+/*
+ * Digital Signature Standard implementation for PuTTY.
+ */
+
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include "ssh.h"
#include "misc.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 sha_mpint(SHA_State * s, Bignum b)
{
- unsigned char *p;
unsigned char lenbuf[4];
int len;
len = (bignum_bitcount(b) + 8) / 8;
lenbuf[0] = bignum_byte(b, len);
SHA_Bytes(s, lenbuf, 1);
}
- memset(lenbuf, 0, sizeof(lenbuf));
+ smemclr(lenbuf, sizeof(lenbuf));
}
static void sha512_mpint(SHA512_State * s, Bignum b)
{
- unsigned char *p;
unsigned char lenbuf[4];
int len;
len = (bignum_bitcount(b) + 8) / 8;
lenbuf[0] = bignum_byte(b, len);
SHA512_Bytes(s, lenbuf, 1);
}
- memset(lenbuf, 0, sizeof(lenbuf));
+ smemclr(lenbuf, sizeof(lenbuf));
}
static void getstring(char **data, int *datalen, char **p, int *length)
*p = NULL;
if (*datalen < 4)
return;
- *length = GET_32BIT(*data);
+ *length = toint(GET_32BIT(*data));
+ if (*length < 0)
+ return;
*datalen -= 4;
*data += 4;
if (*datalen < *length)
return NULL;
if (p[0] & 0x80)
return NULL; /* negative mp */
- b = bignum_from_bytes(p, length);
+ b = bignum_from_bytes((unsigned char *)p, length);
return b;
}
{
Bignum b;
- b = bignum_from_bytes(*data, 20);
+ if (*datalen < 20)
+ return NULL;
+
+ b = bignum_from_bytes((unsigned char *)*data, 20);
*data += 20;
*datalen -= 20;
return b;
}
+static void dss_freekey(void *key); /* forward reference */
+
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;
+ dss = snew(struct dss_key);
getstring(&data, &len, &p, &slen);
#ifdef DEBUG_DSS
}
#endif
- if (!p || memcmp(p, "ssh-dss", 7)) {
+ if (!p || slen != 7 || memcmp(p, "ssh-dss", 7)) {
sfree(dss);
return NULL;
}
dss->q = getmp(&data, &len);
dss->g = getmp(&data, &len);
dss->y = getmp(&data, &len);
+ dss->x = NULL;
+
+ if (!dss->p || !dss->q || !dss->g || !dss->y ||
+ !bignum_cmp(dss->q, Zero) || !bignum_cmp(dss->p, Zero)) {
+ /* Invalid key. */
+ dss_freekey(dss);
+ return NULL;
+ }
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);
+ if (dss->p)
+ freebn(dss->p);
+ if (dss->q)
+ freebn(dss->q);
+ if (dss->g)
+ freebn(dss->g);
+ if (dss->y)
+ freebn(dss->y);
+ if (dss->x)
+ freebn(dss->x);
sfree(dss);
}
len += 4 * (bignum_bitcount(dss->q) + 15) / 16;
len += 4 * (bignum_bitcount(dss->g) + 15) / 16;
len += 4 * (bignum_bitcount(dss->y) + 15) / 16;
- p = smalloc(len);
+ p = snewn(len, char);
if (!p)
return NULL;
int numlen, i;
MD5Init(&md5c);
- MD5Update(&md5c, "\0\0\0\7ssh-dss", 11);
+ MD5Update(&md5c, (unsigned char *)"\0\0\0\7ssh-dss", 11);
#define ADD_BIGNUM(bignum) \
numlen = (bignum_bitcount(bignum)+8)/8; \
for (i = 0; i < 16; i++)
sprintf(buffer + strlen(buffer), "%s%02x", i ? ":" : "",
digest[i]);
- ret = smalloc(strlen(buffer) + 1);
+ ret = snewn(strlen(buffer) + 1, char);
if (ret)
strcpy(ret, buffer);
return ret;
#endif
/*
* Commercial SSH (2.0.13) and OpenSSH disagree over the format
- * of a DSA signature. OpenSSH is in line with the IETF drafts:
+ * of a DSA signature. OpenSSH is in line with RFC 4253:
* 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.
+ * else is assumed to be RFC-compliant.
*/
if (siglen != 40) { /* bug not present; read admin fields */
getstring(&sig, &siglen, &p, &slen);
}
r = get160(&sig, &siglen);
s = get160(&sig, &siglen);
- if (!r || !s)
+ if (!r || !s) {
+ if (r)
+ freebn(r);
+ if (s)
+ freebn(s);
return 0;
+ }
+
+ if (!bignum_cmp(s, Zero)) {
+ freebn(r);
+ freebn(s);
+ return 0;
+ }
/*
* Step 1. w <- s^-1 mod q.
*/
w = modinv(s, dss->q);
+ if (!w) {
+ freebn(r);
+ freebn(s);
+ return 0;
+ }
/*
* Step 2. u1 <- SHA(message) * w mod q.
*/
- SHA_Simple(data, datalen, hash);
+ SHA_Simple(data, datalen, (unsigned char *)hash);
p = hash;
slen = 20;
sha = get160(&p, &slen);
freebn(w);
freebn(sha);
+ freebn(u1);
+ freebn(u2);
freebn(gu1p);
freebn(yu2p);
freebn(gu1yu2p);
* 27 + sum of lengths. (five length fields, 20+7=27).
*/
bloblen = 27 + plen + qlen + glen + ylen;
- blob = smalloc(bloblen);
+ blob = snewn(bloblen, unsigned char);
p = blob;
PUT_32BIT(p, 7);
p += 4;
int xlen, bloblen;
int i;
unsigned char *blob, *p;
- SHA_State s;
- unsigned char digest[20];
xlen = (bignum_bitcount(dss->x) + 8) / 8;
/*
- * mpint x, string[20] the SHA of p||q||g. Total 28 + xlen.
- * (two length fields and twenty bytes, 20+8=28).
+ * mpint x, string[20] the SHA of p||q||g. Total 4 + xlen.
*/
- bloblen = 28 + xlen;
- blob = smalloc(bloblen);
+ bloblen = 4 + xlen;
+ blob = snewn(bloblen, unsigned char);
p = blob;
PUT_32BIT(p, xlen);
p += 4;
for (i = xlen; i--;)
*p++ = bignum_byte(dss->x, i);
- PUT_32BIT(p, 20);
- SHA_Init(&s);
- sha_mpint(&s, dss->p);
- sha_mpint(&s, dss->q);
- sha_mpint(&s, dss->g);
- SHA_Final(&s, digest);
- p += 4;
- for (i = 0; i < 20; i++)
- *p++ = digest[i];
assert(p == blob + bloblen);
*len = bloblen;
return blob;
Bignum ytest;
dss = dss_newkey((char *) pub_blob, pub_len);
+ if (!dss)
+ return NULL;
dss->x = getmp(&pb, &priv_len);
- getstring(&pb, &priv_len, &hash, &hashlen);
+ if (!dss->x) {
+ dss_freekey(dss);
+ return NULL;
+ }
/*
- * Verify details of the key. First check that the hash is
- * indeed a hash of p||q||g.
+ * Check the obsolete hash in the old DSS key format.
*/
- if (hashlen != 20) {
- dss_freekey(dss);
- return NULL;
- }
- SHA_Init(&s);
- sha_mpint(&s, dss->p);
- sha_mpint(&s, dss->q);
- sha_mpint(&s, dss->g);
- SHA_Final(&s, digest);
- if (0 != memcmp(hash, digest, 20)) {
- dss_freekey(dss);
- return NULL;
+ hashlen = -1;
+ getstring(&pb, &priv_len, &hash, &hashlen);
+ if (hashlen == 20) {
+ SHA_Init(&s);
+ sha_mpint(&s, dss->p);
+ sha_mpint(&s, dss->q);
+ sha_mpint(&s, dss->g);
+ SHA_Final(&s, digest);
+ if (0 != memcmp(hash, digest, 20)) {
+ dss_freekey(dss);
+ return NULL;
+ }
}
/*
ytest = modpow(dss->g, dss->x, dss->p);
if (0 != bignum_cmp(ytest, dss->y)) {
dss_freekey(dss);
+ freebn(ytest);
return NULL;
}
freebn(ytest);
char **b = (char **) blob;
struct dss_key *dss;
- dss = smalloc(sizeof(struct dss_key));
- if (!dss)
- return NULL;
+ dss = snew(struct dss_key);
dss->p = getmp(b, len);
dss->q = getmp(b, len);
dss->y = getmp(b, len);
dss->x = getmp(b, len);
- if (!dss->p || !dss->q || !dss->g || !dss->y || !dss->x) {
- sfree(dss->p);
- sfree(dss->q);
- sfree(dss->g);
- sfree(dss->y);
- sfree(dss->x);
- sfree(dss);
- return NULL;
+ if (!dss->p || !dss->q || !dss->g || !dss->y || !dss->x ||
+ !bignum_cmp(dss->q, Zero) || !bignum_cmp(dss->p, Zero)) {
+ /* Invalid key. */
+ dss_freekey(dss);
+ return NULL;
}
return dss;
return bloblen;
}
-unsigned char *dss_sign(void *key, char *data, int datalen, int *siglen)
+static int dss_pubkey_bits(void *blob, int len)
+{
+ struct dss_key *dss;
+ int ret;
+
+ dss = dss_newkey((char *) blob, len);
+ if (!dss)
+ return -1;
+ ret = bignum_bitcount(dss->p);
+ dss_freekey(dss);
+
+ return ret;
+}
+
+static unsigned char *dss_sign(void *key, char *data, int datalen, int *siglen)
{
/*
* The basic DSS signing algorithm is:
* signing the same hash twice with the same key yields the
* same signature.
*
- * (It doesn't, _per se_, protect against reuse of k. Reuse of
- * k is left to chance; all it does is prevent _excessively
- * high_ chances of reuse of k due to entropy problems.)
+ * Despite this determinism, it's still not predictable to an
+ * attacker, because in order to repeat the SHA-512
+ * construction that created it, the attacker would have to
+ * know the private key value x - and by assumption he doesn't,
+ * because if he knew that he wouldn't be attacking k!
+ *
+ * (This trick doesn't, _per se_, protect against reuse of k.
+ * Reuse of k is left to chance; all it does is prevent
+ * _excessively high_ chances of reuse of k due to entropy
+ * problems.)
*
* Thanks to Colin Plumb for the general idea of using x to
* ensure k is hard to guess, and to the Cambridge University
SHA512_Init(&ss);
SHA512_Bytes(&ss, digest512, sizeof(digest512));
SHA512_Bytes(&ss, digest, sizeof(digest));
- SHA512_Final(&ss, digest512);
- memset(&ss, 0, sizeof(ss));
+ while (1) {
+ SHA512_State ss2 = ss; /* structure copy */
+ SHA512_Final(&ss2, digest512);
+
+ smemclr(&ss2, sizeof(ss2));
+
+ /*
+ * Now convert the result into a bignum, and reduce it mod q.
+ */
+ proto_k = bignum_from_bytes(digest512, 64);
+ k = bigmod(proto_k, dss->q);
+ freebn(proto_k);
+ kinv = modinv(k, dss->q); /* k^-1 mod q */
+ if (!kinv) { /* very unlikely */
+ freebn(k);
+ /* Perturb the hash to think of a different k. */
+ SHA512_Bytes(&ss, "x", 1);
+ /* Go round and try again. */
+ continue;
+ }
+
+ break;
+ }
- /*
- * Now convert the result into a bignum, and reduce it mod q.
- */
- proto_k = bignum_from_bytes(digest512, 64);
- k = bigmod(proto_k, dss->q);
- freebn(proto_k);
+ smemclr(&ss, sizeof(ss));
- memset(digest512, 0, sizeof(digest512));
+ smemclr(digest512, sizeof(digest512));
/*
* Now we have k, so just go ahead and compute the signature.
freebn(gkp);
hash = bignum_from_bytes(digest, 20);
- kinv = modinv(k, dss->q); /* k^-1 mod q */
hxr = bigmuladd(dss->x, r, hash); /* hash + x*r */
s = modmul(kinv, hxr, dss->q); /* s = k^-1 * (hash + x*r) mod q */
freebn(hxr);
freebn(kinv);
+ freebn(k);
freebn(hash);
/*
* i.e. 4+7 + 4+40 bytes.
*/
nbytes = 4 + 7 + 4 + 40;
- bytes = smalloc(nbytes);
+ bytes = snewn(nbytes, unsigned char);
PUT_32BIT(bytes, 7);
memcpy(bytes + 4, "ssh-dss", 7);
PUT_32BIT(bytes + 4 + 7, 40);
dss_createkey,
dss_openssh_createkey,
dss_openssh_fmtkey,
+ dss_pubkey_bits,
dss_fingerprint,
dss_verifysig,
dss_sign,
projects / u / mdw / putty / blobdiff