// Extract EC parameters from public key
//
// ECparams UserID
//   will read file: UserID.public
//
import java.math.BigInteger;
import java.security.*;
import java.security.spec.*;
import java.security.interfaces.*;
import java.io.*;

public class ECparams
{
  public static void usage()
  {
    System.err.println( "Usage: ECparams UserID");
    System.exit(1);
  }

  public static void main(String args[]) throws Exception
  {
    String UserID = null;

    if( args.length != 1)
      usage();

    UserID = args[0];

   // get EC public key
   //
    String fname = UserID + ".public";
    File file = new File( fname);
    int len = (int) file.length();
    FileInputStream fis = new FileInputStream( file);
    byte b[] = new byte[len];
    int nbytes = fis.read( b);
    fis.close();
    if( nbytes != len) throw new Exception( "bad read: " + fname); 

    X509EncodedKeySpec x509 = new X509EncodedKeySpec( b);
    KeyFactory kf = KeyFactory.getInstance( "EC");
    ECPublicKey pub = (ECPublicKey) kf.generatePublic( x509);

  // extract parameters
  //
    ECParameterSpec params = pub.getParams();
    EllipticCurve c = params.getCurve();
    ECPoint G = params.getGenerator();
    BigInteger n = params.getOrder();
    int h = params.getCofactor();

    BigInteger A = c.getA();
    BigInteger B = c.getB();

    BigInteger GX = G.getAffineX();
    BigInteger GY = G.getAffineY();

    ECField f = c.getField();
    String type;
    BigInteger P = null;		// ECFieldFp
    BigInteger poly = null; int m = 0;	// ECFieldF2m

    if( f instanceof ECFieldFp)
    {
      type = "ECFieldFp";
      ECFieldFp fp = (ECFieldFp) f;
      P = fp.getP();
    }
    else
    {
      type = "ECFieldF2m";
      ECFieldF2m f2m = (ECFieldF2m) f;
      m = f2m.getM();
      poly = f2m.getReductionPolynomial();
      if( poly == null) poly = BigInteger.ZERO;
    }

    System.out.println( type);
    System.out.println( "G.X = " + GX.toString(16));
    System.out.println( "G.Y = " + GY.toString(16));
    System.out.println( "  A = " + A.toString(16));
    System.out.println( "  B = " + B.toString(16));
    System.out.println( "  n = " + n.toString(16));
    System.out.println( "  h = " + h);

    switch( type)
    {
      case "ECFieldFp":
	System.out.println( "  P = " + P.toString(16));
	break;
      case "ECFieldF2m":
	System.out.println( "  m = " + m);
	System.out.println( "poly= " + poly.toString(16));
	break;
    }
  }
}