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package org.jolokia.jvmagent.security;/*
 * 
 * Copyright 2015
 *
 * 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.
 */

import java.io.*;
import java.math.BigInteger;
import java.security.spec.RSAPrivateCrtKeySpec;

/**
 * This code is inspired and taken over from net.auth.core:oauth
 * (albeit in a highly stripped variation):
 * 
 * Source is from http://oauth.googlecode.com/svn/code/java/ which is licensed
 * under the APL (http://oauth.googlecode.com/svn/code/java/LICENSE.txt)
 * 
 * All credits go to the original author (zhang)
 *
 * @author roland
 * @since 30/09/15
 */
class PKCS1Util {

    private PKCS1Util() {
    }

    public static RSAPrivateCrtKeySpec decodePKCS1(byte[] keyBytes) throws IOException {
        DerParser parser = new DerParser(keyBytes);
        Asn1Object sequence = parser.read();
        sequence.validateSequence();
        parser = new DerParser(sequence.getValue());
        parser.read();

        return new RSAPrivateCrtKeySpec(next(parser), next(parser),
                                        next(parser), next(parser),
                                        next(parser), next(parser),
                                        next(parser), next(parser));
    }

    // ==========================================================================================

    private static BigInteger next(DerParser parser) throws IOException {
        return parser.read().getInteger();
    }

    static class DerParser {

        private InputStream in;

        DerParser(byte[] bytes) throws IOException {
            this.in = new ByteArrayInputStream(bytes);
        }

        Asn1Object read() throws IOException {
            int tag = in.read();

            if (tag == -1) {
                throw new IOException("Invalid DER: stream too short, missing tag");
            }

            int length = getLength();
            byte[] value = new byte[length];
            if (in.read(value) < length) {
                throw new IOException("Invalid DER: stream too short, missing value");
            }

            return new Asn1Object(tag, value);
        }

        private int getLength() throws IOException {
            int i = in.read();
            if (i == -1) {
                throw new IOException("Invalid DER: length missing");
            }

            if ((i & ~0x7F) == 0) {
                return i;
            }

            int num = i & 0x7F;
            if (i >= 0xFF || num > 4) {
                throw new IOException("Invalid DER: length field too big ("
                                      + i + ")");
            }

            byte[] bytes = new byte[num];
            if (in.read(bytes) < num) {
                throw new IOException("Invalid DER: length too short");
            }

            return new BigInteger(1, bytes).intValue();
        }
    }

    static class Asn1Object {

        private final int type;
        private final byte[] value;
        private final int tag;

        public Asn1Object(int tag, byte[] value) {
            this.tag = tag;
            this.type = tag & 0x1F;
            this.value = value;
        }

        public byte[] getValue() {
            return value;
        }

        BigInteger getInteger() throws IOException {
            if (type != 0x02) {
                throw new IOException("Invalid DER: object is not integer"); //$NON-NLS-1$
            }
            return new BigInteger(value);
        }

        void validateSequence() throws IOException {
            if (type != 0x10) {
                throw new IOException("Invalid DER: not a sequence");
            }
            if ((tag & 0x20) != 0x20) {
                throw new IOException("Invalid DER: can't parse primitive entity");
            }
        }
    }
}