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 |
19 | #define DEBUG_DSS |
20 | /* |
21 | * Condition this section in for debugging of DSS. |
22 | */ |
23 | static void diagbn(char *prefix, Bignum md) { |
24 | int i, nibbles, morenibbles; |
25 | static const char hex[] = "0123456789ABCDEF"; |
26 | |
27 | printf("%s0x", prefix ? prefix : ""); |
28 | |
29 | nibbles = (3 + ssh1_bignum_bitcount(md))/4; if (nibbles<1) nibbles=1; |
30 | morenibbles = 4*md[0] - nibbles; |
31 | for (i=0; i<morenibbles; i++) putchar('-'); |
32 | for (i=nibbles; i-- ;) |
33 | putchar(hex[(bignum_byte(md, i/2) >> (4*(i%2))) & 0xF]); |
34 | |
35 | if (prefix) putchar('\n'); |
36 | } |
37 | #else |
38 | #define diagbn(x,y) |
39 | #endif |
40 | |
7cca0d81 |
41 | static void getstring(char **data, int *datalen, char **p, int *length) { |
42 | *p = NULL; |
43 | if (*datalen < 4) |
44 | return; |
45 | *length = GET_32BIT(*data); |
46 | *datalen -= 4; *data += 4; |
47 | if (*datalen < *length) |
48 | return; |
49 | *p = *data; |
50 | *data += *length; *datalen -= *length; |
51 | } |
52 | static Bignum getmp(char **data, int *datalen) { |
53 | char *p; |
54 | int i, j, length; |
55 | Bignum b; |
56 | |
57 | getstring(data, datalen, &p, &length); |
58 | if (!p) |
59 | return NULL; |
60 | if (p[0] & 0x80) |
61 | return NULL; /* negative mp */ |
62 | b = newbn((length+1)/2); |
63 | for (i = 0; i < length; i++) { |
64 | j = length - 1 - i; |
65 | if (j & 1) |
66 | b[j/2+1] |= ((unsigned char)p[i]) << 8; |
67 | else |
68 | b[j/2+1] |= ((unsigned char)p[i]); |
69 | } |
9c621433 |
70 | while (b[0] > 1 && b[b[0]] == 0) b[0]--; |
7cca0d81 |
71 | return b; |
72 | } |
73 | |
74 | static Bignum get160(char **data, int *datalen) { |
75 | char *p; |
76 | int i, j, length; |
77 | Bignum b; |
78 | |
79 | p = *data; |
80 | *data += 20; *datalen -= 20; |
81 | |
82 | length = 20; |
83 | while (length > 0 && !p[0]) |
84 | p++, length--; |
85 | b = newbn((length+1)/2); |
86 | for (i = 0; i < length; i++) { |
87 | j = length - 1 - i; |
88 | if (j & 1) |
89 | b[j/2+1] |= ((unsigned char)p[i]) << 8; |
90 | else |
91 | b[j/2+1] |= ((unsigned char)p[i]); |
92 | } |
93 | return b; |
94 | } |
95 | |
96 | static Bignum dss_p, dss_q, dss_g, dss_y; |
97 | |
98 | static void dss_setkey(char *data, int len) { |
99 | char *p; |
100 | int slen; |
101 | getstring(&data, &len, &p, &slen); |
9c621433 |
102 | |
103 | #ifdef DEBUG_DSS |
104 | { |
105 | int i; |
106 | printf("key:"); |
107 | for (i=0;i<len;i++) |
108 | printf(" %02x", (unsigned char)(data[i])); |
109 | printf("\n"); |
110 | } |
111 | #endif |
112 | |
7cca0d81 |
113 | if (!p || memcmp(p, "ssh-dss", 7)) { |
114 | dss_p = NULL; |
115 | return; |
116 | } |
117 | dss_p = getmp(&data, &len); |
118 | dss_q = getmp(&data, &len); |
119 | dss_g = getmp(&data, &len); |
120 | dss_y = getmp(&data, &len); |
121 | } |
122 | |
123 | static char *dss_fmtkey(void) { |
124 | char *p; |
d5859615 |
125 | int len, i, pos, nibbles; |
126 | static const char hex[] = "0123456789abcdef"; |
7cca0d81 |
127 | if (!dss_p) |
128 | return NULL; |
d5859615 |
129 | len = 8 + 4 + 1; /* 4 x "0x", punctuation, \0 */ |
7cca0d81 |
130 | len += 4 * (dss_p[0] + dss_q[0] + dss_g[0] + dss_y[0]); /* digits */ |
131 | p = malloc(len); |
132 | if (!p) return NULL; |
d5859615 |
133 | |
134 | pos = 0; |
135 | pos += sprintf(p+pos, "0x"); |
136 | nibbles = (3 + ssh1_bignum_bitcount(dss_p))/4; if (nibbles<1) nibbles=1; |
137 | for (i=nibbles; i-- ;) |
138 | p[pos++] = hex[(bignum_byte(dss_p, i/2) >> (4*(i%2))) & 0xF]; |
3aa0b691 |
139 | pos += sprintf(p+pos, ",0x"); |
d5859615 |
140 | nibbles = (3 + ssh1_bignum_bitcount(dss_q))/4; if (nibbles<1) nibbles=1; |
141 | for (i=nibbles; i-- ;) |
142 | p[pos++] = hex[(bignum_byte(dss_q, i/2) >> (4*(i%2))) & 0xF]; |
3aa0b691 |
143 | pos += sprintf(p+pos, ",0x"); |
d5859615 |
144 | nibbles = (3 + ssh1_bignum_bitcount(dss_g))/4; if (nibbles<1) nibbles=1; |
145 | for (i=nibbles; i-- ;) |
146 | p[pos++] = hex[(bignum_byte(dss_g, i/2) >> (4*(i%2))) & 0xF]; |
3aa0b691 |
147 | pos += sprintf(p+pos, ",0x"); |
d5859615 |
148 | nibbles = (3 + ssh1_bignum_bitcount(dss_y))/4; if (nibbles<1) nibbles=1; |
149 | for (i=nibbles; i-- ;) |
150 | p[pos++] = hex[(bignum_byte(dss_y, i/2) >> (4*(i%2))) & 0xF]; |
151 | p[pos] = '\0'; |
7cca0d81 |
152 | return p; |
153 | } |
154 | |
d5859615 |
155 | static char *dss_fingerprint(void) { |
156 | struct MD5Context md5c; |
157 | unsigned char digest[16], lenbuf[4]; |
158 | char buffer[16*3+40]; |
159 | char *ret; |
160 | int numlen, i; |
161 | |
162 | MD5Init(&md5c); |
163 | MD5Update(&md5c, "\0\0\0\7ssh-dss", 11); |
164 | |
165 | #define ADD_BIGNUM(bignum) \ |
166 | numlen = (ssh1_bignum_bitcount(bignum)+8)/8; \ |
167 | PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \ |
168 | for (i = numlen; i-- ;) { \ |
169 | unsigned char c = bignum_byte(bignum, i); \ |
170 | MD5Update(&md5c, &c, 1); \ |
171 | } |
172 | ADD_BIGNUM(dss_p); |
173 | ADD_BIGNUM(dss_q); |
174 | ADD_BIGNUM(dss_g); |
175 | ADD_BIGNUM(dss_y); |
176 | #undef ADD_BIGNUM |
177 | |
178 | MD5Final(digest, &md5c); |
179 | |
180 | sprintf(buffer, "%d ", ssh1_bignum_bitcount(dss_p)); |
181 | for (i = 0; i < 16; i++) |
182 | sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]); |
183 | ret = malloc(strlen(buffer)+1); |
184 | if (ret) |
185 | strcpy(ret, buffer); |
186 | return ret; |
187 | } |
188 | |
7cca0d81 |
189 | static int dss_verifysig(char *sig, int siglen, char *data, int datalen) { |
190 | char *p; |
191 | int i, slen; |
192 | char hash[20]; |
193 | Bignum qm2, r, s, w, i1, i2, i3, u1, u2, sha, v; |
194 | int ret; |
195 | |
196 | if (!dss_p) |
197 | return 0; |
198 | |
9c621433 |
199 | #ifdef DEBUG_DSS |
200 | { |
201 | int i; |
202 | printf("sig:"); |
203 | for (i=0;i<siglen;i++) |
204 | printf(" %02xf", (unsigned char)(sig[i])); |
205 | printf("\n"); |
206 | } |
207 | #endif |
7f7837c8 |
208 | /* |
209 | * Commercial SSH (2.0.13) and OpenSSH disagree over the format |
210 | * of a DSA signature. OpenSSH is in line with the IETF drafts: |
211 | * it uses a string "ssh-dss", followed by a 40-byte string |
212 | * containing two 160-bit integers end-to-end. Commercial SSH |
213 | * can't be bothered with the header bit, and considers a DSA |
214 | * signature blob to be _just_ the 40-byte string containing |
215 | * the two 160-bit integers. We tell them apart by measuring |
216 | * the length: length 40 means the commercial-SSH bug, anything |
217 | * else is assumed to be IETF-compliant. |
218 | */ |
219 | if (siglen != 40) { /* bug not present; read admin fields */ |
220 | getstring(&sig, &siglen, &p, &slen); |
221 | if (!p || memcmp(p, "ssh-dss", 7)) { |
222 | return 0; |
223 | } |
224 | sig += 4, siglen -= 4; /* skip yet another length field */ |
7cca0d81 |
225 | } |
9c621433 |
226 | diagbn("p=", dss_p); |
227 | diagbn("q=", dss_q); |
228 | diagbn("g=", dss_g); |
229 | diagbn("y=", dss_y); |
7cca0d81 |
230 | r = get160(&sig, &siglen); |
9c621433 |
231 | diagbn("r=", r); |
7cca0d81 |
232 | s = get160(&sig, &siglen); |
9c621433 |
233 | diagbn("s=", s); |
7cca0d81 |
234 | if (!r || !s) |
235 | return 0; |
236 | |
237 | /* |
238 | * Step 1. w <- s^-1 mod q. |
239 | */ |
240 | w = newbn(dss_q[0]); |
241 | qm2 = copybn(dss_q); |
242 | decbn(qm2); decbn(qm2); |
9c621433 |
243 | diagbn("qm2=", qm2); |
7cca0d81 |
244 | /* Now qm2 is q-2, and by Fermat's Little Theorem, s^qm2 == s^-1 (mod q). |
245 | * This is a silly way to do it; may fix it later. */ |
246 | modpow(s, qm2, dss_q, w); |
9c621433 |
247 | diagbn("w=", w); |
7cca0d81 |
248 | |
249 | /* |
250 | * Step 2. u1 <- SHA(message) * w mod q. |
251 | */ |
252 | u1 = newbn(dss_q[0]); |
253 | SHA_Simple(data, datalen, hash); |
254 | p = hash; slen = 20; sha = get160(&p, &slen); |
9c621433 |
255 | diagbn("sha=", sha); |
7cca0d81 |
256 | modmul(sha, w, dss_q, u1); |
9c621433 |
257 | diagbn("u1=", u1); |
7cca0d81 |
258 | |
259 | /* |
260 | * Step 3. u2 <- r * w mod q. |
261 | */ |
262 | u2 = newbn(dss_q[0]); |
263 | modmul(r, w, dss_q, u2); |
9c621433 |
264 | diagbn("u2=", u2); |
7cca0d81 |
265 | |
266 | /* |
267 | * Step 4. v <- (g^u1 * y^u2 mod p) mod q. |
268 | */ |
269 | i1 = newbn(dss_p[0]); |
270 | i2 = newbn(dss_p[0]); |
271 | i3 = newbn(dss_p[0]); |
272 | v = newbn(dss_q[0]); |
273 | modpow(dss_g, u1, dss_p, i1); |
9c621433 |
274 | diagbn("gu1p=", i1); |
7cca0d81 |
275 | modpow(dss_y, u2, dss_p, i2); |
9c621433 |
276 | diagbn("yu2p=", i2); |
7cca0d81 |
277 | modmul(i1, i2, dss_p, i3); |
9c621433 |
278 | diagbn("gu1yu2p=", i3); |
7cca0d81 |
279 | modmul(i3, One, dss_q, v); |
9c621433 |
280 | diagbn("gu1yu2q=v=", v); |
281 | diagbn("r=", r); |
7cca0d81 |
282 | |
283 | /* |
284 | * Step 5. v should now be equal to r. |
285 | */ |
286 | |
287 | ret = 1; |
288 | for (i = 1; i <= v[0] || i <= r[0]; i++) { |
289 | if ((i > v[0] && r[i] != 0) || |
290 | (i > r[0] && v[i] != 0) || |
291 | (i <= v[0] && i <= r[0] && r[i] != v[i])) |
292 | ret = 0; |
293 | } |
294 | |
295 | freebn(w); |
296 | freebn(qm2); |
297 | freebn(sha); |
298 | freebn(i1); |
299 | freebn(i2); |
300 | freebn(i3); |
301 | freebn(v); |
302 | freebn(r); |
303 | freebn(s); |
304 | |
305 | return ret; |
306 | } |
307 | |
e5574168 |
308 | struct ssh_hostkey ssh_dss = { |
7cca0d81 |
309 | dss_setkey, |
310 | dss_fmtkey, |
d5859615 |
311 | dss_fingerprint, |
7cca0d81 |
312 | dss_verifysig, |
d5859615 |
313 | "ssh-dss", |
314 | "dss" |
e5574168 |
315 | }; |