/// <summary>
/// Parses an elliptic curve point.
/// </summary>
/// <param name="data">octet data</param>
/// <param name="ec">elliptic curve domain parameters</param>
/// <param name="p">an elliptic curve point object</param>
/// <returns>true if parsing and validation succeeded</returns>
public static bool Parse(byte[] data, EllipticCurve ec, out ECPoint p) {
if (IsZero(data)) {
// point at infinity
p = null;
return false;
}
if (data.Length < 2) {
// invalid length
p = null;
return false;
}
if (data[0] == 0x04) {
ECPoint tmp = ParseUncompressed(data);
if (tmp == null) {
p = null;
return false;
}
if (!ec.ValidatePoint(tmp)) {
p = null;
return false;
}
p = tmp;
p.Validated = true;
return true;
}
// Compressed form of EC point is not supported.
// OpenSSL, which is used by OpenSSH for cryptography, disables
// EC point compression by default due to the patent reason.
p = null;
return false;
}
/// <summary>
/// Chooses a hashing algorithm.
/// </summary>
/// <remarks>
/// Hashing algorithm is determined according to the curve size as described in RFC5656.
/// </remarks>
/// <param name="curve">elliptic curve</param>
/// <returns>new instance of the hashing algorithm</returns>
public static HashAlgorithm Choose(EllipticCurve curve) {
int orderBits = curve.Order.BitCount();
if (orderBits <= 256) {
return new SHA256CryptoServiceProvider();
}
else if (orderBits <= 384) {
return new SHA384CryptoServiceProvider();
}
else {
return new SHA512CryptoServiceProvider();
}
}
/// <summary>
/// Hash data for signing
/// </summary>
/// <param name="data">data to be hashed</param>
/// <param name="curve">elliptic curve for determining hashing algorithm</param>
/// <returns></returns>
internal byte[] HashForSigning(byte[] data, EllipticCurve curve) {
byte[] hash;
using (var hashAlgorithm = ECDSAHashAlgorithmChooser.Choose(curve)) {
hash = hashAlgorithm.ComputeHash(data);
}
return ExtractLeftBits(hash, curve.Order.BitCount());
}
/// <summary>
/// Constructor
/// </summary>
/// <param name="curve">elliptic curve</param>
/// <param name="publicKey">public key</param>
/// <param name="privateKey">private key</param>
public ECDSAKeyPair(EllipticCurve curve, ECDSAPublicKey publicKey, BigInteger privateKey) {
_curve = curve;
_publicKey = publicKey;
_privateKey = privateKey;
}
public ECDSAPublicKey(EllipticCurve curve, ECPoint point) {
_curve = curve;
_point = point;
}
