/**
 *
 */
package ch.ethz.ssh2.signature;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.math.BigInteger;
import java.security.InvalidKeyException;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.Signature;
import java.security.SignatureException;
import java.security.interfaces.ECPrivateKey;
import java.security.interfaces.ECPublicKey;
import java.security.spec.ECFieldFp;
import java.security.spec.ECParameterSpec;
import java.security.spec.ECPoint;
import java.security.spec.ECPublicKeySpec;
import java.security.spec.EllipticCurve;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.KeySpec;
import java.util.Map;
import java.util.TreeMap;

import ch.ethz.ssh2.log.Logger;
import ch.ethz.ssh2.packets.TypesReader;
import ch.ethz.ssh2.packets.TypesWriter;

/**
 * @author Kenny Root
 *
 */
public class ECDSASHA2Verify {
    private static final Logger log = Logger.getLogger(ECDSASHA2Verify.class);

    public static final String ECDSA_SHA2_PREFIX = "ecdsa-sha2-";

    private static final String NISTP256 = "nistp256";
    private static final String NISTP256_OID = "1.2.840.10045.3.1.7";
    private static final String NISTP384 = "nistp384";
    private static final String NISTP384_OID = "1.3.132.0.34";
    private static final String NISTP521 = "nistp521";
    private static final String NISTP521_OID = "1.3.132.0.35";

    private static final Map<String, ECParameterSpec> CURVES = new TreeMap<String, ECParameterSpec>();
    static {
        CURVES.put(NISTP256, EllipticCurves.nistp256);
        CURVES.put(NISTP384, EllipticCurves.nistp384);
        CURVES.put(NISTP521, EllipticCurves.nistp521);
    }

    private static final Map<Integer, String> CURVE_SIZES = new TreeMap<Integer, String>();
    static {
        CURVE_SIZES.put(256, NISTP256);
        CURVE_SIZES.put(384, NISTP384);
        CURVE_SIZES.put(521, NISTP521);
    }

    private static final Map<String, String> CURVE_OIDS = new TreeMap<String, String>();
    static {
        CURVE_OIDS.put(NISTP256_OID, NISTP256);
        CURVE_OIDS.put(NISTP384_OID, NISTP256);
        CURVE_OIDS.put(NISTP521_OID, NISTP256);
    }

    public static int[] getCurveSizes() {
        int[] keys = new int[CURVE_SIZES.size()];
        int i = 0;

        for (Integer n : CURVE_SIZES.keySet().toArray(new Integer[keys.length])) {
            keys[i++] = n;
        }

        return keys;
    }

    public static ECParameterSpec getCurveForSize(int size) {
        final String name = CURVE_SIZES.get(size);

        if (name == null) {
            return null;
        }

        return CURVES.get(name);
    }

    public static ECPublicKey decodeSSHECDSAPublicKey(byte[] key) throws IOException {
        TypesReader tr = new TypesReader(key);
        String key_format = tr.readString();

        if (key_format.startsWith(ECDSA_SHA2_PREFIX) == false)
            throw new IllegalArgumentException("This is not an ECDSA public key");

        String curveName = tr.readString();
        byte[] groupBytes = tr.readByteString();

        if (tr.remain() != 0)
            throw new IOException("Padding in ECDSA public key!");

        if (key_format.equals(ECDSA_SHA2_PREFIX + curveName) == false) {
            throw new IOException("Key format is inconsistent with curve name: " + key_format
                                  + " != " + curveName);
        }

        ECParameterSpec params = CURVES.get(curveName);

        if (params == null) {
            throw new IOException("Curve is not supported: " + curveName);
        }

        ECPoint group = ECDSASHA2Verify.decodeECPoint(groupBytes, params.getCurve());

        if (group == null) {
            throw new IOException("Invalid ECDSA group");
        }

        KeySpec keySpec = new ECPublicKeySpec(group, params);

        try {
            KeyFactory kf = KeyFactory.getInstance("EC");
            return (ECPublicKey) kf.generatePublic(keySpec);
        }
        catch (NoSuchAlgorithmException nsae) {
            IOException ioe = new IOException("No EC KeyFactory available");
            ioe.initCause(nsae);
            throw ioe;
        }
        catch (InvalidKeySpecException ikse) {
            IOException ioe = new IOException("No EC KeyFactory available");
            ioe.initCause(ikse);
            throw ioe;
        }
    }

    public static byte[] encodeSSHECDSAPublicKey(ECPublicKey key) throws IOException {
        TypesWriter tw = new TypesWriter();
        String curveName = getCurveName(key.getParams());
        String keyFormat = ECDSA_SHA2_PREFIX + curveName;
        tw.writeString(keyFormat);
        tw.writeString(curveName);
        byte[] encoded = encodeECPoint(key.getW(), key.getParams().getCurve());
        tw.writeString(encoded, 0, encoded.length);
        return tw.getBytes();
    }

    public static String getCurveName(ECParameterSpec params) throws IOException {
        int fieldSize = getCurveSize(params);
        final String curveName = getCurveName(fieldSize);

        if (curveName == null) {
            throw new IOException("invalid curve size " + fieldSize);
        }

        return curveName;
    }

    public static String getCurveName(int fieldSize) {
        String curveName = CURVE_SIZES.get(fieldSize);

        if (curveName == null) {
            return null;
        }

        return curveName;
    }

    public static int getCurveSize(ECParameterSpec params) {
        return params.getCurve().getField().getFieldSize();
    }

    public static ECParameterSpec getCurveForOID(String oid) {
        String name = CURVE_OIDS.get(oid);

        if (name == null)
            return null;

        return CURVES.get(name);
    }

    public static byte[] decodeSSHECDSASignature(byte[] sig) throws IOException {
        byte[] rsArray = null;
        TypesReader tr = new TypesReader(sig);
        String sig_format = tr.readString();

        if (sig_format.startsWith(ECDSA_SHA2_PREFIX) == false)
            throw new IOException("Peer sent wrong signature format");

        String curveName = sig_format.substring(ECDSA_SHA2_PREFIX.length());

        if (CURVES.containsKey(curveName) == false) {
            throw new IOException("Unsupported curve: " + curveName);
        }

        rsArray = tr.readByteString();

        if (tr.remain() != 0)
            throw new IOException("Padding in ECDSA signature!");

        byte[] rArray;
        byte[] sArray;
        {
            TypesReader rsReader = new TypesReader(rsArray);
            rArray = rsReader.readMPINT().toByteArray();
            sArray = rsReader.readMPINT().toByteArray();
        }
        int first = rArray.length;
        int second = sArray.length;

        /* We can't have the high bit set, so add an extra zero at the beginning if so. */
        if ((rArray[0] & 0x80) != 0) {
            first++;
        }

        if ((sArray[0] & 0x80) != 0) {
            second++;
        }

        /* Calculate total output length */
        ByteArrayOutputStream os = new ByteArrayOutputStream(6 + first + second);
        /* ASN.1 SEQUENCE tag */
        os.write(0x30);
        /* Size of SEQUENCE */
        writeLength(4 + first + second, os);
        /* ASN.1 INTEGER tag */
        os.write(0x02);
        /* "r" INTEGER length */
        writeLength(first, os);

        /* Copy in the "r" INTEGER */
        if (first != rArray.length) {
            os.write(0x00);
        }

        os.write(rArray);
        /* ASN.1 INTEGER tag */
        os.write(0x02);
        /* "s" INTEGER length */
        writeLength(second, os);

        /* Copy in the "s" INTEGER */
        if (second != sArray.length) {
            os.write(0x00);
        }

        os.write(sArray);
        return os.toByteArray();
    }

    private static final void writeLength(int length, OutputStream os) throws IOException {
        if (length <= 0x7F) {
            os.write(length);
            return;
        }

        int numOctets = 0;
        int lenCopy = length;

        while (lenCopy != 0) {
            lenCopy >>>= 8;
            numOctets++;
        }

        os.write(0x80 | numOctets);

        for (int i = (numOctets - 1) * 8; i >= 0; i -= 8) {
            os.write((byte)(length >> i));
        }
    }

    public static byte[] encodeSSHECDSASignature(byte[] sig, ECParameterSpec params) throws IOException {
        TypesWriter tw = new TypesWriter();
        String curveName = getCurveName(params);
        tw.writeString(ECDSA_SHA2_PREFIX + curveName);

        if ((sig[0] != 0x30) || (sig[1] != sig.length - 2) || (sig[2] != 0x02)) {
            throw new IOException("Invalid signature format");
        }

        int rLength = sig[3];

        if ((rLength + 6 > sig.length) || (sig[4 + rLength] != 0x02)) {
            throw new IOException("Invalid signature format");
        }

        int sLength = sig[5 + rLength];

        if (6 + rLength + sLength > sig.length) {
            throw new IOException("Invalid signature format");
        }

        byte[] rArray = new byte[rLength];
        byte[] sArray = new byte[sLength];
        System.arraycopy(sig, 4, rArray, 0, rLength);
        System.arraycopy(sig, 6 + rLength, sArray, 0, sLength);
        BigInteger r = new BigInteger(rArray);
        BigInteger s = new BigInteger(sArray);
        // Write the <r,s> to its own types writer.
        TypesWriter rsWriter = new TypesWriter();
        rsWriter.writeMPInt(r);
        rsWriter.writeMPInt(s);
        byte[] encoded = rsWriter.getBytes();
        tw.writeString(encoded, 0, encoded.length);
        return tw.getBytes();
    }

    public static byte[] generateSignature(byte[] message, ECPrivateKey pk) throws IOException {
        final String algo = getSignatureAlgorithmForParams(pk.getParams());

        try {
            Signature s = Signature.getInstance(algo);
            s.initSign(pk);
            s.update(message);
            return s.sign();
        }
        catch (NoSuchAlgorithmException e) {
            IOException ex = new IOException();
            ex.initCause(e);
            throw ex;
        }
        catch (InvalidKeyException e) {
            IOException ex = new IOException();
            ex.initCause(e);
            throw ex;
        }
        catch (SignatureException e) {
            IOException ex = new IOException();
            ex.initCause(e);
            throw ex;
        }
    }

    public static boolean verifySignature(byte[] message, byte[] ds, ECPublicKey dpk) throws IOException {
        final String algo = getSignatureAlgorithmForParams(dpk.getParams());

        try {
            Signature s = Signature.getInstance(algo);
            s.initVerify(dpk);
            s.update(message);
            return s.verify(ds);
        }
        catch (NoSuchAlgorithmException e) {
            IOException ex = new IOException("No such algorithm");
            ex.initCause(e);
            throw ex;
        }
        catch (InvalidKeyException e) {
            IOException ex = new IOException("No such algorithm");
            ex.initCause(e);
            throw ex;
        }
        catch (SignatureException e) {
            IOException ex = new IOException();
            ex.initCause(e);
            throw ex;
        }
    }

    private static String getSignatureAlgorithmForParams(ECParameterSpec params) {
        int size = getCurveSize(params);

        if (size <= 256) {
            return "SHA256withECDSA";
        }
        else if (size <= 384) {
            return "SHA384withECDSA";
        }
        else {
            return "SHA512withECDSA";
        }
    }

    public static String getDigestAlgorithmForParams(ECParameterSpec params) {
        int size = getCurveSize(params);

        if (size <= 256) {
            return "SHA256";
        }
        else if (size <= 384) {
            return "SHA384";
        }
        else {
            return "SHA512";
        }
    }

    /**
     * Decode an OctetString to EllipticCurvePoint according to SECG 2.3.4
     */
    public static ECPoint decodeECPoint(byte[] M, EllipticCurve curve) {
        if (M.length == 0) {
            return null;
        }

        // M has len 2 ceil(log_2(q)/8) + 1 ?
        int elementSize = (curve.getField().getFieldSize() + 7) / 8;

        if (M.length != 2 * elementSize + 1) {
            return null;
        }

        // step 3.2
        if (M[0] != 0x04) {
            return null;
        }

        // Step 3.3
        byte[] xp = new byte[elementSize];
        System.arraycopy(M, 1, xp, 0, elementSize);
        // Step 3.4
        byte[] yp = new byte[elementSize];
        System.arraycopy(M, 1 + elementSize, yp, 0, elementSize);
        ECPoint P = new ECPoint(new BigInteger(1, xp), new BigInteger(1, yp));
        // TODO check point 3.5
        // Step 3.6
        return P;
    }

    /**
     * Encode EllipticCurvePoint to an OctetString
     */
    public static byte[] encodeECPoint(ECPoint group, EllipticCurve curve) {
        // M has len 2 ceil(log_2(q)/8) + 1 ?
        int elementSize = (curve.getField().getFieldSize() + 7) / 8;
        byte[] M = new byte[2 * elementSize + 1];
        // Uncompressed format
        M[0] = 0x04;
        {
            byte[] affineX = removeLeadingZeroes(group.getAffineX().toByteArray());
            System.arraycopy(affineX, 0, M, 1 + elementSize - affineX.length, affineX.length);
        }
        {
            byte[] affineY = removeLeadingZeroes(group.getAffineY().toByteArray());
            System.arraycopy(affineY, 0, M, 1 + elementSize + elementSize - affineY.length,
                             affineY.length);
        }
        return M;
    }

    private static byte[] removeLeadingZeroes(byte[] input) {
        if (input[0] != 0x00) {
            return input;
        }

        int pos = 1;

        while (pos < input.length - 1 && input[pos] == 0x00) {
            pos++;
        }

        byte[] output = new byte[input.length - pos];
        System.arraycopy(input, pos, output, 0, output.length);
        return output;
    }

    public static class EllipticCurves {
        public static ECParameterSpec nistp256 = new ECParameterSpec(
            new EllipticCurve(
                new ECFieldFp(new BigInteger("FFFFFFFF00000001000000000000000000000000FFFFFFFFFFFFFFFFFFFFFFFF", 16)),
                new BigInteger("FFFFFFFF00000001000000000000000000000000FFFFFFFFFFFFFFFFFFFFFFFC", 16),
                new BigInteger("5ac635d8aa3a93e7b3ebbd55769886bc651d06b0cc53b0f63bce3c3e27d2604b", 16)),
            new ECPoint(new BigInteger("6B17D1F2E12C4247F8BCE6E563A440F277037D812DEB33A0F4A13945D898C296", 16),
                        new BigInteger("4FE342E2FE1A7F9B8EE7EB4A7C0F9E162BCE33576B315ECECBB6406837BF51F5", 16)),
            new BigInteger("FFFFFFFF00000000FFFFFFFFFFFFFFFFBCE6FAADA7179E84F3B9CAC2FC632551", 16),
            1);

        public static ECParameterSpec nistp384 = new ECParameterSpec(
            new EllipticCurve(
                new ECFieldFp(new BigInteger("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFFFF0000000000000000FFFFFFFF", 16)),
                new BigInteger("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFFFF0000000000000000FFFFFFFC", 16),
                new BigInteger("B3312FA7E23EE7E4988E056BE3F82D19181D9C6EFE8141120314088F5013875AC656398D8A2ED19D2A85C8EDD3EC2AEF", 16)),
            new ECPoint(new BigInteger("AA87CA22BE8B05378EB1C71EF320AD746E1D3B628BA79B9859F741E082542A385502F25DBF55296C3A545E3872760AB7", 16),
                        new BigInteger("3617DE4A96262C6F5D9E98BF9292DC29F8F41DBD289A147CE9DA3113B5F0B8C00A60B1CE1D7E819D7A431D7C90EA0E5F", 16)),
            new BigInteger("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFC7634D81F4372DDF581A0DB248B0A77AECEC196ACCC52973", 16),
            1);

        public static ECParameterSpec nistp521 = new ECParameterSpec(
            new EllipticCurve(
                new ECFieldFp(new BigInteger("01FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF", 16)),
                new BigInteger("01FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFC", 16),
                new BigInteger("0051953EB9618E1C9A1F929A21A0B68540EEA2DA725B99B315F3B8B489918EF109E156193951EC7E937B1652C0BD3BB1BF073573DF883D2C34F1EF451FD46B503F00", 16)),
            new ECPoint(new BigInteger("00C6858E06B70404E9CD9E3ECB662395B4429C648139053FB521F828AF606B4D3DBAA14B5E77EFE75928FE1DC127A2FFA8DE3348B3C1856A429BF97E7E31C2E5BD66", 16),
                        new BigInteger("011839296A789A3BC0045C8A5FB42C7D1BD998F54449579B446817AFBD17273E662C97EE72995EF42640C550B9013FAD0761353C7086A272C24088BE94769FD16650", 16)),
            new BigInteger("01FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFA51868783BF2F966B7FCC0148F709A5D03BB5C9B8899C47AEBB6FB71E91386409", 16),
            1);
    }
}