public EccPoint Add(EccPoint pointA, EccPoint pointB)
{
// Any point added to infinity is itself
if (pointA.Infinity)
{
return(pointB);
}
// Any point added to infinity is itself
if (pointB.Infinity)
{
return(pointA);
}
// Any point added to its inverse is infinity
if (pointA.Equals(Negate(pointB)))
{
return(new EccPoint("infinity"));
}
// Cannot add two identical points, use Double instead
if (pointA.Equals(pointB))
{
return(Double(pointA));
}
var numerator = _operator.Subtract(pointB.Y, pointA.Y);
var denominator = _operator.Subtract(pointB.X, pointA.X);
var lambda = _operator.Divide(numerator, denominator);
var x = _operator.Subtract(_operator.Subtract(_operator.Multiply(lambda, lambda), pointA.X), pointB.X);
var y = _operator.Subtract(_operator.Multiply(_operator.Subtract(pointA.X, x), lambda), pointA.Y);
return(new EccPoint(x, y));
}
/// <summary>
/// Based on the Fixed-base comb method (Algorithm 17 from https://link.springer.com/content/pdf/10.1007/3-540-44499-8_1.pdf)
/// </summary>
/// <param name="scalar"></param>
/// <returns></returns>
private EccPoint FastMultiply(BigInteger scalar)
{
var width = 4;
var degree = FieldSizeQ.ExactBitLength();
var d = degree.CeilingDivide(width);
var scalarBits = new BitString(scalar, degree).Bits;
var point = new EccPoint("infinity");
for (var i = d - 1; i >= 0; i--)
{
point = Double(point);
var index = 0;
for (var j = width - 1; j >= 0; j--)
{
index *= 2;
if (i + d * j >= degree)
{
continue;
}
if (scalarBits[i + d * j])
{
index++;
}
}
if (index != 0)
{
point = Add(point, _precomputedMultiplication[index]);
}
}
return(point);
}
public bool PointExistsOnCurve(EccPoint point)
{
if (point.Infinity)
{
return(true);
}
// Point is out of bounds
if (!PointExistsInField(point))
{
return(false);
}
var ySquared = _operator.Multiply(point.Y, point.Y);
var xTimesY = _operator.Multiply(point.X, point.Y);
var lhs = _operator.Add(ySquared, xTimesY);
var xCubed = _operator.Multiply(_operator.Multiply(point.X, point.X), point.X);
var xSquared = _operator.Multiply(point.X, point.X);
var aTimesXSquares = _operator.Multiply(CoefficientA, xSquared);
var rhs = _operator.Add(_operator.Add(xCubed, aTimesXSquares), CoefficientB);
// y^2 + xy = x^3 + ax^2 + b
return(lhs == rhs);
}
public static bool PerformEccPublicKeyValidation(IEccCurve curve, EccPoint publicKey, bool shouldThrow = false)
{
if (!curve.PointExistsOnCurve(publicKey))
{
if (shouldThrow)
{
throw new Exception("public key does not exist on curve");
}
return(false);
}
var n = curve.OrderN;
var nQ = curve.Multiply(publicKey, n);
if (!nQ.Infinity)
{
if (shouldThrow)
{
throw new Exception("public key validation error");
}
return(false);
}
return(true);
}
public EccPoint Negate(EccPoint point)
{
if (point.Infinity)
{
return(point);
}
return(new EccPoint(point.X, _operator.Add(point.X, point.Y)));
}
public EccPoint Subtract(EccPoint pointA, EccPoint pointB)
{
if (pointA.Infinity || pointB.Infinity)
{
return(pointA);
}
return(Add(pointA, Negate(pointB)));
}
public EccPoint Negate(EccPoint point)
{
if (point.Infinity)
{
return(point);
}
// Negate the point, - (x, y) == (x, -y), but -1 * y (mod q) == q - y
return(new EccPoint(point.X, _operator.Negate(point.Y)));
}
public PrimeCurve(Curve curveName, BigInteger p, BigInteger b, EccPoint g, BigInteger n)
{
CurveName = curveName;
FieldSizeQ = p;
CoefficientB = b;
BasePointG = g;
OrderN = n;
_operator = new PrimeFieldOperator(p);
}
void EcdhSample(Tpm2 tpm, TestContext testCtx)
{
//
// Peer A (e.g. local machine):
//
// Template for an ECC key with the ECDH scheme:
var inPub = new TpmPublic(TpmAlgId.Sha256,
ObjectAttr.Decrypt | ObjectAttr.UserWithAuth | ObjectAttr.SensitiveDataOrigin,
null,
new EccParms(new SymDefObject(), new SchemeEcdh(TpmAlgId.Sha256),
EccCurve.NistP256, new NullKdfScheme()),
new EccPoint());
// Boilerplate stuff
var pcrSel = new PcrSelection[0];
CreationData crData;
byte[] crHash;
TkCreation crTk;
// Create a key for ECDH
TpmPublic pubA;
TpmHandle hKeyA = tpm.CreatePrimary(TpmRh.Owner, new SensitiveCreate(), inPub, null, new PcrSelection[0],
out pubA, out crData, out crHash, out crTk);
//
// Peer B (e.g. remote machine):
//
// Receives 'pubA' from peer A
// Load public key
TpmHandle hPubKeyA = tpm.LoadExternal(null, pubA, TpmRh.Owner);
// Create shared secret 'zB', and a public ECC point for exchange
EccPoint ephPubPt;
EccPoint zB = tpm.EcdhKeyGen(hPubKeyA, out ephPubPt);
tpm.FlushContext(hPubKeyA);
//
// Peer A again:
//
// Receives 'ephPubPt' from peer B
// A full key is required here
EccPoint zA = tpm.EcdhZGen(hKeyA, ephPubPt);
testCtx.AssertEqual("SharedSecret", zA, zB);
tpm.FlushContext(hKeyA);
} // EcdhSample
public bool PointExistsInField(EccPoint point)
{
var m = FieldSizeQ.ExactBitLength();
if (point.X.ExactBitLength() == m || point.Y.ExactBitLength() == m)
{
return(false);
}
return(true);
}
public BinaryCurve(Curve curveName, BigInteger f, BigInteger a, BigInteger b, EccPoint basis, BigInteger n, int h, List <EccPoint> points = null)
{
CurveName = curveName;
FieldSizeQ = f;
CoefficientA = a;
CoefficientB = b;
BasePointG = basis;
OrderN = n;
CofactorH = h;
_operator = new GaloisFieldOperator(f);
_precomputedMultiplication = points ?? new List <EccPoint>();
}
public bool PointExistsInField(EccPoint point)
{
if (point.X < 0 || point.X > FieldSizeQ - 1)
{
return(false);
}
if (point.Y < 0 || point.Y > FieldSizeQ - 1)
{
return(false);
}
return(true);
}
public EccPoint Multiply(EccPoint startPoint, BigInteger scalar)
{
// Intentional normal modulo, this is what CAVS does
scalar %= OrderN;
if (startPoint.Equals(BasePointG) && HasPrecomputedValues)
{
return(FastMultiply(scalar));
}
else
{
return(Multiply(startPoint, new NonAdjacentBitString(scalar)));
}
}
public EccPoint Double(EccPoint point)
{
if (point.X == 0 || point.Infinity)
{
return(point);
}
var numerator = point.Y;
var denominator = point.X;
var lambda = _operator.Add(_operator.Multiply(numerator, _operator.Inverse(denominator)), point.X);
var x = _operator.Add(_operator.Add(_operator.Multiply(lambda, lambda), lambda), CoefficientA);
var y = _operator.Add(_operator.Multiply(_operator.Add(lambda, 1), x), _operator.Multiply(point.X, point.X));
return(new EccPoint(x, y));
}
public bool PointExistsOnCurve(EccPoint point)
{
if (point.Infinity)
{
return(true);
}
// Point is out of bounds
if (!PointExistsInField(point))
{
return(false);
}
var lhs = _operator.Multiply(point.Y, point.Y);
var rhs = _operator.Add(_operator.Add(_operator.Multiply(_operator.Multiply(point.X, point.X), point.X), _operator.Multiply(CoefficientA, point.X)), CoefficientB);
return(lhs == rhs);
}
public EccPoint Add(EccPoint pointA, EccPoint pointB)
{
// Any point added to infinity is itself
if (pointA.Infinity)
{
return(pointB);
}
// Any point added to infinity is itself
if (pointB.Infinity)
{
return(pointA);
}
// Any point added to its inverse is infinity
if (pointA.Equals(Negate(pointB)))
{
return(new EccPoint("infinity"));
}
// Cannot add two identical points, use Double instead
if (pointA.Equals(pointB))
{
return(Double(pointA));
}
var numerator = _operator.Add(pointA.Y, pointB.Y);
var denominator = _operator.Add(pointA.X, pointB.X);
if (denominator == 0)
{
return(new EccPoint("infinity"));
}
var lambda = _operator.Multiply(numerator, _operator.Inverse(denominator));
// x = lambda * lambda + lambda + x1 + x2 + a
var x = _operator.Add(_operator.Add(_operator.Add(_operator.Add(_operator.Multiply(lambda, lambda), lambda), pointA.X), pointB.X), CoefficientA);
// y = lambda * (x1 + x3) + x + y1
var y = _operator.Add(_operator.Add(_operator.Multiply(_operator.Add(pointA.X, x), lambda), x), pointA.Y);
return(new EccPoint(x, y));
}
public static SchemeEcdaa PrepareEcdaaScheme(Tpm2 tpm, TpmHandle signKey,
ISigSchemeUnion scheme)
{
var schemeEcdaa = scheme as SchemeEcdaa;
if (schemeEcdaa != null)
{
byte[] name, qualName;
var keyPub = tpm.ReadPublic(signKey, out name, out qualName);
ushort counter = 0;
EccPoint l, E;
EccPoint PP = keyPub.unique as EccPoint;
tpm.Commit(signKey, PP, null, null, out l, out E, out counter);
schemeEcdaa.count = counter;
}
return(schemeEcdaa);
}
private EccPoint Multiply(EccPoint startPoint, NonAdjacentBitString nafBs)
{
var point = new EccPoint("infinity");
var naBits = nafBs.Bits;
for (var i = naBits.Length - 1; i >= 0; i--)
{
point = Double(point);
if (naBits[i] == 1)
{
point = Add(point, startPoint);
}
else if (naBits[i] == -1)
{
point = Subtract(point, startPoint);
}
}
return(point);
}
public EccPoint Double(EccPoint point)
{
if ((point.X == 0 && point.Y == 0) || point.Infinity)
{
return(point);
}
if (point.Y == 0)
{
throw new ArgumentException("Cannot double a point with y = 0");
}
var numerator = _operator.Add(_operator.Multiply(_operator.Multiply(3, point.X), point.X), CoefficientA);
var denominator = _operator.Multiply(2, point.Y);
var lambda = _operator.Divide(numerator, denominator);
var x = _operator.Subtract(_operator.Multiply(lambda, lambda), _operator.Multiply(2, point.X));
var y = _operator.Subtract(_operator.Multiply(_operator.Subtract(point.X, x), lambda), point.Y);
return(new EccPoint(x, y));
}
public EccPoint Multiply(EccPoint startPoint, BigInteger scalar)
{
// Find scalar within group and convert to NABS, normal modulo here, not on the field, like CAVS
return(Multiply(startPoint, new NonAdjacentBitString(scalar % OrderN)));
}
public void ShouldReturnExpectedValidationResultEcc(string label, Curve curveEnum, EccPoint publicKey, bool shouldPassValidation)
{
var curve = new EccCurveFactory().GetCurve(curveEnum);
var result = KeyValidationHelper.PerformEccPublicKeyValidation(curve, publicKey, false);
Assert.AreEqual(shouldPassValidation, result);
}
public EccPoint Subtract(EccPoint pointA, EccPoint pointB)
{
return(Add(pointA, Negate(pointB)));
}
