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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 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++];
}
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 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 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;
}
}
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