SimpleDERReader.java :  » App » sshtunnel » com » trilead » ssh2 » crypto » Android Open Source

package com.trilead.ssh2.crypto;

import java.io.IOException;
import java.math.BigInteger;

/**
 * SimpleDERReader.
 * 
 * @author Christian Plattner, plattner@trilead.com
 * @version $Id: SimpleDERReader.java,v 1.1 2007/10/15 12:49:56 cplattne Exp $
 */
public class SimpleDERReader {
  byte[] buffer;
  int pos;
  int count;

  public SimpleDERReader(byte[] b) {
    resetInput(b);
  }

  public SimpleDERReader(byte[] b, int off, int len) {
    resetInput(b, off, len);
  }

  public int available() {
    return count;
  }

  public int ignoreNextObject() throws IOException {
    int type = readByte() & 0xff;

    int len = readLength();

    if ((len < 0) || len > available())
      throw new IOException("Illegal len in DER object (" + len + ")");

    readBytes(len);

    return type;
  }

  private byte readByte() throws IOException {
    if (count <= 0)
      throw new IOException("DER byte array: out of data");
    count--;
    return buffer[pos++];
  }

  private byte[] readBytes(int len) throws IOException {
    if (len > count)
      throw new IOException("DER byte array: out of data");

    byte[] b = new byte[len];

    System.arraycopy(buffer, pos, b, 0, len);

    pos += len;
    count -= len;

    return b;
  }

  public BigInteger readInt() throws IOException {
    int type = readByte() & 0xff;

    if (type != 0x02)
      throw new IOException("Expected DER Integer, but found type "
          + type);

    int len = readLength();

    if ((len < 0) || len > available())
      throw new IOException("Illegal len in DER object (" + len + ")");

    byte[] b = readBytes(len);

    BigInteger bi = new BigInteger(b);

    return bi;
  }

  private int readLength() throws IOException {
    int len = readByte() & 0xff;

    if ((len & 0x80) == 0)
      return len;

    int remain = len & 0x7F;

    if (remain == 0)
      return -1;

    len = 0;

    while (remain > 0) {
      len = len << 8;
      len = len | (readByte() & 0xff);
      remain--;
    }

    return len;
  }

  public byte[] readOctetString() throws IOException {
    int type = readByte() & 0xff;

    if (type != 0x04)
      throw new IOException("Expected DER Octetstring, but found type "
          + type);

    int len = readLength();

    if ((len < 0) || len > available())
      throw new IOException("Illegal len in DER object (" + len + ")");

    byte[] b = readBytes(len);

    return b;
  }

  public byte[] readSequenceAsByteArray() throws IOException {
    int type = readByte() & 0xff;

    if (type != 0x30)
      throw new IOException("Expected DER Sequence, but found type "
          + type);

    int len = readLength();

    if ((len < 0) || len > available())
      throw new IOException("Illegal len in DER object (" + len + ")");

    byte[] b = readBytes(len);

    return b;
  }

  public void resetInput(byte[] b) {
    resetInput(b, 0, b.length);
  }

  public void resetInput(byte[] b, int off, int len) {
    buffer = b;
    pos = off;
    count = len;
  }

}