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 | |
12 | static void getstring(char **data, int *datalen, char **p, int *length) { |
13 | *p = NULL; |
14 | if (*datalen < 4) |
15 | return; |
16 | *length = GET_32BIT(*data); |
17 | *datalen -= 4; *data += 4; |
18 | if (*datalen < *length) |
19 | return; |
20 | *p = *data; |
21 | *data += *length; *datalen -= *length; |
22 | } |
23 | static Bignum getmp(char **data, int *datalen) { |
24 | char *p; |
25 | int i, j, length; |
26 | Bignum b; |
27 | |
28 | getstring(data, datalen, &p, &length); |
29 | if (!p) |
30 | return NULL; |
31 | if (p[0] & 0x80) |
32 | return NULL; /* negative mp */ |
33 | b = newbn((length+1)/2); |
34 | for (i = 0; i < length; i++) { |
35 | j = length - 1 - i; |
36 | if (j & 1) |
37 | b[j/2+1] |= ((unsigned char)p[i]) << 8; |
38 | else |
39 | b[j/2+1] |= ((unsigned char)p[i]); |
40 | } |
41 | return b; |
42 | } |
43 | |
44 | static Bignum get160(char **data, int *datalen) { |
45 | char *p; |
46 | int i, j, length; |
47 | Bignum b; |
48 | |
49 | p = *data; |
50 | *data += 20; *datalen -= 20; |
51 | |
52 | length = 20; |
53 | while (length > 0 && !p[0]) |
54 | p++, length--; |
55 | b = newbn((length+1)/2); |
56 | for (i = 0; i < length; i++) { |
57 | j = length - 1 - i; |
58 | if (j & 1) |
59 | b[j/2+1] |= ((unsigned char)p[i]) << 8; |
60 | else |
61 | b[j/2+1] |= ((unsigned char)p[i]); |
62 | } |
63 | return b; |
64 | } |
65 | |
66 | static Bignum dss_p, dss_q, dss_g, dss_y; |
67 | |
68 | static void dss_setkey(char *data, int len) { |
69 | char *p; |
70 | int slen; |
71 | getstring(&data, &len, &p, &slen); |
72 | if (!p || memcmp(p, "ssh-dss", 7)) { |
73 | dss_p = NULL; |
74 | return; |
75 | } |
76 | dss_p = getmp(&data, &len); |
77 | dss_q = getmp(&data, &len); |
78 | dss_g = getmp(&data, &len); |
79 | dss_y = getmp(&data, &len); |
80 | } |
81 | |
82 | static char *dss_fmtkey(void) { |
83 | char *p; |
84 | int len; |
85 | int i; |
86 | if (!dss_p) |
87 | return NULL; |
88 | len = 7 + 4 + 1; /* "ssh-dss", punctuation, \0 */ |
89 | len += 4 * (dss_p[0] + dss_q[0] + dss_g[0] + dss_y[0]); /* digits */ |
90 | p = malloc(len); |
91 | if (!p) return NULL; |
92 | strcpy(p, "ssh-dss:"); |
93 | for (i = dss_p[0]; i > 0; i--) sprintf(p+strlen(p), "%04X", dss_p[i]); |
94 | strcat(p, "/"); |
95 | for (i = dss_q[0]; i > 0; i--) sprintf(p+strlen(p), "%04X", dss_q[i]); |
96 | strcat(p, "/"); |
97 | for (i = dss_g[0]; i > 0; i--) sprintf(p+strlen(p), "%04X", dss_g[i]); |
98 | strcat(p, "/"); |
99 | for (i = dss_y[0]; i > 0; i--) sprintf(p+strlen(p), "%04X", dss_y[i]); |
100 | return p; |
101 | } |
102 | |
103 | static int dss_verifysig(char *sig, int siglen, char *data, int datalen) { |
104 | char *p; |
105 | int i, slen; |
106 | char hash[20]; |
107 | Bignum qm2, r, s, w, i1, i2, i3, u1, u2, sha, v; |
108 | int ret; |
109 | |
110 | if (!dss_p) |
111 | return 0; |
112 | |
113 | getstring(&sig, &siglen, &p, &slen); |
114 | if (!p || memcmp(p, "ssh-dss", 7)) { |
115 | return 0; |
116 | } |
117 | sig += 4, siglen -= 4; /* skip yet another length field */ |
118 | r = get160(&sig, &siglen); |
119 | s = get160(&sig, &siglen); |
120 | if (!r || !s) |
121 | return 0; |
122 | |
123 | /* |
124 | * Step 1. w <- s^-1 mod q. |
125 | */ |
126 | w = newbn(dss_q[0]); |
127 | qm2 = copybn(dss_q); |
128 | decbn(qm2); decbn(qm2); |
129 | /* Now qm2 is q-2, and by Fermat's Little Theorem, s^qm2 == s^-1 (mod q). |
130 | * This is a silly way to do it; may fix it later. */ |
131 | modpow(s, qm2, dss_q, w); |
132 | |
133 | /* |
134 | * Step 2. u1 <- SHA(message) * w mod q. |
135 | */ |
136 | u1 = newbn(dss_q[0]); |
137 | SHA_Simple(data, datalen, hash); |
138 | p = hash; slen = 20; sha = get160(&p, &slen); |
139 | modmul(sha, w, dss_q, u1); |
140 | |
141 | /* |
142 | * Step 3. u2 <- r * w mod q. |
143 | */ |
144 | u2 = newbn(dss_q[0]); |
145 | modmul(r, w, dss_q, u2); |
146 | |
147 | /* |
148 | * Step 4. v <- (g^u1 * y^u2 mod p) mod q. |
149 | */ |
150 | i1 = newbn(dss_p[0]); |
151 | i2 = newbn(dss_p[0]); |
152 | i3 = newbn(dss_p[0]); |
153 | v = newbn(dss_q[0]); |
154 | modpow(dss_g, u1, dss_p, i1); |
155 | modpow(dss_y, u2, dss_p, i2); |
156 | modmul(i1, i2, dss_p, i3); |
157 | modmul(i3, One, dss_q, v); |
158 | |
159 | /* |
160 | * Step 5. v should now be equal to r. |
161 | */ |
162 | |
163 | ret = 1; |
164 | for (i = 1; i <= v[0] || i <= r[0]; i++) { |
165 | if ((i > v[0] && r[i] != 0) || |
166 | (i > r[0] && v[i] != 0) || |
167 | (i <= v[0] && i <= r[0] && r[i] != v[i])) |
168 | ret = 0; |
169 | } |
170 | |
171 | freebn(w); |
172 | freebn(qm2); |
173 | freebn(sha); |
174 | freebn(i1); |
175 | freebn(i2); |
176 | freebn(i3); |
177 | freebn(v); |
178 | freebn(r); |
179 | freebn(s); |
180 | |
181 | return ret; |
182 | } |
183 | |
e5574168 |
184 | struct ssh_hostkey ssh_dss = { |
7cca0d81 |
185 | dss_setkey, |
186 | dss_fmtkey, |
187 | dss_verifysig, |
e5574168 |
188 | "ssh-dss" |
189 | }; |