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1 | #include "ssh.h" |
2 | |
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3 | const struct ssh_kex ssh_diffiehellman = { |
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4 | "diffie-hellman-group1-sha1" |
5 | }; |
6 | |
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7 | const struct ssh_kex ssh_diffiehellman_gex = { |
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8 | "diffie-hellman-group-exchange-sha1" |
9 | }; |
10 | |
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11 | /* |
12 | * The prime p used in the key exchange. |
13 | */ |
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14 | static unsigned char P[] = { |
15 | 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xC9, 0x0F, 0xDA, 0xA2, |
16 | 0x21, 0x68, 0xC2, 0x34, 0xC4, 0xC6, 0x62, 0x8B, 0x80, 0xDC, 0x1C, 0xD1, |
17 | 0x29, 0x02, 0x4E, 0x08, 0x8A, 0x67, 0xCC, 0x74, 0x02, 0x0B, 0xBE, 0xA6, |
18 | 0x3B, 0x13, 0x9B, 0x22, 0x51, 0x4A, 0x08, 0x79, 0x8E, 0x34, 0x04, 0xDD, |
19 | 0xEF, 0x95, 0x19, 0xB3, 0xCD, 0x3A, 0x43, 0x1B, 0x30, 0x2B, 0x0A, 0x6D, |
20 | 0xF2, 0x5F, 0x14, 0x37, 0x4F, 0xE1, 0x35, 0x6D, 0x6D, 0x51, 0xC2, 0x45, |
21 | 0xE4, 0x85, 0xB5, 0x76, 0x62, 0x5E, 0x7E, 0xC6, 0xF4, 0x4C, 0x42, 0xE9, |
22 | 0xA6, 0x37, 0xED, 0x6B, 0x0B, 0xFF, 0x5C, 0xB6, 0xF4, 0x06, 0xB7, 0xED, |
23 | 0xEE, 0x38, 0x6B, 0xFB, 0x5A, 0x89, 0x9F, 0xA5, 0xAE, 0x9F, 0x24, 0x11, |
24 | 0x7C, 0x4B, 0x1F, 0xE6, 0x49, 0x28, 0x66, 0x51, 0xEC, 0xE6, 0x53, 0x81, |
25 | 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF |
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26 | }; |
27 | |
28 | /* |
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29 | * The generator g = 2. |
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30 | */ |
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31 | static unsigned char G[] = { 2 }; |
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32 | |
33 | /* |
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34 | * Variables. |
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35 | */ |
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36 | static Bignum x, e, p, q, qmask, g; |
37 | static int need_to_free_pg; |
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38 | |
39 | /* |
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40 | * Common DH initialisation. |
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41 | */ |
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42 | static void dh_init(void) |
43 | { |
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44 | q = bignum_rshift(p, 1); |
45 | qmask = bignum_bitmask(q); |
46 | } |
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47 | |
48 | /* |
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49 | * Initialise DH for the standard group1. |
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50 | */ |
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51 | void dh_setup_group1(void) |
52 | { |
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53 | p = bignum_from_bytes(P, sizeof(P)); |
54 | g = bignum_from_bytes(G, sizeof(G)); |
55 | dh_init(); |
56 | } |
57 | |
58 | /* |
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59 | * Initialise DH for an alternative group. |
60 | */ |
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61 | void dh_setup_group(Bignum pval, Bignum gval) |
62 | { |
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63 | p = copybn(pval); |
64 | g = copybn(gval); |
65 | dh_init(); |
66 | } |
67 | |
68 | /* |
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69 | * Clean up. |
70 | */ |
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71 | void dh_cleanup(void) |
72 | { |
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73 | freebn(p); |
74 | freebn(g); |
75 | freebn(q); |
76 | freebn(qmask); |
77 | } |
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78 | |
79 | /* |
80 | * DH stage 1: invent a number x between 1 and q, and compute e = |
81 | * g^x mod p. Return e. |
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82 | * |
83 | * If `nbits' is greater than zero, it is used as an upper limit |
84 | * for the number of bits in x. This is safe provided that (a) you |
85 | * use twice as many bits in x as the number of bits you expect to |
86 | * use in your session key, and (b) the DH group is a safe prime |
87 | * (which SSH demands that it must be). |
88 | * |
89 | * P. C. van Oorschot, M. J. Wiener |
90 | * "On Diffie-Hellman Key Agreement with Short Exponents". |
91 | * Advances in Cryptology: Proceedings of Eurocrypt '96 |
92 | * Springer-Verlag, May 1996. |
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93 | */ |
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94 | Bignum dh_create_e(int nbits) |
95 | { |
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96 | int i; |
97 | |
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98 | int nbytes; |
99 | unsigned char *buf; |
100 | |
101 | nbytes = ssh1_bignum_length(qmask); |
102 | buf = smalloc(nbytes); |
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103 | |
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104 | do { |
105 | /* |
106 | * Create a potential x, by ANDing a string of random bytes |
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107 | * with qmask. |
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108 | */ |
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109 | if (x) |
110 | freebn(x); |
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111 | if (nbits == 0 || nbits > bignum_bitcount(qmask)) { |
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112 | ssh1_write_bignum(buf, qmask); |
113 | for (i = 2; i < nbytes; i++) |
114 | buf[i] &= random_byte(); |
115 | ssh1_read_bignum(buf, &x); |
116 | } else { |
117 | int b, nb; |
118 | x = bn_power_2(nbits); |
119 | nb = 0; |
120 | for (i = 0; i < nbits; i++) { |
121 | if (nb == 0) { |
122 | nb = 8; |
123 | b = random_byte(); |
124 | } |
125 | bignum_set_bit(x, i, b & 1); |
126 | b >>= 1; |
127 | nb--; |
128 | } |
129 | } |
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130 | } while (bignum_cmp(x, One) <= 0 || bignum_cmp(x, q) >= 0); |
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131 | |
132 | /* |
133 | * Done. Now compute e = g^x mod p. |
134 | */ |
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135 | e = modpow(g, x, p); |
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136 | |
137 | return e; |
138 | } |
139 | |
140 | /* |
141 | * DH stage 2: given a number f, compute K = f^x mod p. |
142 | */ |
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143 | Bignum dh_find_K(Bignum f) |
144 | { |
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145 | Bignum ret; |
146 | ret = modpow(f, x, p); |
147 | return ret; |
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148 | } |