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2 package com.trilead.ssh2;
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3
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4 /**
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5 * A <code>DHGexParameters</code> object can be used to specify parameters for
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6 * the diffie-hellman group exchange.
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7 * <p>
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8 * Depending on which constructor is used, either the use of a
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9 * <code>SSH_MSG_KEX_DH_GEX_REQUEST</code> or <code>SSH_MSG_KEX_DH_GEX_REQUEST_OLD</code>
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10 * can be forced.
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11 *
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12 * @see Connection#setDHGexParameters(DHGexParameters)
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13 * @author Christian Plattner, plattner@trilead.com
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14 * @version $Id: DHGexParameters.java,v 1.1 2007/10/15 12:49:56 cplattne Exp $
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15 */
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16
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17 public class DHGexParameters {
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18 private final int min_group_len;
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19 private final int pref_group_len;
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20 private final int max_group_len;
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21
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22 private static final int MIN_ALLOWED = 1024;
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23 private static final int MAX_ALLOWED = 8192;
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24
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25 /**
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26 * Same as calling {@link #DHGexParameters(int, int, int) DHGexParameters(1024, 1024, 4096)}.
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27 * This is also the default used by the Connection class.
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28 *
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29 */
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30 public DHGexParameters() {
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31 this(1024, 1024, 4096);
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32 }
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33
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34 /**
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35 * This constructor can be used to force the sending of a
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36 * <code>SSH_MSG_KEX_DH_GEX_REQUEST_OLD</code> request.
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37 * Internally, the minimum and maximum group lengths will
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38 * be set to zero.
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39 *
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40 * @param pref_group_len has to be >= 1024 and <= 8192
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41 */
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42 public DHGexParameters(int pref_group_len) {
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43 if ((pref_group_len < MIN_ALLOWED) || (pref_group_len > MAX_ALLOWED))
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44 throw new IllegalArgumentException("pref_group_len out of range!");
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45
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46 this.pref_group_len = pref_group_len;
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47 this.min_group_len = 0;
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48 this.max_group_len = 0;
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49 }
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50
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51 /**
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52 * This constructor can be used to force the sending of a
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53 * <code>SSH_MSG_KEX_DH_GEX_REQUEST</code> request.
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54 * <p>
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55 * Note: older OpenSSH servers don't understand this request, in which
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56 * case you should use the {@link #DHGexParameters(int)} constructor.
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57 * <p>
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58 * All values have to be >= 1024 and <= 8192. Furthermore,
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59 * min_group_len <= pref_group_len <= max_group_len.
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60 *
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61 * @param min_group_len
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62 * @param pref_group_len
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63 * @param max_group_len
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64 */
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65 public DHGexParameters(int min_group_len, int pref_group_len, int max_group_len) {
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66 if ((min_group_len < MIN_ALLOWED) || (min_group_len > MAX_ALLOWED))
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67 throw new IllegalArgumentException("min_group_len out of range!");
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68
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69 if ((pref_group_len < MIN_ALLOWED) || (pref_group_len > MAX_ALLOWED))
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70 throw new IllegalArgumentException("pref_group_len out of range!");
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71
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72 if ((max_group_len < MIN_ALLOWED) || (max_group_len > MAX_ALLOWED))
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73 throw new IllegalArgumentException("max_group_len out of range!");
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74
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75 if ((pref_group_len < min_group_len) || (pref_group_len > max_group_len))
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76 throw new IllegalArgumentException("pref_group_len is incompatible with min and max!");
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77
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78 if (max_group_len < min_group_len)
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79 throw new IllegalArgumentException("max_group_len must not be smaller than min_group_len!");
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80
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81 this.min_group_len = min_group_len;
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82 this.pref_group_len = pref_group_len;
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83 this.max_group_len = max_group_len;
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84 }
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85
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86 /**
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87 * Get the maximum group length.
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88 *
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89 * @return the maximum group length, may be <code>zero</code> if
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90 * SSH_MSG_KEX_DH_GEX_REQUEST_OLD should be requested
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91 */
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92 public int getMax_group_len() {
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93 return max_group_len;
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94 }
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95
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96 /**
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97 * Get the minimum group length.
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98 *
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99 * @return minimum group length, may be <code>zero</code> if
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100 * SSH_MSG_KEX_DH_GEX_REQUEST_OLD should be requested
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101 */
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102 public int getMin_group_len() {
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103 return min_group_len;
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104 }
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105
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106 /**
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107 * Get the preferred group length.
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108 *
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109 * @return the preferred group length
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110 */
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111 public int getPref_group_len() {
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112 return pref_group_len;
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113 }
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114 }
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