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1 | #include <stdio.h> |
2 | #include <stdlib.h> |
3 | |
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4 | #include "ssh.h" |
5 | |
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6 | #define GET_32BIT(cp) \ |
7 | (((unsigned long)(unsigned char)(cp)[0] << 24) | \ |
8 | ((unsigned long)(unsigned char)(cp)[1] << 16) | \ |
9 | ((unsigned long)(unsigned char)(cp)[2] << 8) | \ |
10 | ((unsigned long)(unsigned char)(cp)[3])) |
11 | |
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12 | #define PUT_32BIT(cp, value) { \ |
13 | (cp)[0] = (unsigned char)((value) >> 24); \ |
14 | (cp)[1] = (unsigned char)((value) >> 16); \ |
15 | (cp)[2] = (unsigned char)((value) >> 8); \ |
16 | (cp)[3] = (unsigned char)(value); } |
17 | |
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18 | static void getstring(char **data, int *datalen, char **p, int *length) { |
19 | *p = NULL; |
20 | if (*datalen < 4) |
21 | return; |
22 | *length = GET_32BIT(*data); |
23 | *datalen -= 4; *data += 4; |
24 | if (*datalen < *length) |
25 | return; |
26 | *p = *data; |
27 | *data += *length; *datalen -= *length; |
28 | } |
29 | static Bignum getmp(char **data, int *datalen) { |
30 | char *p; |
31 | int i, j, length; |
32 | Bignum b; |
33 | |
34 | getstring(data, datalen, &p, &length); |
35 | if (!p) |
36 | return NULL; |
37 | if (p[0] & 0x80) |
38 | return NULL; /* negative mp */ |
39 | b = newbn((length+1)/2); |
40 | for (i = 0; i < length; i++) { |
41 | j = length - 1 - i; |
42 | if (j & 1) |
43 | b[j/2+1] |= ((unsigned char)p[i]) << 8; |
44 | else |
45 | b[j/2+1] |= ((unsigned char)p[i]); |
46 | } |
47 | return b; |
48 | } |
49 | |
50 | static Bignum get160(char **data, int *datalen) { |
51 | char *p; |
52 | int i, j, length; |
53 | Bignum b; |
54 | |
55 | p = *data; |
56 | *data += 20; *datalen -= 20; |
57 | |
58 | length = 20; |
59 | while (length > 0 && !p[0]) |
60 | p++, length--; |
61 | b = newbn((length+1)/2); |
62 | for (i = 0; i < length; i++) { |
63 | j = length - 1 - i; |
64 | if (j & 1) |
65 | b[j/2+1] |= ((unsigned char)p[i]) << 8; |
66 | else |
67 | b[j/2+1] |= ((unsigned char)p[i]); |
68 | } |
69 | return b; |
70 | } |
71 | |
72 | static Bignum dss_p, dss_q, dss_g, dss_y; |
73 | |
74 | static void dss_setkey(char *data, int len) { |
75 | char *p; |
76 | int slen; |
77 | getstring(&data, &len, &p, &slen); |
78 | if (!p || memcmp(p, "ssh-dss", 7)) { |
79 | dss_p = NULL; |
80 | return; |
81 | } |
82 | dss_p = getmp(&data, &len); |
83 | dss_q = getmp(&data, &len); |
84 | dss_g = getmp(&data, &len); |
85 | dss_y = getmp(&data, &len); |
86 | } |
87 | |
88 | static char *dss_fmtkey(void) { |
89 | char *p; |
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90 | int len, i, pos, nibbles; |
91 | static const char hex[] = "0123456789abcdef"; |
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92 | if (!dss_p) |
93 | return NULL; |
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94 | len = 8 + 4 + 1; /* 4 x "0x", punctuation, \0 */ |
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95 | len += 4 * (dss_p[0] + dss_q[0] + dss_g[0] + dss_y[0]); /* digits */ |
96 | p = malloc(len); |
97 | if (!p) return NULL; |
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98 | |
99 | pos = 0; |
100 | pos += sprintf(p+pos, "0x"); |
101 | nibbles = (3 + ssh1_bignum_bitcount(dss_p))/4; if (nibbles<1) nibbles=1; |
102 | for (i=nibbles; i-- ;) |
103 | p[pos++] = hex[(bignum_byte(dss_p, i/2) >> (4*(i%2))) & 0xF]; |
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104 | pos += sprintf(p+pos, ",0x"); |
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105 | nibbles = (3 + ssh1_bignum_bitcount(dss_q))/4; if (nibbles<1) nibbles=1; |
106 | for (i=nibbles; i-- ;) |
107 | p[pos++] = hex[(bignum_byte(dss_q, i/2) >> (4*(i%2))) & 0xF]; |
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108 | pos += sprintf(p+pos, ",0x"); |
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109 | nibbles = (3 + ssh1_bignum_bitcount(dss_g))/4; if (nibbles<1) nibbles=1; |
110 | for (i=nibbles; i-- ;) |
111 | p[pos++] = hex[(bignum_byte(dss_g, i/2) >> (4*(i%2))) & 0xF]; |
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112 | pos += sprintf(p+pos, ",0x"); |
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113 | nibbles = (3 + ssh1_bignum_bitcount(dss_y))/4; if (nibbles<1) nibbles=1; |
114 | for (i=nibbles; i-- ;) |
115 | p[pos++] = hex[(bignum_byte(dss_y, i/2) >> (4*(i%2))) & 0xF]; |
116 | p[pos] = '\0'; |
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117 | return p; |
118 | } |
119 | |
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120 | static char *dss_fingerprint(void) { |
121 | struct MD5Context md5c; |
122 | unsigned char digest[16], lenbuf[4]; |
123 | char buffer[16*3+40]; |
124 | char *ret; |
125 | int numlen, i; |
126 | |
127 | MD5Init(&md5c); |
128 | MD5Update(&md5c, "\0\0\0\7ssh-dss", 11); |
129 | |
130 | #define ADD_BIGNUM(bignum) \ |
131 | numlen = (ssh1_bignum_bitcount(bignum)+8)/8; \ |
132 | PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \ |
133 | for (i = numlen; i-- ;) { \ |
134 | unsigned char c = bignum_byte(bignum, i); \ |
135 | MD5Update(&md5c, &c, 1); \ |
136 | } |
137 | ADD_BIGNUM(dss_p); |
138 | ADD_BIGNUM(dss_q); |
139 | ADD_BIGNUM(dss_g); |
140 | ADD_BIGNUM(dss_y); |
141 | #undef ADD_BIGNUM |
142 | |
143 | MD5Final(digest, &md5c); |
144 | |
145 | sprintf(buffer, "%d ", ssh1_bignum_bitcount(dss_p)); |
146 | for (i = 0; i < 16; i++) |
147 | sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]); |
148 | ret = malloc(strlen(buffer)+1); |
149 | if (ret) |
150 | strcpy(ret, buffer); |
151 | return ret; |
152 | } |
153 | |
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154 | static int dss_verifysig(char *sig, int siglen, char *data, int datalen) { |
155 | char *p; |
156 | int i, slen; |
157 | char hash[20]; |
158 | Bignum qm2, r, s, w, i1, i2, i3, u1, u2, sha, v; |
159 | int ret; |
160 | |
161 | if (!dss_p) |
162 | return 0; |
163 | |
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164 | /* |
165 | * Commercial SSH (2.0.13) and OpenSSH disagree over the format |
166 | * of a DSA signature. OpenSSH is in line with the IETF drafts: |
167 | * it uses a string "ssh-dss", followed by a 40-byte string |
168 | * containing two 160-bit integers end-to-end. Commercial SSH |
169 | * can't be bothered with the header bit, and considers a DSA |
170 | * signature blob to be _just_ the 40-byte string containing |
171 | * the two 160-bit integers. We tell them apart by measuring |
172 | * the length: length 40 means the commercial-SSH bug, anything |
173 | * else is assumed to be IETF-compliant. |
174 | */ |
175 | if (siglen != 40) { /* bug not present; read admin fields */ |
176 | getstring(&sig, &siglen, &p, &slen); |
177 | if (!p || memcmp(p, "ssh-dss", 7)) { |
178 | return 0; |
179 | } |
180 | sig += 4, siglen -= 4; /* skip yet another length field */ |
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181 | } |
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182 | r = get160(&sig, &siglen); |
183 | s = get160(&sig, &siglen); |
184 | if (!r || !s) |
185 | return 0; |
186 | |
187 | /* |
188 | * Step 1. w <- s^-1 mod q. |
189 | */ |
190 | w = newbn(dss_q[0]); |
191 | qm2 = copybn(dss_q); |
192 | decbn(qm2); decbn(qm2); |
193 | /* Now qm2 is q-2, and by Fermat's Little Theorem, s^qm2 == s^-1 (mod q). |
194 | * This is a silly way to do it; may fix it later. */ |
195 | modpow(s, qm2, dss_q, w); |
196 | |
197 | /* |
198 | * Step 2. u1 <- SHA(message) * w mod q. |
199 | */ |
200 | u1 = newbn(dss_q[0]); |
201 | SHA_Simple(data, datalen, hash); |
202 | p = hash; slen = 20; sha = get160(&p, &slen); |
203 | modmul(sha, w, dss_q, u1); |
204 | |
205 | /* |
206 | * Step 3. u2 <- r * w mod q. |
207 | */ |
208 | u2 = newbn(dss_q[0]); |
209 | modmul(r, w, dss_q, u2); |
210 | |
211 | /* |
212 | * Step 4. v <- (g^u1 * y^u2 mod p) mod q. |
213 | */ |
214 | i1 = newbn(dss_p[0]); |
215 | i2 = newbn(dss_p[0]); |
216 | i3 = newbn(dss_p[0]); |
217 | v = newbn(dss_q[0]); |
218 | modpow(dss_g, u1, dss_p, i1); |
219 | modpow(dss_y, u2, dss_p, i2); |
220 | modmul(i1, i2, dss_p, i3); |
221 | modmul(i3, One, dss_q, v); |
222 | |
223 | /* |
224 | * Step 5. v should now be equal to r. |
225 | */ |
226 | |
227 | ret = 1; |
228 | for (i = 1; i <= v[0] || i <= r[0]; i++) { |
229 | if ((i > v[0] && r[i] != 0) || |
230 | (i > r[0] && v[i] != 0) || |
231 | (i <= v[0] && i <= r[0] && r[i] != v[i])) |
232 | ret = 0; |
233 | } |
234 | |
235 | freebn(w); |
236 | freebn(qm2); |
237 | freebn(sha); |
238 | freebn(i1); |
239 | freebn(i2); |
240 | freebn(i3); |
241 | freebn(v); |
242 | freebn(r); |
243 | freebn(s); |
244 | |
245 | return ret; |
246 | } |
247 | |
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248 | struct ssh_hostkey ssh_dss = { |
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249 | dss_setkey, |
250 | dss_fmtkey, |
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251 | dss_fingerprint, |
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252 | dss_verifysig, |
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253 | "ssh-dss", |
254 | "dss" |
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255 | }; |