/*
 * ConnectBot: simple, powerful, open-source SSH client for Android
 * Copyright 2007 Kenny Root, Jeffrey Sharkey
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.five_ten_sg.connectbot.util;

import java.io.IOException;
import java.math.BigInteger;
import java.security.AlgorithmParameters;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.interfaces.DSAParams;
import java.security.interfaces.DSAPrivateKey;
import java.security.interfaces.DSAPublicKey;
import java.security.interfaces.ECPrivateKey;
import java.security.interfaces.ECPublicKey;
import java.security.interfaces.RSAPrivateCrtKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.DSAPublicKeySpec;
import java.security.spec.ECParameterSpec;
import java.security.spec.ECPoint;
import java.security.spec.ECPublicKeySpec;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.InvalidParameterSpecException;
import java.security.spec.KeySpec;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.RSAPublicKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Arrays;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.EncryptedPrivateKeyInfo;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.PBEParameterSpec;
import javax.crypto.spec.SecretKeySpec;

import org.keyczar.jce.EcCore;

import com.five_ten_sg.connectbot.bean.PubkeyBean;
import android.util.Log;

import ch.ethz.ssh2.crypto.Base64;
import ch.ethz.ssh2.crypto.SimpleDERReader;
import ch.ethz.ssh2.signature.DSASHA1Verify;
import ch.ethz.ssh2.signature.ECDSASHA2Verify;
import ch.ethz.ssh2.signature.RSASHA1Verify;

public class PubkeyUtils {
    private static final String TAG = "PubkeyUtils";

    public static final String PKCS8_START = "-----BEGIN PRIVATE KEY-----";
    public static final String PKCS8_END = "-----END PRIVATE KEY-----";

    // Size in bytes of salt to use.
    private static final int SALT_SIZE = 8;

    // Number of iterations for password hashing. PKCS#5 recommends 1000
    private static final int ITERATIONS = 1000;

    // Cannot be instantiated
    private PubkeyUtils() {
    }

    public static String formatKey(Key key) {
        String algo = key.getAlgorithm();
        String fmt = key.getFormat();
        byte[] encoded = key.getEncoded();
        return "Key[algorithm=" + algo + ", format=" + fmt +
               ", bytes=" + encoded.length + "]";
    }

    public static byte[] sha256(byte[] data) throws NoSuchAlgorithmException {
        return MessageDigest.getInstance("SHA-256").digest(data);
    }

    public static byte[] cipher(int mode, byte[] data, byte[] secret) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException {
        SecretKeySpec secretKeySpec = new SecretKeySpec(sha256(secret), "AES");
        Cipher c = Cipher.getInstance("AES");
        c.init(mode, secretKeySpec);
        return c.doFinal(data);
    }

    public static byte[] encrypt(byte[] cleartext, String secret) throws Exception {
        byte[] salt = new byte[SALT_SIZE];
        byte[] ciphertext = Encryptor.encrypt(salt, ITERATIONS, secret, cleartext);
        byte[] complete = new byte[salt.length + ciphertext.length];
        System.arraycopy(salt, 0, complete, 0, salt.length);
        System.arraycopy(ciphertext, 0, complete, salt.length, ciphertext.length);
        Arrays.fill(salt, (byte) 0x00);
        Arrays.fill(ciphertext, (byte) 0x00);
        return complete;
    }

    public static byte[] decrypt(byte[] saltAndCiphertext, String secret) throws Exception {
        try {
            byte[] salt = new byte[SALT_SIZE];
            byte[] ciphertext = new byte[saltAndCiphertext.length - salt.length];
            System.arraycopy(saltAndCiphertext, 0, salt, 0, salt.length);
            System.arraycopy(saltAndCiphertext, salt.length, ciphertext, 0, ciphertext.length);
            return Encryptor.decrypt(salt, ITERATIONS, secret, ciphertext);
        }
        catch (Exception e) {
            Log.d("decrypt", "Could not decrypt with new method", e);
            // We might be using the old encryption method.
            return cipher(Cipher.DECRYPT_MODE, saltAndCiphertext, secret.getBytes());
        }
    }

    public static byte[] getEncodedPrivate(PrivateKey pk, String secret) throws Exception {
        final byte[] encoded = pk.getEncoded();

        if (secret == null || secret.length() == 0) {
            return encoded;
        }

        return encrypt(pk.getEncoded(), secret);
    }

    public static PrivateKey decodePrivate(byte[] encoded, String keyType) throws NoSuchAlgorithmException, InvalidKeySpecException {
        PKCS8EncodedKeySpec privKeySpec = new PKCS8EncodedKeySpec(encoded);
        KeyFactory kf = KeyFactory.getInstance(keyType);
        return kf.generatePrivate(privKeySpec);
    }

    public static PrivateKey decodePrivate(byte[] encoded, String keyType, String secret) throws Exception {
        if (secret != null && secret.length() > 0)
            return decodePrivate(decrypt(encoded, secret), keyType);
        else
            return decodePrivate(encoded, keyType);
    }

    public static PublicKey decodePublic(byte[] encoded, String keyType) throws NoSuchAlgorithmException, InvalidKeySpecException {
        X509EncodedKeySpec pubKeySpec = new X509EncodedKeySpec(encoded);
        KeyFactory kf = KeyFactory.getInstance(keyType);
        return kf.generatePublic(pubKeySpec);
    }

    static String getAlgorithmForOid(String oid) throws NoSuchAlgorithmException {
        if ("1.2.840.10045.2.1".equals(oid)) {
            return "EC";
        }
        else if ("1.2.840.113549.1.1.1".equals(oid)) {
            return "RSA";
        }
        else if ("1.2.840.10040.4.1".equals(oid)) {
            return "DSA";
        }
        else {
            throw new NoSuchAlgorithmException("Unknown algorithm OID " + oid);
        }
    }

    static String getOidFromPkcs8Encoded(byte[] encoded) throws NoSuchAlgorithmException {
        if (encoded == null) {
            throw new NoSuchAlgorithmException("encoding is null");
        }

        try {
            SimpleDERReader reader = new SimpleDERReader(encoded);
            reader.resetInput(reader.readSequenceAsByteArray());
            reader.readInt();
            reader.resetInput(reader.readSequenceAsByteArray());
            return reader.readOid();
        }
        catch (IOException e) {
            Log.w(TAG, "Could not read OID", e);
            throw new NoSuchAlgorithmException("Could not read key", e);
        }
    }

    public static KeyPair recoverKeyPair(byte[] encoded) throws NoSuchAlgorithmException,
        InvalidKeySpecException {
        final String algo = getAlgorithmForOid(getOidFromPkcs8Encoded(encoded));
        final KeySpec privKeySpec = new PKCS8EncodedKeySpec(encoded);
        final KeyFactory kf = KeyFactory.getInstance(algo);
        final PrivateKey priv = kf.generatePrivate(privKeySpec);
        return new KeyPair(recoverPublicKey(kf, priv), priv);
    }


    static PublicKey recoverPublicKey(KeyFactory kf, PrivateKey priv)
    throws NoSuchAlgorithmException, InvalidKeySpecException {
        if (priv instanceof RSAPrivateCrtKey) {
            RSAPrivateCrtKey rsaPriv = (RSAPrivateCrtKey) priv;
            return kf.generatePublic(new RSAPublicKeySpec(rsaPriv.getModulus(), rsaPriv
                                     .getPublicExponent()));
        }
        else if (priv instanceof DSAPrivateKey) {
            DSAPrivateKey dsaPriv = (DSAPrivateKey) priv;
            DSAParams params = dsaPriv.getParams();
            // Calculate public key Y
            BigInteger y = params.getG().modPow(dsaPriv.getX(), params.getP());
            return kf.generatePublic(new DSAPublicKeySpec(y, params.getP(), params.getQ(), params
                                     .getG()));
        }
        else if (priv instanceof ECPrivateKey) {
            ECPrivateKey ecPriv = (ECPrivateKey) priv;
            ECParameterSpec params = ecPriv.getParams();
            // Calculate public key Y
            ECPoint generator = params.getGenerator();
            BigInteger[] wCoords = EcCore.multiplyPointA(new BigInteger[] { generator.getAffineX(),
                                   generator.getAffineY()
                                                                          }, ecPriv.getS(), params);
            ECPoint w = new ECPoint(wCoords[0], wCoords[1]);
            return kf.generatePublic(new ECPublicKeySpec(w, params));
        }
        else {
            throw new NoSuchAlgorithmException("Key type must be RSA, DSA, or EC");
        }
    }

    /*
     * OpenSSH compatibility methods
     */

    public static String convertToOpenSSHFormat(PublicKey pk, String origNickname) throws IOException, InvalidKeyException {
        String nickname = origNickname;

        if (nickname == null)
            nickname = "connectbot@android";

        if (pk instanceof RSAPublicKey) {
            String data = "ssh-rsa ";
            data += String.valueOf(Base64.encode(RSASHA1Verify.encodeSSHRSAPublicKey((RSAPublicKey) pk)));
            return data + " " + nickname;
        }
        else if (pk instanceof DSAPublicKey) {
            String data = "ssh-dss ";
            data += String.valueOf(Base64.encode(DSASHA1Verify.encodeSSHDSAPublicKey((DSAPublicKey) pk)));
            return data + " " + nickname;
        }
        else if (pk instanceof ECPublicKey) {
            ECPublicKey ecPub = (ECPublicKey) pk;
            String keyType = ECDSASHA2Verify.getCurveName(ecPub.getParams().getCurve().getField().getFieldSize());
            String keyData = String.valueOf(Base64.encode(ECDSASHA2Verify.encodeSSHECDSAPublicKey(ecPub)));
            return ECDSASHA2Verify.ECDSA_SHA2_PREFIX + keyType + " " + keyData + " " + nickname;
        }

        throw new InvalidKeyException("Unknown key type");
    }

    /*
     * OpenSSH compatibility methods
     */

    /**
     * @param pair
     * @return OpenSSH-encoded pubkey
     */
    public static byte[] extractOpenSSHPublic(KeyPair pair) {
        try {
            PublicKey pubKey = pair.getPublic();

            if (pubKey instanceof RSAPublicKey) {
                return RSASHA1Verify.encodeSSHRSAPublicKey((RSAPublicKey) pair.getPublic());
            }
            else if (pubKey instanceof DSAPublicKey) {
                return DSASHA1Verify.encodeSSHDSAPublicKey((DSAPublicKey) pair.getPublic());
            }
            else if (pubKey instanceof ECPublicKey) {
                return ECDSASHA2Verify.encodeSSHECDSAPublicKey((ECPublicKey) pair.getPublic());
            }
            else {
                return null;
            }
        }
        catch (IOException e) {
            return null;
        }
    }

    public static String exportPEM(PrivateKey key, String secret) throws NoSuchAlgorithmException, InvalidParameterSpecException, NoSuchPaddingException, InvalidKeyException, InvalidAlgorithmParameterException, InvalidKeySpecException, IllegalBlockSizeException, IOException {
        StringBuilder sb = new StringBuilder();
        byte[] data = key.getEncoded();
        sb.append(PKCS8_START);
        sb.append('\n');

        if (secret != null) {
            byte[] salt = new byte[8];
            SecureRandom random = new SecureRandom();
            random.nextBytes(salt);
            PBEParameterSpec defParams = new PBEParameterSpec(salt, 1);
            AlgorithmParameters params = AlgorithmParameters.getInstance(key.getAlgorithm());
            params.init(defParams);
            PBEKeySpec pbeSpec = new PBEKeySpec(secret.toCharArray());
            SecretKeyFactory keyFact = SecretKeyFactory.getInstance(key.getAlgorithm());
            Cipher cipher = Cipher.getInstance(key.getAlgorithm());
            cipher.init(Cipher.WRAP_MODE, keyFact.generateSecret(pbeSpec), params);
            byte[] wrappedKey = cipher.wrap(key);
            EncryptedPrivateKeyInfo pinfo = new EncryptedPrivateKeyInfo(params, wrappedKey);
            data = pinfo.getEncoded();
            sb.append("Proc-Type: 4,ENCRYPTED\n");
            sb.append("DEK-Info: DES-EDE3-CBC,");
            sb.append(encodeHex(salt));
            sb.append("\n\n");
        }

        int i = sb.length();
        sb.append(Base64.encode(data));

        for (i += 63; i < sb.length(); i += 64) {
            sb.insert(i, "\n");
        }

        sb.append('\n');
        sb.append(PKCS8_END);
        sb.append('\n');
        return sb.toString();
    }

    private static final char[] HEX_DIGITS = { '0', '1', '2', '3', '4', '5', '6',
                                               '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'
                                             };
    protected static String encodeHex(byte[] bytes) {
        final char[] hex = new char[bytes.length * 2];
        int i = 0;

        for (byte b : bytes) {
            hex[i++] = HEX_DIGITS[(b >> 4) & 0x0f];
            hex[i++] = HEX_DIGITS[b & 0x0f];
        }

        return String.valueOf(hex);
    }

    public static String getPubkeyString(PubkeyBean pubkey) {
        try {
            PublicKey pk = decodePublic(pubkey.getPublicKey(), pubkey.getType());
            return convertToOpenSSHFormat(pk, pubkey.getNickname());
        }
        catch (Exception e) {
            e.printStackTrace();
        }

        return null;
    }

    public static String getPrivkeyString(PubkeyBean pubkey, String passphrase) {
        String data = null;
        boolean imported = PubkeyDatabase.KEY_TYPE_IMPORTED.equals(pubkey.getType());

        if (imported)
            try {
                data = new String(pubkey.getPrivateKey());
            }
            catch (Exception e) {
                e.printStackTrace();
            }
        else {
            try {
                PrivateKey pk = null;

                if (passphrase == null)
                    pk = decodePrivate(pubkey.getPrivateKey(), pubkey.getType());
                else
                    pk = decodePrivate(pubkey.getPrivateKey(), pubkey.getType(), passphrase);

                data = exportPEM(pk, passphrase);
            }
            catch (Exception e) {
                e.printStackTrace();
            }
        }

        return data;
    }
}