SimpleDERReader.java

package ch.ethz.ssh2.crypto;

import java.io.IOException;

import net.rim.device.api.crypto.CryptoInteger;

import org.bbssh.ssh.v2.BigInteger;

/**
 * SimpleDERReader.
 * 
 * @author Christian Plattner, plattner@inf.ethz.ch
 * @version $Id: SimpleDERReader.java,v 1.3 2006/08/11 12:24:00 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 void resetInput(byte[] b) {
		resetInput(b, 0, b.length);
	}

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

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

	public 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 int available() {
		return count;
	}

	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 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;
	}

	public byte[] readIntAsByte() 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 + ")");

		return readBytes(len);

	}

	public CryptoInteger readCryptoInt() throws IOException {
		byte[] b = readIntAsByte();

		// remove leading 0s.
		int x = 0;
		while (x < b.length && b[x] == 0) {
			x++;
		}
		if (x == b.length) {
			return new CryptoInteger(0);
		}

		return new CryptoInteger(b, x, b.length - x);
	}

	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;
	}

	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 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;
	}

}