| 1 | #include <stdio.h> |
| 2 | #include <stdlib.h> |
| 3 | |
| 4 | #include "ssh.h" |
| 5 | |
| 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 | |
| 184 | struct ssh_hostkey ssh_dss = { |
| 185 | dss_setkey, |
| 186 | dss_fmtkey, |
| 187 | dss_verifysig, |
| 188 | "ssh-dss" |
| 189 | }; |