SHA1Signature.java

/*
 * Copyright 2012 Thomas Bocek
 *
 * 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 net.tomp2p.message;

import java.io.IOException;

import net.tomp2p.peers.Number160;

/**
 * Bare minimun ASN.1 encoder and decoder for the signature.
 * 
 * @author Thomas Bocek
 * 
 */
public class SHA1Signature {
    private Number160 number1;

    private Number160 number2;

    public SHA1Signature() {
    }

    public SHA1Signature(Number160 number1, Number160 number2) {
        this.number1 = number1;
        this.number2 = number2;
    }

    public void decode(byte[] encodedData) throws IOException {
        if (encodedData[0] != 0x30) {
            throw new IOException("expected sequence with value 48, but got " + encodedData[0]);
        }
        int seqLen = encodedData[1];
        if (seqLen > 127) {
            throw new IOException("cannot handle seq legth > than 127, got " + seqLen);
        }
        if (encodedData[2] != 0x02) {
            throw new IOException("expected sequence with value 2, but got " + encodedData[2]);
        }
        int intLen1 = encodedData[3];
        if (intLen1 > 127) {
            throw new IOException("cannot handle int legth > than 127, got " + intLen1);
        }
        number1 = encodeNumber(encodedData, 4, intLen1);
        //
        if (encodedData[4 + intLen1] != 0x02) {
            throw new IOException("expected sequence with value 2, but got " + encodedData[4 + intLen1]);
        }
        int intLen2 = encodedData[5 + intLen1];
        if (intLen2 > 127) {
            throw new IOException("cannot handle int legth > than 127, got " + intLen2);
        }
        number2 = encodeNumber(encodedData, 6 + intLen1, intLen2);
    }

    private Number160 encodeNumber(byte[] encodedData, int offset, int len) throws IOException {
        if (len > 20) {
            int bias = len - 20;
            for (int i = 0; i < bias; i++) {
                if (encodedData[offset + i] != 0) {
                    throw new IOException("we did not expect such a large number, it should be 160bit");
                }
            }
            return new Number160(encodedData, offset + bias, 20);
        } else {
            return new Number160(encodedData, offset, len);
        }
    }

    public byte[] encode() throws IOException {
        byte me[] = new byte[2 + (2 * (20 + 2))];
        me[0] = 0x30;
        me[1] = 2 * (20 + 2);
        me[2] = 0x02;
        me[3] = 20;
        number1.toByteArray(me, 4);
        me[24] = 0x02;
        me[25] = 20;
        number2.toByteArray(me, 26);
        return me;
    }

    public Number160 getNumber1() {
        return number1;
    }

    public Number160 getNumber2() {
        return number2;
    }
}