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1
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2 package com.trilead.ssh2.crypto.dh;
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3
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4 import java.math.BigInteger;
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5 import java.security.SecureRandom;
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6
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7 import com.trilead.ssh2.DHGexParameters;
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8 import com.trilead.ssh2.crypto.digest.HashForSSH2Types;
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9
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10
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11 /**
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12 * DhGroupExchange.
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13 *
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14 * @author Christian Plattner, plattner@trilead.com
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15 * @version $Id: DhGroupExchange.java,v 1.1 2007/10/15 12:49:57 cplattne Exp $
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16 */
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17 public class DhGroupExchange {
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18 /* Given by the standard */
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19
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20 private BigInteger p;
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21 private BigInteger g;
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22
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23 /* Client public and private */
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24
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25 private BigInteger e;
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26 private BigInteger x;
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27
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28 /* Server public */
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29
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30 private BigInteger f;
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31
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32 /* Shared secret */
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33
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34 private BigInteger k;
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35
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36 public DhGroupExchange(BigInteger p, BigInteger g) {
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37 this.p = p;
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38 this.g = g;
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39 }
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40
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41 public void init(SecureRandom rnd) {
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42 k = null;
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43 x = new BigInteger(p.bitLength() - 1, rnd);
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44 e = g.modPow(x, p);
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45 }
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46
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47 /**
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48 * @return Returns the e.
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49 */
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50 public BigInteger getE() {
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51 if (e == null)
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52 throw new IllegalStateException("Not initialized!");
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53
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54 return e;
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55 }
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56
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57 /**
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58 * @return Returns the shared secret k.
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59 */
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60 public BigInteger getK() {
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61 if (k == null)
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62 throw new IllegalStateException("Shared secret not yet known, need f first!");
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63
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64 return k;
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65 }
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66
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67 /**
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68 * Sets f and calculates the shared secret.
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69 */
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70 public void setF(BigInteger f) {
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71 if (e == null)
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72 throw new IllegalStateException("Not initialized!");
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73
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74 BigInteger zero = BigInteger.valueOf(0);
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75
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76 if (zero.compareTo(f) >= 0 || p.compareTo(f) <= 0)
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77 throw new IllegalArgumentException("Invalid f specified!");
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78
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79 this.f = f;
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80 this.k = f.modPow(x, p);
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81 }
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82
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83 public byte[] calculateH(String hashAlgo, byte[] clientversion, byte[] serverversion,
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84 byte[] clientKexPayload, byte[] serverKexPayload, byte[] hostKey, DHGexParameters para) {
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85 HashForSSH2Types hash = new HashForSSH2Types(hashAlgo);
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86 hash.updateByteString(clientversion);
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87 hash.updateByteString(serverversion);
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88 hash.updateByteString(clientKexPayload);
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89 hash.updateByteString(serverKexPayload);
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90 hash.updateByteString(hostKey);
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91
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92 if (para.getMin_group_len() > 0)
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93 hash.updateUINT32(para.getMin_group_len());
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94
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95 hash.updateUINT32(para.getPref_group_len());
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96
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97 if (para.getMax_group_len() > 0)
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98 hash.updateUINT32(para.getMax_group_len());
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99
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100 hash.updateBigInt(p);
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101 hash.updateBigInt(g);
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102 hash.updateBigInt(e);
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103 hash.updateBigInt(f);
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104 hash.updateBigInt(k);
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105 return hash.getDigest();
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106 }
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107 }
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