7cca0d81 |
1 | #include <stdio.h> |
2 | #include <stdlib.h> |
3 | |
e5574168 |
4 | #include "ssh.h" |
5 | |
7cca0d81 |
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 | |
d5859615 |
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 | |
9c621433 |
18 | #if 0 |
c5fbd713 |
19 | #define DEBUG_DSS |
9c621433 |
20 | #else |
21 | #define diagbn(x,y) |
22 | #endif |
23 | |
7cca0d81 |
24 | static void getstring(char **data, int *datalen, char **p, int *length) { |
25 | *p = NULL; |
26 | if (*datalen < 4) |
27 | return; |
28 | *length = GET_32BIT(*data); |
29 | *datalen -= 4; *data += 4; |
30 | if (*datalen < *length) |
31 | return; |
32 | *p = *data; |
33 | *data += *length; *datalen -= *length; |
34 | } |
35 | static Bignum getmp(char **data, int *datalen) { |
36 | char *p; |
3709bfe9 |
37 | int length; |
7cca0d81 |
38 | Bignum b; |
39 | |
40 | getstring(data, datalen, &p, &length); |
41 | if (!p) |
42 | return NULL; |
43 | if (p[0] & 0x80) |
44 | return NULL; /* negative mp */ |
3709bfe9 |
45 | b = bignum_from_bytes(p, length); |
7cca0d81 |
46 | return b; |
47 | } |
48 | |
49 | static Bignum get160(char **data, int *datalen) { |
7cca0d81 |
50 | Bignum b; |
51 | |
3709bfe9 |
52 | b = bignum_from_bytes(*data, 20); |
7cca0d81 |
53 | *data += 20; *datalen -= 20; |
54 | |
7cca0d81 |
55 | return b; |
56 | } |
57 | |
e055a386 |
58 | struct dss_key { |
59 | Bignum p, q, g, y; |
60 | }; |
7cca0d81 |
61 | |
e055a386 |
62 | static void *dss_newkey(char *data, int len) { |
7cca0d81 |
63 | char *p; |
64 | int slen; |
e055a386 |
65 | struct dss_key *dss; |
66 | |
dcbde236 |
67 | dss = smalloc(sizeof(struct dss_key)); |
e055a386 |
68 | if (!dss) return NULL; |
7cca0d81 |
69 | getstring(&data, &len, &p, &slen); |
9c621433 |
70 | |
71 | #ifdef DEBUG_DSS |
72 | { |
73 | int i; |
74 | printf("key:"); |
75 | for (i=0;i<len;i++) |
76 | printf(" %02x", (unsigned char)(data[i])); |
77 | printf("\n"); |
78 | } |
79 | #endif |
80 | |
7cca0d81 |
81 | if (!p || memcmp(p, "ssh-dss", 7)) { |
dcbde236 |
82 | sfree(dss); |
e055a386 |
83 | return NULL; |
7cca0d81 |
84 | } |
e055a386 |
85 | dss->p = getmp(&data, &len); |
86 | dss->q = getmp(&data, &len); |
87 | dss->g = getmp(&data, &len); |
88 | dss->y = getmp(&data, &len); |
89 | |
90 | return dss; |
7cca0d81 |
91 | } |
92 | |
e055a386 |
93 | static void dss_freekey(void *key) { |
94 | struct dss_key *dss = (struct dss_key *)key; |
95 | freebn(dss->p); |
96 | freebn(dss->q); |
97 | freebn(dss->g); |
98 | freebn(dss->y); |
dcbde236 |
99 | sfree(dss); |
e055a386 |
100 | } |
101 | |
102 | static char *dss_fmtkey(void *key) { |
103 | struct dss_key *dss = (struct dss_key *)key; |
7cca0d81 |
104 | char *p; |
d5859615 |
105 | int len, i, pos, nibbles; |
106 | static const char hex[] = "0123456789abcdef"; |
e055a386 |
107 | if (!dss->p) |
7cca0d81 |
108 | return NULL; |
d5859615 |
109 | len = 8 + 4 + 1; /* 4 x "0x", punctuation, \0 */ |
3709bfe9 |
110 | len += 4 * (ssh1_bignum_bitcount(dss->p)+15)/16; |
111 | len += 4 * (ssh1_bignum_bitcount(dss->q)+15)/16; |
112 | len += 4 * (ssh1_bignum_bitcount(dss->g)+15)/16; |
113 | len += 4 * (ssh1_bignum_bitcount(dss->y)+15)/16; |
dcbde236 |
114 | p = smalloc(len); |
7cca0d81 |
115 | if (!p) return NULL; |
d5859615 |
116 | |
117 | pos = 0; |
118 | pos += sprintf(p+pos, "0x"); |
e055a386 |
119 | nibbles = (3 + ssh1_bignum_bitcount(dss->p))/4; if (nibbles<1) nibbles=1; |
d5859615 |
120 | for (i=nibbles; i-- ;) |
e055a386 |
121 | p[pos++] = hex[(bignum_byte(dss->p, i/2) >> (4*(i%2))) & 0xF]; |
3aa0b691 |
122 | pos += sprintf(p+pos, ",0x"); |
e055a386 |
123 | nibbles = (3 + ssh1_bignum_bitcount(dss->q))/4; if (nibbles<1) nibbles=1; |
d5859615 |
124 | for (i=nibbles; i-- ;) |
e055a386 |
125 | p[pos++] = hex[(bignum_byte(dss->q, i/2) >> (4*(i%2))) & 0xF]; |
3aa0b691 |
126 | pos += sprintf(p+pos, ",0x"); |
e055a386 |
127 | nibbles = (3 + ssh1_bignum_bitcount(dss->g))/4; if (nibbles<1) nibbles=1; |
d5859615 |
128 | for (i=nibbles; i-- ;) |
e055a386 |
129 | p[pos++] = hex[(bignum_byte(dss->g, i/2) >> (4*(i%2))) & 0xF]; |
3aa0b691 |
130 | pos += sprintf(p+pos, ",0x"); |
e055a386 |
131 | nibbles = (3 + ssh1_bignum_bitcount(dss->y))/4; if (nibbles<1) nibbles=1; |
d5859615 |
132 | for (i=nibbles; i-- ;) |
e055a386 |
133 | p[pos++] = hex[(bignum_byte(dss->y, i/2) >> (4*(i%2))) & 0xF]; |
d5859615 |
134 | p[pos] = '\0'; |
7cca0d81 |
135 | return p; |
136 | } |
137 | |
e055a386 |
138 | static char *dss_fingerprint(void *key) { |
139 | struct dss_key *dss = (struct dss_key *)key; |
d5859615 |
140 | struct MD5Context md5c; |
141 | unsigned char digest[16], lenbuf[4]; |
142 | char buffer[16*3+40]; |
143 | char *ret; |
144 | int numlen, i; |
145 | |
146 | MD5Init(&md5c); |
147 | MD5Update(&md5c, "\0\0\0\7ssh-dss", 11); |
148 | |
149 | #define ADD_BIGNUM(bignum) \ |
150 | numlen = (ssh1_bignum_bitcount(bignum)+8)/8; \ |
151 | PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \ |
152 | for (i = numlen; i-- ;) { \ |
153 | unsigned char c = bignum_byte(bignum, i); \ |
154 | MD5Update(&md5c, &c, 1); \ |
155 | } |
e055a386 |
156 | ADD_BIGNUM(dss->p); |
157 | ADD_BIGNUM(dss->q); |
158 | ADD_BIGNUM(dss->g); |
159 | ADD_BIGNUM(dss->y); |
d5859615 |
160 | #undef ADD_BIGNUM |
161 | |
162 | MD5Final(digest, &md5c); |
163 | |
e055a386 |
164 | sprintf(buffer, "%d ", ssh1_bignum_bitcount(dss->p)); |
d5859615 |
165 | for (i = 0; i < 16; i++) |
166 | sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]); |
dcbde236 |
167 | ret = smalloc(strlen(buffer)+1); |
d5859615 |
168 | if (ret) |
169 | strcpy(ret, buffer); |
170 | return ret; |
171 | } |
172 | |
e055a386 |
173 | static int dss_verifysig(void *key, char *sig, int siglen, |
174 | char *data, int datalen) { |
175 | struct dss_key *dss = (struct dss_key *)key; |
7cca0d81 |
176 | char *p; |
c5fbd713 |
177 | int slen; |
7cca0d81 |
178 | char hash[20]; |
59600f67 |
179 | Bignum r, s, w, gu1p, yu2p, gu1yu2p, u1, u2, sha, v; |
7cca0d81 |
180 | int ret; |
181 | |
e055a386 |
182 | if (!dss->p) |
7cca0d81 |
183 | return 0; |
184 | |
9c621433 |
185 | #ifdef DEBUG_DSS |
186 | { |
187 | int i; |
188 | printf("sig:"); |
189 | for (i=0;i<siglen;i++) |
3709bfe9 |
190 | printf(" %02x", (unsigned char)(sig[i])); |
9c621433 |
191 | printf("\n"); |
192 | } |
193 | #endif |
7f7837c8 |
194 | /* |
195 | * Commercial SSH (2.0.13) and OpenSSH disagree over the format |
196 | * of a DSA signature. OpenSSH is in line with the IETF drafts: |
197 | * it uses a string "ssh-dss", followed by a 40-byte string |
198 | * containing two 160-bit integers end-to-end. Commercial SSH |
199 | * can't be bothered with the header bit, and considers a DSA |
200 | * signature blob to be _just_ the 40-byte string containing |
201 | * the two 160-bit integers. We tell them apart by measuring |
202 | * the length: length 40 means the commercial-SSH bug, anything |
203 | * else is assumed to be IETF-compliant. |
204 | */ |
205 | if (siglen != 40) { /* bug not present; read admin fields */ |
206 | getstring(&sig, &siglen, &p, &slen); |
efa4a6f2 |
207 | if (!p || slen != 7 || memcmp(p, "ssh-dss", 7)) { |
7f7837c8 |
208 | return 0; |
209 | } |
210 | sig += 4, siglen -= 4; /* skip yet another length field */ |
7cca0d81 |
211 | } |
e055a386 |
212 | diagbn("p=", dss->p); |
213 | diagbn("q=", dss->q); |
214 | diagbn("g=", dss->g); |
215 | diagbn("y=", dss->y); |
7cca0d81 |
216 | r = get160(&sig, &siglen); |
9c621433 |
217 | diagbn("r=", r); |
7cca0d81 |
218 | s = get160(&sig, &siglen); |
9c621433 |
219 | diagbn("s=", s); |
7cca0d81 |
220 | if (!r || !s) |
221 | return 0; |
222 | |
223 | /* |
224 | * Step 1. w <- s^-1 mod q. |
225 | */ |
e055a386 |
226 | w = modinv(s, dss->q); |
9c621433 |
227 | diagbn("w=", w); |
7cca0d81 |
228 | |
229 | /* |
230 | * Step 2. u1 <- SHA(message) * w mod q. |
231 | */ |
7cca0d81 |
232 | SHA_Simple(data, datalen, hash); |
233 | p = hash; slen = 20; sha = get160(&p, &slen); |
9c621433 |
234 | diagbn("sha=", sha); |
e055a386 |
235 | u1 = modmul(sha, w, dss->q); |
9c621433 |
236 | diagbn("u1=", u1); |
7cca0d81 |
237 | |
238 | /* |
239 | * Step 3. u2 <- r * w mod q. |
240 | */ |
e055a386 |
241 | u2 = modmul(r, w, dss->q); |
9c621433 |
242 | diagbn("u2=", u2); |
7cca0d81 |
243 | |
244 | /* |
245 | * Step 4. v <- (g^u1 * y^u2 mod p) mod q. |
246 | */ |
e055a386 |
247 | gu1p = modpow(dss->g, u1, dss->p); |
59600f67 |
248 | diagbn("gu1p=", gu1p); |
e055a386 |
249 | yu2p = modpow(dss->y, u2, dss->p); |
59600f67 |
250 | diagbn("yu2p=", yu2p); |
e055a386 |
251 | gu1yu2p = modmul(gu1p, yu2p, dss->p); |
59600f67 |
252 | diagbn("gu1yu2p=", gu1yu2p); |
e055a386 |
253 | v = modmul(gu1yu2p, One, dss->q); |
9c621433 |
254 | diagbn("gu1yu2q=v=", v); |
255 | diagbn("r=", r); |
7cca0d81 |
256 | |
257 | /* |
258 | * Step 5. v should now be equal to r. |
259 | */ |
260 | |
c5fbd713 |
261 | ret = !bignum_cmp(v, r); |
7cca0d81 |
262 | |
263 | freebn(w); |
7cca0d81 |
264 | freebn(sha); |
59600f67 |
265 | freebn(gu1p); |
266 | freebn(yu2p); |
267 | freebn(gu1yu2p); |
7cca0d81 |
268 | freebn(v); |
269 | freebn(r); |
270 | freebn(s); |
271 | |
272 | return ret; |
273 | } |
274 | |
e055a386 |
275 | int dss_sign(void *key, char *sig, int siglen, |
276 | char *data, int datalen) { |
277 | return 0; /* do nothing */ |
278 | } |
279 | |
280 | struct ssh_signkey ssh_dss = { |
281 | dss_newkey, |
282 | dss_freekey, |
7cca0d81 |
283 | dss_fmtkey, |
d5859615 |
284 | dss_fingerprint, |
7cca0d81 |
285 | dss_verifysig, |
e055a386 |
286 | dss_sign, |
d5859615 |
287 | "ssh-dss", |
288 | "dss" |
e5574168 |
289 | }; |