#include <stdio.h>
#include <stdlib.h>
#include "ssh.h"
#define GET_32BIT(cp) \
(((unsigned long)(unsigned char)(cp)[0] << 24) | \
((unsigned long)(unsigned char)(cp)[1] << 16) | \
((unsigned long)(unsigned char)(cp)[2] << 8) | \
((unsigned long)(unsigned char)(cp)[3]))
#define PUT_32BIT(cp, value) { \
(cp)[0] = (unsigned char)((value) >> 24); \
(cp)[1] = (unsigned char)((value) >> 16); \
(cp)[2] = (unsigned char)((value) >> 8); \
(cp)[3] = (unsigned char)(value); }
static void getstring(char **data, int *datalen, char **p, int *length) {
*p = NULL;
if (*datalen < 4)
return;
*length = GET_32BIT(*data);
*datalen -= 4; *data += 4;
if (*datalen < *length)
return;
*p = *data;
*data += *length; *datalen -= *length;
}
static Bignum getmp(char **data, int *datalen) {
char *p;
int i, j, length;
Bignum b;
getstring(data, datalen, &p, &length);
if (!p)
return NULL;
if (p[0] & 0x80)
return NULL; /* negative mp */
b = newbn((length+1)/2);
for (i = 0; i < length; i++) {
j = length - 1 - i;
if (j & 1)
b[j/2+1] |= ((unsigned char)p[i]) << 8;
else
b[j/2+1] |= ((unsigned char)p[i]);
}
return b;
}
static Bignum get160(char **data, int *datalen) {
char *p;
int i, j, length;
Bignum b;
p = *data;
*data += 20; *datalen -= 20;
length = 20;
while (length > 0 && !p[0])
p++, length--;
b = newbn((length+1)/2);
for (i = 0; i < length; i++) {
j = length - 1 - i;
if (j & 1)
b[j/2+1] |= ((unsigned char)p[i]) << 8;
else
b[j/2+1] |= ((unsigned char)p[i]);
}
return b;
}
static Bignum dss_p, dss_q, dss_g, dss_y;
static void dss_setkey(char *data, int len) {
char *p;
int slen;
getstring(&data, &len, &p, &slen);
if (!p || memcmp(p, "ssh-dss", 7)) {
dss_p = NULL;
return;
}
dss_p = getmp(&data, &len);
dss_q = getmp(&data, &len);
dss_g = getmp(&data, &len);
dss_y = getmp(&data, &len);
}
static char *dss_fmtkey(void) {
char *p;
int len, i, pos, nibbles;
static const char hex[] = "0123456789abcdef";
if (!dss_p)
return NULL;
len = 8 + 4 + 1; /* 4 x "0x", punctuation, \0 */
len += 4 * (dss_p[0] + dss_q[0] + dss_g[0] + dss_y[0]); /* digits */
p = malloc(len);
if (!p) return NULL;
pos = 0;
pos += sprintf(p+pos, "0x");
nibbles = (3 + ssh1_bignum_bitcount(dss_p))/4; if (nibbles<1) nibbles=1;
for (i=nibbles; i-- ;)
p[pos++] = hex[(bignum_byte(dss_p, i/2) >> (4*(i%2))) & 0xF];
pos += sprintf(p+pos, ",0x");
nibbles = (3 + ssh1_bignum_bitcount(dss_q))/4; if (nibbles<1) nibbles=1;
for (i=nibbles; i-- ;)
p[pos++] = hex[(bignum_byte(dss_q, i/2) >> (4*(i%2))) & 0xF];
pos += sprintf(p+pos, ",0x");
nibbles = (3 + ssh1_bignum_bitcount(dss_g))/4; if (nibbles<1) nibbles=1;
for (i=nibbles; i-- ;)
p[pos++] = hex[(bignum_byte(dss_g, i/2) >> (4*(i%2))) & 0xF];
pos += sprintf(p+pos, ",0x");
nibbles = (3 + ssh1_bignum_bitcount(dss_y))/4; if (nibbles<1) nibbles=1;
for (i=nibbles; i-- ;)
p[pos++] = hex[(bignum_byte(dss_y, i/2) >> (4*(i%2))) & 0xF];
p[pos] = '\0';
return p;
}
static char *dss_fingerprint(void) {
struct MD5Context md5c;
unsigned char digest[16], lenbuf[4];
char buffer[16*3+40];
char *ret;
int numlen, i;
MD5Init(&md5c);
MD5Update(&md5c, "\0\0\0\7ssh-dss", 11);
#define ADD_BIGNUM(bignum) \
numlen = (ssh1_bignum_bitcount(bignum)+8)/8; \
PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \
for (i = numlen; i-- ;) { \
unsigned char c = bignum_byte(bignum, i); \
MD5Update(&md5c, &c, 1); \
}
ADD_BIGNUM(dss_p);
ADD_BIGNUM(dss_q);
ADD_BIGNUM(dss_g);
ADD_BIGNUM(dss_y);
#undef ADD_BIGNUM
MD5Final(digest, &md5c);
sprintf(buffer, "%d ", ssh1_bignum_bitcount(dss_p));
for (i = 0; i < 16; i++)
sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]);
ret = malloc(strlen(buffer)+1);
if (ret)
strcpy(ret, buffer);
return ret;
}
static int dss_verifysig(char *sig, int siglen, char *data, int datalen) {
char *p;
int i, slen;
char hash[20];
Bignum qm2, r, s, w, i1, i2, i3, u1, u2, sha, v;
int ret;
if (!dss_p)
return 0;
/*
* Commercial SSH (2.0.13) and OpenSSH disagree over the format
* of a DSA signature. OpenSSH is in line with the IETF drafts:
* it uses a string "ssh-dss", followed by a 40-byte string
* containing two 160-bit integers end-to-end. Commercial SSH
* can't be bothered with the header bit, and considers a DSA
* signature blob to be _just_ the 40-byte string containing
* the two 160-bit integers. We tell them apart by measuring
* the length: length 40 means the commercial-SSH bug, anything
* else is assumed to be IETF-compliant.
*/
if (siglen != 40) { /* bug not present; read admin fields */
getstring(&sig, &siglen, &p, &slen);
if (!p || memcmp(p, "ssh-dss", 7)) {
return 0;
}
sig += 4, siglen -= 4; /* skip yet another length field */
}
r = get160(&sig, &siglen);
s = get160(&sig, &siglen);
if (!r || !s)
return 0;
/*
* Step 1. w <- s^-1 mod q.
*/
w = newbn(dss_q[0]);
qm2 = copybn(dss_q);
decbn(qm2); decbn(qm2);
/* Now qm2 is q-2, and by Fermat's Little Theorem, s^qm2 == s^-1 (mod q).
* This is a silly way to do it; may fix it later. */
modpow(s, qm2, dss_q, w);
/*
* Step 2. u1 <- SHA(message) * w mod q.
*/
u1 = newbn(dss_q[0]);
SHA_Simple(data, datalen, hash);
p = hash; slen = 20; sha = get160(&p, &slen);
modmul(sha, w, dss_q, u1);
/*
* Step 3. u2 <- r * w mod q.
*/
u2 = newbn(dss_q[0]);
modmul(r, w, dss_q, u2);
/*
* Step 4. v <- (g^u1 * y^u2 mod p) mod q.
*/
i1 = newbn(dss_p[0]);
i2 = newbn(dss_p[0]);
i3 = newbn(dss_p[0]);
v = newbn(dss_q[0]);
modpow(dss_g, u1, dss_p, i1);
modpow(dss_y, u2, dss_p, i2);
modmul(i1, i2, dss_p, i3);
modmul(i3, One, dss_q, v);
/*
* Step 5. v should now be equal to r.
*/
ret = 1;
for (i = 1; i <= v[0] || i <= r[0]; i++) {
if ((i > v[0] && r[i] != 0) ||
(i > r[0] && v[i] != 0) ||
(i <= v[0] && i <= r[0] && r[i] != v[i]))
ret = 0;
}
freebn(w);
freebn(qm2);
freebn(sha);
freebn(i1);
freebn(i2);
freebn(i3);
freebn(v);
freebn(r);
freebn(s);
return ret;
}
struct ssh_hostkey ssh_dss = {
dss_setkey,
dss_fmtkey,
dss_fingerprint,
dss_verifysig,
"ssh-dss",
"dss"
};