putty/sshdss.c

340 строки
8.9 KiB
C

#include <stdio.h>
#include <stdlib.h>
#include <assert.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); }
#if 0
#define DEBUG_DSS
#else
#define diagbn(x,y)
#endif
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 length;
Bignum b;
getstring(data, datalen, &p, &length);
if (!p)
return NULL;
if (p[0] & 0x80)
return NULL; /* negative mp */
b = bignum_from_bytes(p, length);
return b;
}
static Bignum get160(char **data, int *datalen) {
Bignum b;
b = bignum_from_bytes(*data, 20);
*data += 20; *datalen -= 20;
return b;
}
struct dss_key {
Bignum p, q, g, y;
};
static void *dss_newkey(char *data, int len) {
char *p;
int slen;
struct dss_key *dss;
dss = smalloc(sizeof(struct dss_key));
if (!dss) return NULL;
getstring(&data, &len, &p, &slen);
#ifdef DEBUG_DSS
{
int i;
printf("key:");
for (i=0;i<len;i++)
printf(" %02x", (unsigned char)(data[i]));
printf("\n");
}
#endif
if (!p || memcmp(p, "ssh-dss", 7)) {
sfree(dss);
return NULL;
}
dss->p = getmp(&data, &len);
dss->q = getmp(&data, &len);
dss->g = getmp(&data, &len);
dss->y = getmp(&data, &len);
return dss;
}
static void dss_freekey(void *key) {
struct dss_key *dss = (struct dss_key *)key;
freebn(dss->p);
freebn(dss->q);
freebn(dss->g);
freebn(dss->y);
sfree(dss);
}
static char *dss_fmtkey(void *key) {
struct dss_key *dss = (struct dss_key *)key;
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 * (ssh1_bignum_bitcount(dss->p)+15)/16;
len += 4 * (ssh1_bignum_bitcount(dss->q)+15)/16;
len += 4 * (ssh1_bignum_bitcount(dss->g)+15)/16;
len += 4 * (ssh1_bignum_bitcount(dss->y)+15)/16;
p = smalloc(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 *key) {
struct dss_key *dss = (struct dss_key *)key;
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, "ssh-dss %d ", ssh1_bignum_bitcount(dss->p));
for (i = 0; i < 16; i++)
sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]);
ret = smalloc(strlen(buffer)+1);
if (ret)
strcpy(ret, buffer);
return ret;
}
static int dss_verifysig(void *key, char *sig, int siglen,
char *data, int datalen) {
struct dss_key *dss = (struct dss_key *)key;
char *p;
int slen;
char hash[20];
Bignum r, s, w, gu1p, yu2p, gu1yu2p, u1, u2, sha, v;
int ret;
if (!dss->p)
return 0;
#ifdef DEBUG_DSS
{
int i;
printf("sig:");
for (i=0;i<siglen;i++)
printf(" %02x", (unsigned char)(sig[i]));
printf("\n");
}
#endif
/*
* 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 || slen != 7 || memcmp(p, "ssh-dss", 7)) {
return 0;
}
sig += 4, siglen -= 4; /* skip yet another length field */
}
diagbn("p=", dss->p);
diagbn("q=", dss->q);
diagbn("g=", dss->g);
diagbn("y=", dss->y);
r = get160(&sig, &siglen);
diagbn("r=", r);
s = get160(&sig, &siglen);
diagbn("s=", s);
if (!r || !s)
return 0;
/*
* Step 1. w <- s^-1 mod q.
*/
w = modinv(s, dss->q);
diagbn("w=", w);
/*
* Step 2. u1 <- SHA(message) * w mod q.
*/
SHA_Simple(data, datalen, hash);
p = hash; slen = 20; sha = get160(&p, &slen);
diagbn("sha=", sha);
u1 = modmul(sha, w, dss->q);
diagbn("u1=", u1);
/*
* Step 3. u2 <- r * w mod q.
*/
u2 = modmul(r, w, dss->q);
diagbn("u2=", u2);
/*
* Step 4. v <- (g^u1 * y^u2 mod p) mod q.
*/
gu1p = modpow(dss->g, u1, dss->p);
diagbn("gu1p=", gu1p);
yu2p = modpow(dss->y, u2, dss->p);
diagbn("yu2p=", yu2p);
gu1yu2p = modmul(gu1p, yu2p, dss->p);
diagbn("gu1yu2p=", gu1yu2p);
v = modmul(gu1yu2p, One, dss->q);
diagbn("gu1yu2q=v=", v);
diagbn("r=", r);
/*
* Step 5. v should now be equal to r.
*/
ret = !bignum_cmp(v, r);
freebn(w);
freebn(sha);
freebn(gu1p);
freebn(yu2p);
freebn(gu1yu2p);
freebn(v);
freebn(r);
freebn(s);
return ret;
}
static unsigned char *dss_public_blob(void *key, int *len) {
struct dss_key *dss = (struct dss_key *)key;
int plen, qlen, glen, ylen, bloblen;
int i;
unsigned char *blob, *p;
plen = (ssh1_bignum_bitcount(dss->p)+8)/8;
qlen = (ssh1_bignum_bitcount(dss->q)+8)/8;
glen = (ssh1_bignum_bitcount(dss->g)+8)/8;
ylen = (ssh1_bignum_bitcount(dss->y)+8)/8;
/*
* string "ssh-dss", mpint p, mpint q, mpint g, mpint y. Total
* 27 + sum of lengths. (five length fields, 20+7=27).
*/
bloblen = 27+plen+qlen+glen+ylen;
blob = smalloc(bloblen);
p = blob;
PUT_32BIT(p, 7); p += 4;
memcpy(p, "ssh-dss", 7); p += 7;
PUT_32BIT(p, plen); p += 4;
for (i = plen; i-- ;) *p++ = bignum_byte(dss->p, i);
PUT_32BIT(p, qlen); p += 4;
for (i = qlen; i-- ;) *p++ = bignum_byte(dss->q, i);
PUT_32BIT(p, glen); p += 4;
for (i = glen; i-- ;) *p++ = bignum_byte(dss->g, i);
PUT_32BIT(p, ylen); p += 4;
for (i = ylen; i-- ;) *p++ = bignum_byte(dss->y, i);
assert(p == blob + bloblen);
*len = bloblen;
return blob;
}
static unsigned char *dss_private_blob(void *key, int *len) {
return NULL; /* can't handle DSS private keys */
}
static void *dss_createkey(unsigned char *pub_blob, int pub_len,
unsigned char *priv_blob, int priv_len) {
return NULL; /* can't handle DSS private keys */
}
static void *dss_openssh_createkey(unsigned char **blob, int *len) {
return NULL; /* can't handle DSS private keys */
}
unsigned char *dss_sign(void *key, char *data, int datalen, int *siglen) {
return NULL; /* can't handle DSS private keys */
}
const struct ssh_signkey ssh_dss = {
dss_newkey,
dss_freekey,
dss_fmtkey,
dss_public_blob,
dss_private_blob,
dss_createkey,
dss_openssh_createkey,
dss_fingerprint,
dss_verifysig,
dss_sign,
"ssh-dss",
"dss"
};