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package com.trilead.ssh2;
/**
* A <code>DHGexParameters</code> object can be used to specify parameters for
* the diffie-hellman group exchange.
* <p>
* Depending on which constructor is used, either the use of a
* <code>SSH_MSG_KEX_DH_GEX_REQUEST</code> or <code>SSH_MSG_KEX_DH_GEX_REQUEST_OLD</code>
* can be forced.
*
* @see Connection#setDHGexParameters(DHGexParameters)
* @author Christian Plattner, plattner@trilead.com
* @version $Id: DHGexParameters.java,v 1.1 2007/10/15 12:49:56 cplattne Exp $
*/
public class DHGexParameters
{
private final int min_group_len;
private final int pref_group_len;
private final int max_group_len;
private static final int MIN_ALLOWED = 1024;
private static final int MAX_ALLOWED = 8192;
/**
* Same as calling {@link #DHGexParameters(int, int, int) DHGexParameters(1024, 1024, 4096)}.
* This is also the default used by the Connection class.
*
*/
public DHGexParameters()
{
this(1024, 1024, 4096);
}
/**
* This constructor can be used to force the sending of a
* <code>SSH_MSG_KEX_DH_GEX_REQUEST_OLD</code> request.
* Internally, the minimum and maximum group lengths will
* be set to zero.
*
* @param pref_group_len has to be >= 1024 and <= 8192
*/
public DHGexParameters(int pref_group_len)
{
if ((pref_group_len < MIN_ALLOWED) || (pref_group_len > MAX_ALLOWED))
throw new IllegalArgumentException("pref_group_len out of range!");
this.pref_group_len = pref_group_len;
this.min_group_len = 0;
this.max_group_len = 0;
}
/**
* This constructor can be used to force the sending of a
* <code>SSH_MSG_KEX_DH_GEX_REQUEST</code> request.
* <p>
* Note: older OpenSSH servers don't understand this request, in which
* case you should use the {@link #DHGexParameters(int)} constructor.
* <p>
* All values have to be >= 1024 and <= 8192. Furthermore,
* min_group_len <= pref_group_len <= max_group_len.
*
* @param min_group_len
* @param pref_group_len
* @param max_group_len
*/
public DHGexParameters(int min_group_len, int pref_group_len, int max_group_len)
{
if ((min_group_len < MIN_ALLOWED) || (min_group_len > MAX_ALLOWED))
throw new IllegalArgumentException("min_group_len out of range!");
if ((pref_group_len < MIN_ALLOWED) || (pref_group_len > MAX_ALLOWED))
throw new IllegalArgumentException("pref_group_len out of range!");
if ((max_group_len < MIN_ALLOWED) || (max_group_len > MAX_ALLOWED))
throw new IllegalArgumentException("max_group_len out of range!");
if ((pref_group_len < min_group_len) || (pref_group_len > max_group_len))
throw new IllegalArgumentException("pref_group_len is incompatible with min and max!");
if (max_group_len < min_group_len)
throw new IllegalArgumentException("max_group_len must not be smaller than min_group_len!");
this.min_group_len = min_group_len;
this.pref_group_len = pref_group_len;
this.max_group_len = max_group_len;
}
/**
* Get the maximum group length.
*
* @return the maximum group length, may be <code>zero</code> if
* SSH_MSG_KEX_DH_GEX_REQUEST_OLD should be requested
*/
public int getMax_group_len()
{
return max_group_len;
}
/**
* Get the minimum group length.
*
* @return minimum group length, may be <code>zero</code> if
* SSH_MSG_KEX_DH_GEX_REQUEST_OLD should be requested
*/
public int getMin_group_len()
{
return min_group_len;
}
/**
* Get the preferred group length.
*
* @return the preferred group length
*/
public int getPref_group_len()
{
return pref_group_len;
}
}
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