalarBytes << 1, c); // PH(M)=M
byte[] h = HashFunction(Bin);
BigInteger k = BigInteger.Remainder(EllipticCurve.ToInt(h), Curve.Order);
PointOnCurve P1 = Curve.ScalarMultiplication(s, Curve.BasePoint, false);
PointOnCurve P2 = Curve.ScalarMultiplication(k, Curve.Decode(PublicKey), false);
Curve.AddTo(ref P2, r);
P1.Normalize(Curve);
P2.Normalize(Curve);
return(P1.Equals(P2));
}
catch (ArgumentException)
{
return(false);
}
}
/// <summary>
/// Gets a shared key using the Elliptic Curve Diffie-Hellman (ECDH) algorithm.
/// </summary>
/// <param name="LocalPrivateKey">Local private key.</param>
/// <param name="RemotePublicKey">Public key of the remote party.</param>
/// <param name="HashFunction">A Hash function is applied to the derived key to generate the shared secret.
/// The derived key, as a byte array of equal size as the order of the prime field, ordered by most significant byte first,
/// is passed on to the hash function before being returned as the shared key.</param>
/// <param name="Curve">Elliptic curve used.</param>
/// <returns>Shared secret.</returns>
public static byte[] GetSharedKey(byte[] LocalPrivateKey, byte[] RemotePublicKey,
HashFunction HashFunction, EllipticCurve Curve)
{
PointOnCurve PublicKey = Curve.Decode(RemotePublicKey);
PointOnCurve P = Curve.ScalarMultiplication(LocalPrivateKey, PublicKey, true);
byte[] B = P.X.ToByteArray();
if (B.Length != Curve.OrderBytes)
{
Array.Resize <byte>(ref B, Curve.OrderBytes);
}
Array.Reverse(B); // Most significant byte first.
return(HashFunction(B));
}
/// <summary>
/// Doubles a point on the curve.
/// </summary>
/// <param name="P">Point</param>
public override void Double(ref PointOnCurve P)
{
if (!P.IsHomogeneous)
{
P.Z = BigInteger.One;
}
BigInteger A = this.modP.Add(P.X, P.Y);
BigInteger B = this.modP.Multiply(A, A);
BigInteger C = this.modP.Multiply(P.X, P.X);
BigInteger D = this.modP.Multiply(P.Y, P.Y);
BigInteger E = this.modP.Add(C, D);
BigInteger H = this.modP.Multiply(P.Z, P.Z);
BigInteger J = this.modP.Subtract(E, H << 1);
P.X = this.modP.Multiply(B - E, J);
P.Y = this.modP.Multiply(E, C - D);
P.Z = this.modP.Multiply(E, J);
}
/// <summary>
/// Encodes a point on the curve.
/// </summary>
/// <param name="Point">Normalized point to encode.</param>
/// <returns>Encoded point.</returns>
public virtual byte[] Encode(PointOnCurve Point)
{
byte[] X = Point.X.ToByteArray();
byte[] Y = Point.Y.ToByteArray();
if (X.Length != this.orderBytes)
{
Array.Resize <byte>(ref X, this.orderBytes);
}
if (Y.Length != this.orderBytes)
{
Array.Resize <byte>(ref Y, this.orderBytes);
}
byte[] Result = new byte[this.orderBytes << 1];
Array.Copy(X, 0, Result, 0, this.orderBytes);
Array.Copy(Y, 0, Result, this.orderBytes, this.orderBytes);
return(Result);
}
/// <summary>
/// Performs the scalar multiplication of <paramref name="N"/>*<paramref name="P"/>.
/// </summary>
/// <param name="N">Scalar, in binary, little-endian form.</param>
/// <param name="P">Point</param>
/// <param name="Normalize">If normalized output is expected.</param>
/// <returns><paramref name="N"/>*<paramref name="P"/></returns>
public virtual PointOnCurve ScalarMultiplication(byte[] N, PointOnCurve P, bool Normalize)
{
PointOnCurve Result = this.Zero;
int i, c = N.Length;
byte b, Bit;
for (i = 0; i < c; i++)
{
b = N[i];
for (Bit = 1; Bit != 0; Bit <<= 1)
{
if ((b & Bit) != 0)
{
this.AddTo(ref Result, P);
}
this.Double(ref P);
}
}
return(Result);
}
/// <summary>
/// Encodes a point on the curve in accordance with §5.1.2 of RFC 8032.
/// </summary>
/// <param name="P">Point</param>
/// <param name="Curve">Edwards curve.</param>
/// <returns>Encoding</returns>
public static byte[] Encode(PointOnCurve P, EdwardsCurveBase Curve)
{
int ScalarBits = Curve.CoordinateBits;
int ScalarBytes = (ScalarBits + 9) >> 3;
byte[] y = P.Y.ToByteArray();
if (y.Length != ScalarBytes)
{
Array.Resize <byte>(ref y, ScalarBytes);
}
byte[] x = P.X.ToByteArray();
int Msb = (ScalarBits + 1) & 7;
byte Mask = (byte)(0xff >> (8 - Msb));
y[ScalarBytes - 1] &= Mask;
if ((x[0] & 1) != 0)
{
y[ScalarBytes - 1] |= 0x80; // Always MSB
}
return(y);
}
/// <summary>
/// Abstract base class for elliptic curves.
/// </summary>
/// <param name="BasePoint">Base-point.</param>
/// <param name="Order">Order of base-point.</param>
/// <param name="Cofactor">Cofactor of curve.</param>
public EllipticCurve(PointOnCurve BasePoint, BigInteger Order, int Cofactor)
: this(BasePoint, Order, Cofactor, null)
{
}
/// <summary> /// Doubles a point on the curve. /// </summary> /// <param name="P">Point</param> public abstract void Double(ref PointOnCurve P);
/// <summary> /// Adds <paramref name="Q"/> to <paramref name="P"/>. /// </summary> /// <param name="P">Point 1.</param> /// <param name="Q">Point 2.</param> /// <returns>P+Q</returns> public abstract void AddTo(ref PointOnCurve P, PointOnCurve Q);
/// <summary>
/// Performs the scalar multiplication of <paramref name="N"/>*<paramref name="P"/>.
/// </summary>
/// <param name="N">Scalar</param>
/// <param name="P">Point</param>
/// <param name="Normalize">If normalized output is expected.</param>
/// <returns><paramref name="N"/>*<paramref name="P"/></returns>
public PointOnCurve ScalarMultiplication(BigInteger N, PointOnCurve P, bool Normalize)
{
return(this.ScalarMultiplication(N.ToByteArray(), P, Normalize));
}
/// <summary>
/// Encodes a point on the curve.
/// </summary>
/// <param name="Point">Normalized point to encode.</param>
/// <returns>Encoded point.</returns>
public override byte[] Encode(PointOnCurve Point)
{
return(EdDSA.Encode(Point, this));
}
/// <summary>
/// Base class of Twisted Edwards curves (-x²+y²=1+dx²y²) over a prime field.
/// </summary>
/// <param name="Prime">Prime base of field.</param>
/// <param name="BasePoint">Base-point in (X,Y) coordinates.</param>
/// <param name="d">Edwards curve coefficient</param>
/// <param name="Order">Order of base-point.</param>
/// <param name="Cofactor">Cofactor of curve.</param>
public EdwardsCurveBase(BigInteger Prime, PointOnCurve BasePoint,
BigInteger d, BigInteger Order, int Cofactor)
: this(Prime, BasePoint, d, Order, Cofactor, null)
{
}
/// <summary>
/// Negates a point on the curve.
/// </summary>
/// <param name="P">Point</param>
public void Negate(ref PointOnCurve P)
{
P.X = this.p - P.X;
}
/// <summary>
/// Base class of Elliptic curves over a prime field.
/// </summary>
/// <param name="Prime">Prime base of field.</param>
/// <param name="BasePoint">Base-point.</param>
/// <param name="Order">Order of base-point.</param>
/// <param name="Cofactor">Cofactor of curve.</param>
public PrimeFieldCurve(BigInteger Prime, PointOnCurve BasePoint, BigInteger Order,
int Cofactor)
: this(Prime, BasePoint, Order, Cofactor, null)
{
}
/// <summary>
/// Base class of Edwards curves (x²+y²=1+dx²y²) over a prime field.
/// </summary>
/// <param name="Prime">Prime base of field.</param>
/// <param name="BasePoint">Base-point in (X,Y) coordinates.</param>
/// <param name="d">Coefficient in the curve equation (x²+y²=1+dx²y²)</param>
/// <param name="Order">Order of base-point.</param>
/// <param name="Cofactor">Cofactor of curve.</param>
/// <param name="Secret">Secret.</param>
public EdwardsCurve(BigInteger Prime, PointOnCurve BasePoint, BigInteger d,
BigInteger Order, int Cofactor, byte[] Secret)
: base(Prime, BasePoint, d, Order, Cofactor, Secret)
{
this.p34 = (this.p - 3) / 4;
}
