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1 | #include <stdio.h> |
2 | #include <stdlib.h> |
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3 | #include <assert.h> |
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4 | |
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5 | #include "ssh.h" |
6 | |
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7 | #define GET_32BIT(cp) \ |
8 | (((unsigned long)(unsigned char)(cp)[0] << 24) | \ |
9 | ((unsigned long)(unsigned char)(cp)[1] << 16) | \ |
10 | ((unsigned long)(unsigned char)(cp)[2] << 8) | \ |
11 | ((unsigned long)(unsigned char)(cp)[3])) |
12 | |
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13 | #define PUT_32BIT(cp, value) { \ |
14 | (cp)[0] = (unsigned char)((value) >> 24); \ |
15 | (cp)[1] = (unsigned char)((value) >> 16); \ |
16 | (cp)[2] = (unsigned char)((value) >> 8); \ |
17 | (cp)[3] = (unsigned char)(value); } |
18 | |
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19 | #if 0 |
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20 | #define DEBUG_DSS |
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21 | #else |
22 | #define diagbn(x,y) |
23 | #endif |
24 | |
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25 | static void getstring(char **data, int *datalen, char **p, int *length) { |
26 | *p = NULL; |
27 | if (*datalen < 4) |
28 | return; |
29 | *length = GET_32BIT(*data); |
30 | *datalen -= 4; *data += 4; |
31 | if (*datalen < *length) |
32 | return; |
33 | *p = *data; |
34 | *data += *length; *datalen -= *length; |
35 | } |
36 | static Bignum getmp(char **data, int *datalen) { |
37 | char *p; |
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38 | int length; |
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39 | Bignum b; |
40 | |
41 | getstring(data, datalen, &p, &length); |
42 | if (!p) |
43 | return NULL; |
44 | if (p[0] & 0x80) |
45 | return NULL; /* negative mp */ |
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46 | b = bignum_from_bytes(p, length); |
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47 | return b; |
48 | } |
49 | |
50 | static Bignum get160(char **data, int *datalen) { |
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51 | Bignum b; |
52 | |
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53 | b = bignum_from_bytes(*data, 20); |
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54 | *data += 20; *datalen -= 20; |
55 | |
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56 | return b; |
57 | } |
58 | |
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59 | struct dss_key { |
60 | Bignum p, q, g, y; |
61 | }; |
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62 | |
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63 | static void *dss_newkey(char *data, int len) { |
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64 | char *p; |
65 | int slen; |
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66 | struct dss_key *dss; |
67 | |
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68 | dss = smalloc(sizeof(struct dss_key)); |
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69 | if (!dss) return NULL; |
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70 | getstring(&data, &len, &p, &slen); |
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71 | |
72 | #ifdef DEBUG_DSS |
73 | { |
74 | int i; |
75 | printf("key:"); |
76 | for (i=0;i<len;i++) |
77 | printf(" %02x", (unsigned char)(data[i])); |
78 | printf("\n"); |
79 | } |
80 | #endif |
81 | |
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82 | if (!p || memcmp(p, "ssh-dss", 7)) { |
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83 | sfree(dss); |
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84 | return NULL; |
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85 | } |
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86 | dss->p = getmp(&data, &len); |
87 | dss->q = getmp(&data, &len); |
88 | dss->g = getmp(&data, &len); |
89 | dss->y = getmp(&data, &len); |
90 | |
91 | return dss; |
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92 | } |
93 | |
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94 | static void dss_freekey(void *key) { |
95 | struct dss_key *dss = (struct dss_key *)key; |
96 | freebn(dss->p); |
97 | freebn(dss->q); |
98 | freebn(dss->g); |
99 | freebn(dss->y); |
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100 | sfree(dss); |
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101 | } |
102 | |
103 | static char *dss_fmtkey(void *key) { |
104 | struct dss_key *dss = (struct dss_key *)key; |
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105 | char *p; |
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106 | int len, i, pos, nibbles; |
107 | static const char hex[] = "0123456789abcdef"; |
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108 | if (!dss->p) |
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109 | return NULL; |
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110 | len = 8 + 4 + 1; /* 4 x "0x", punctuation, \0 */ |
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111 | len += 4 * (ssh1_bignum_bitcount(dss->p)+15)/16; |
112 | len += 4 * (ssh1_bignum_bitcount(dss->q)+15)/16; |
113 | len += 4 * (ssh1_bignum_bitcount(dss->g)+15)/16; |
114 | len += 4 * (ssh1_bignum_bitcount(dss->y)+15)/16; |
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115 | p = smalloc(len); |
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116 | if (!p) return NULL; |
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117 | |
118 | pos = 0; |
119 | pos += sprintf(p+pos, "0x"); |
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120 | nibbles = (3 + ssh1_bignum_bitcount(dss->p))/4; if (nibbles<1) nibbles=1; |
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121 | for (i=nibbles; i-- ;) |
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122 | p[pos++] = hex[(bignum_byte(dss->p, i/2) >> (4*(i%2))) & 0xF]; |
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123 | pos += sprintf(p+pos, ",0x"); |
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124 | nibbles = (3 + ssh1_bignum_bitcount(dss->q))/4; if (nibbles<1) nibbles=1; |
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125 | for (i=nibbles; i-- ;) |
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126 | p[pos++] = hex[(bignum_byte(dss->q, i/2) >> (4*(i%2))) & 0xF]; |
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127 | pos += sprintf(p+pos, ",0x"); |
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128 | nibbles = (3 + ssh1_bignum_bitcount(dss->g))/4; if (nibbles<1) nibbles=1; |
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129 | for (i=nibbles; i-- ;) |
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130 | p[pos++] = hex[(bignum_byte(dss->g, i/2) >> (4*(i%2))) & 0xF]; |
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131 | pos += sprintf(p+pos, ",0x"); |
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132 | nibbles = (3 + ssh1_bignum_bitcount(dss->y))/4; if (nibbles<1) nibbles=1; |
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133 | for (i=nibbles; i-- ;) |
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134 | p[pos++] = hex[(bignum_byte(dss->y, i/2) >> (4*(i%2))) & 0xF]; |
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135 | p[pos] = '\0'; |
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136 | return p; |
137 | } |
138 | |
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139 | static char *dss_fingerprint(void *key) { |
140 | struct dss_key *dss = (struct dss_key *)key; |
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141 | struct MD5Context md5c; |
142 | unsigned char digest[16], lenbuf[4]; |
143 | char buffer[16*3+40]; |
144 | char *ret; |
145 | int numlen, i; |
146 | |
147 | MD5Init(&md5c); |
148 | MD5Update(&md5c, "\0\0\0\7ssh-dss", 11); |
149 | |
150 | #define ADD_BIGNUM(bignum) \ |
151 | numlen = (ssh1_bignum_bitcount(bignum)+8)/8; \ |
152 | PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \ |
153 | for (i = numlen; i-- ;) { \ |
154 | unsigned char c = bignum_byte(bignum, i); \ |
155 | MD5Update(&md5c, &c, 1); \ |
156 | } |
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157 | ADD_BIGNUM(dss->p); |
158 | ADD_BIGNUM(dss->q); |
159 | ADD_BIGNUM(dss->g); |
160 | ADD_BIGNUM(dss->y); |
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161 | #undef ADD_BIGNUM |
162 | |
163 | MD5Final(digest, &md5c); |
164 | |
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165 | sprintf(buffer, "ssh-dss %d ", ssh1_bignum_bitcount(dss->p)); |
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166 | for (i = 0; i < 16; i++) |
167 | sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]); |
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168 | ret = smalloc(strlen(buffer)+1); |
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169 | if (ret) |
170 | strcpy(ret, buffer); |
171 | return ret; |
172 | } |
173 | |
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174 | static int dss_verifysig(void *key, char *sig, int siglen, |
175 | char *data, int datalen) { |
176 | struct dss_key *dss = (struct dss_key *)key; |
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177 | char *p; |
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178 | int slen; |
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179 | char hash[20]; |
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180 | Bignum r, s, w, gu1p, yu2p, gu1yu2p, u1, u2, sha, v; |
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181 | int ret; |
182 | |
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183 | if (!dss->p) |
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184 | return 0; |
185 | |
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186 | #ifdef DEBUG_DSS |
187 | { |
188 | int i; |
189 | printf("sig:"); |
190 | for (i=0;i<siglen;i++) |
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191 | printf(" %02x", (unsigned char)(sig[i])); |
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192 | printf("\n"); |
193 | } |
194 | #endif |
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195 | /* |
196 | * Commercial SSH (2.0.13) and OpenSSH disagree over the format |
197 | * of a DSA signature. OpenSSH is in line with the IETF drafts: |
198 | * it uses a string "ssh-dss", followed by a 40-byte string |
199 | * containing two 160-bit integers end-to-end. Commercial SSH |
200 | * can't be bothered with the header bit, and considers a DSA |
201 | * signature blob to be _just_ the 40-byte string containing |
202 | * the two 160-bit integers. We tell them apart by measuring |
203 | * the length: length 40 means the commercial-SSH bug, anything |
204 | * else is assumed to be IETF-compliant. |
205 | */ |
206 | if (siglen != 40) { /* bug not present; read admin fields */ |
207 | getstring(&sig, &siglen, &p, &slen); |
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208 | if (!p || slen != 7 || memcmp(p, "ssh-dss", 7)) { |
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209 | return 0; |
210 | } |
211 | sig += 4, siglen -= 4; /* skip yet another length field */ |
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212 | } |
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213 | diagbn("p=", dss->p); |
214 | diagbn("q=", dss->q); |
215 | diagbn("g=", dss->g); |
216 | diagbn("y=", dss->y); |
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217 | r = get160(&sig, &siglen); |
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218 | diagbn("r=", r); |
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219 | s = get160(&sig, &siglen); |
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220 | diagbn("s=", s); |
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221 | if (!r || !s) |
222 | return 0; |
223 | |
224 | /* |
225 | * Step 1. w <- s^-1 mod q. |
226 | */ |
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227 | w = modinv(s, dss->q); |
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228 | diagbn("w=", w); |
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229 | |
230 | /* |
231 | * Step 2. u1 <- SHA(message) * w mod q. |
232 | */ |
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233 | SHA_Simple(data, datalen, hash); |
234 | p = hash; slen = 20; sha = get160(&p, &slen); |
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235 | diagbn("sha=", sha); |
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236 | u1 = modmul(sha, w, dss->q); |
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237 | diagbn("u1=", u1); |
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238 | |
239 | /* |
240 | * Step 3. u2 <- r * w mod q. |
241 | */ |
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242 | u2 = modmul(r, w, dss->q); |
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243 | diagbn("u2=", u2); |
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244 | |
245 | /* |
246 | * Step 4. v <- (g^u1 * y^u2 mod p) mod q. |
247 | */ |
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248 | gu1p = modpow(dss->g, u1, dss->p); |
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249 | diagbn("gu1p=", gu1p); |
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250 | yu2p = modpow(dss->y, u2, dss->p); |
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251 | diagbn("yu2p=", yu2p); |
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252 | gu1yu2p = modmul(gu1p, yu2p, dss->p); |
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253 | diagbn("gu1yu2p=", gu1yu2p); |
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254 | v = modmul(gu1yu2p, One, dss->q); |
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255 | diagbn("gu1yu2q=v=", v); |
256 | diagbn("r=", r); |
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257 | |
258 | /* |
259 | * Step 5. v should now be equal to r. |
260 | */ |
261 | |
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262 | ret = !bignum_cmp(v, r); |
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263 | |
264 | freebn(w); |
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265 | freebn(sha); |
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266 | freebn(gu1p); |
267 | freebn(yu2p); |
268 | freebn(gu1yu2p); |
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269 | freebn(v); |
270 | freebn(r); |
271 | freebn(s); |
272 | |
273 | return ret; |
274 | } |
275 | |
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276 | static unsigned char *dss_public_blob(void *key, int *len) { |
277 | struct dss_key *dss = (struct dss_key *)key; |
278 | int plen, qlen, glen, ylen, bloblen; |
279 | int i; |
280 | unsigned char *blob, *p; |
281 | |
282 | plen = (ssh1_bignum_bitcount(dss->p)+8)/8; |
283 | qlen = (ssh1_bignum_bitcount(dss->q)+8)/8; |
284 | glen = (ssh1_bignum_bitcount(dss->g)+8)/8; |
285 | ylen = (ssh1_bignum_bitcount(dss->y)+8)/8; |
286 | |
287 | /* |
288 | * string "ssh-dss", mpint p, mpint q, mpint g, mpint y. Total |
289 | * 27 + sum of lengths. (five length fields, 20+7=27). |
290 | */ |
291 | bloblen = 27+plen+qlen+glen+ylen; |
292 | blob = smalloc(bloblen); |
293 | p = blob; |
294 | PUT_32BIT(p, 7); p += 4; |
295 | memcpy(p, "ssh-dss", 7); p += 7; |
296 | PUT_32BIT(p, plen); p += 4; |
297 | for (i = plen; i-- ;) *p++ = bignum_byte(dss->p, i); |
298 | PUT_32BIT(p, qlen); p += 4; |
299 | for (i = qlen; i-- ;) *p++ = bignum_byte(dss->q, i); |
300 | PUT_32BIT(p, glen); p += 4; |
301 | for (i = glen; i-- ;) *p++ = bignum_byte(dss->g, i); |
302 | PUT_32BIT(p, ylen); p += 4; |
303 | for (i = ylen; i-- ;) *p++ = bignum_byte(dss->y, i); |
304 | assert(p == blob + bloblen); |
305 | *len = bloblen; |
306 | return blob; |
307 | } |
308 | |
309 | static unsigned char *dss_private_blob(void *key, int *len) { |
310 | return NULL; /* can't handle DSS private keys */ |
311 | } |
312 | |
313 | static void *dss_createkey(unsigned char *pub_blob, int pub_len, |
314 | unsigned char *priv_blob, int priv_len) { |
315 | return NULL; /* can't handle DSS private keys */ |
316 | } |
317 | |
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318 | static void *dss_openssh_createkey(unsigned char **blob, int *len) { |
319 | return NULL; /* can't handle DSS private keys */ |
320 | } |
321 | |
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322 | unsigned char *dss_sign(void *key, char *data, int datalen, int *siglen) { |
323 | return NULL; /* can't handle DSS private keys */ |
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324 | } |
325 | |
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326 | const struct ssh_signkey ssh_dss = { |
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327 | dss_newkey, |
328 | dss_freekey, |
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329 | dss_fmtkey, |
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330 | dss_public_blob, |
331 | dss_private_blob, |
332 | dss_createkey, |
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333 | dss_openssh_createkey, |
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334 | dss_fingerprint, |
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335 | dss_verifysig, |
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336 | dss_sign, |
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337 | "ssh-dss", |
338 | "dss" |
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339 | }; |