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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 const unsigned char P[] = { |
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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 const 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 | struct dh_ctx { |
37 | Bignum x, e, p, q, qmask, g; |
38 | }; |
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39 | |
40 | /* |
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41 | * Common DH initialisation. |
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42 | */ |
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43 | static void dh_init(struct dh_ctx *ctx) |
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44 | { |
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45 | ctx->q = bignum_rshift(ctx->p, 1); |
46 | ctx->qmask = bignum_bitmask(ctx->q); |
47 | ctx->x = ctx->e = NULL; |
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48 | } |
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49 | |
50 | /* |
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51 | * Initialise DH for the standard group1. |
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52 | */ |
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53 | void *dh_setup_group1(void) |
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54 | { |
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55 | struct dh_ctx *ctx = snew(struct dh_ctx); |
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56 | ctx->p = bignum_from_bytes(P, sizeof(P)); |
57 | ctx->g = bignum_from_bytes(G, sizeof(G)); |
58 | dh_init(ctx); |
59 | return ctx; |
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60 | } |
61 | |
62 | /* |
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63 | * Initialise DH for an alternative group. |
64 | */ |
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65 | void *dh_setup_group(Bignum pval, Bignum gval) |
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66 | { |
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67 | struct dh_ctx *ctx = snew(struct dh_ctx); |
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68 | ctx->p = copybn(pval); |
69 | ctx->g = copybn(gval); |
70 | dh_init(ctx); |
71 | return ctx; |
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72 | } |
73 | |
74 | /* |
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75 | * Clean up and free a context. |
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76 | */ |
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77 | void dh_cleanup(void *handle) |
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78 | { |
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79 | struct dh_ctx *ctx = (struct dh_ctx *)handle; |
80 | freebn(ctx->x); |
81 | freebn(ctx->e); |
82 | freebn(ctx->p); |
83 | freebn(ctx->g); |
84 | freebn(ctx->q); |
85 | freebn(ctx->qmask); |
86 | sfree(ctx); |
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87 | } |
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88 | |
89 | /* |
90 | * DH stage 1: invent a number x between 1 and q, and compute e = |
91 | * g^x mod p. Return e. |
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92 | * |
93 | * If `nbits' is greater than zero, it is used as an upper limit |
94 | * for the number of bits in x. This is safe provided that (a) you |
95 | * use twice as many bits in x as the number of bits you expect to |
96 | * use in your session key, and (b) the DH group is a safe prime |
97 | * (which SSH demands that it must be). |
98 | * |
99 | * P. C. van Oorschot, M. J. Wiener |
100 | * "On Diffie-Hellman Key Agreement with Short Exponents". |
101 | * Advances in Cryptology: Proceedings of Eurocrypt '96 |
102 | * Springer-Verlag, May 1996. |
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103 | */ |
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104 | Bignum dh_create_e(void *handle, int nbits) |
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105 | { |
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106 | struct dh_ctx *ctx = (struct dh_ctx *)handle; |
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107 | int i; |
108 | |
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109 | int nbytes; |
110 | unsigned char *buf; |
111 | |
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112 | nbytes = ssh1_bignum_length(ctx->qmask); |
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113 | buf = snewn(nbytes, unsigned char); |
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114 | |
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115 | do { |
116 | /* |
117 | * Create a potential x, by ANDing a string of random bytes |
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118 | * with qmask. |
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119 | */ |
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120 | if (ctx->x) |
121 | freebn(ctx->x); |
122 | if (nbits == 0 || nbits > bignum_bitcount(ctx->qmask)) { |
123 | ssh1_write_bignum(buf, ctx->qmask); |
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124 | for (i = 2; i < nbytes; i++) |
125 | buf[i] &= random_byte(); |
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126 | ssh1_read_bignum(buf, nbytes, &ctx->x); /* can't fail */ |
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127 | } else { |
128 | int b, nb; |
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129 | ctx->x = bn_power_2(nbits); |
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130 | b = nb = 0; |
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131 | for (i = 0; i < nbits; i++) { |
132 | if (nb == 0) { |
133 | nb = 8; |
134 | b = random_byte(); |
135 | } |
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136 | bignum_set_bit(ctx->x, i, b & 1); |
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137 | b >>= 1; |
138 | nb--; |
139 | } |
140 | } |
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141 | } while (bignum_cmp(ctx->x, One) <= 0 || bignum_cmp(ctx->x, ctx->q) >= 0); |
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142 | |
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143 | sfree(buf); |
144 | |
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145 | /* |
146 | * Done. Now compute e = g^x mod p. |
147 | */ |
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148 | ctx->e = modpow(ctx->g, ctx->x, ctx->p); |
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149 | |
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150 | return ctx->e; |
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151 | } |
152 | |
153 | /* |
154 | * DH stage 2: given a number f, compute K = f^x mod p. |
155 | */ |
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156 | Bignum dh_find_K(void *handle, Bignum f) |
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157 | { |
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158 | struct dh_ctx *ctx = (struct dh_ctx *)handle; |
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159 | Bignum ret; |
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160 | ret = modpow(f, ctx->x, ctx->p); |
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161 | return ret; |
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162 | } |