+#include <stdio.h>
+#include <stdlib.h>
+
#include "ssh.h"
-struct ssh_hostkey ssh_dss = {
- "ssh-dss"
+#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, "%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 || 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;
+}
+
+int dss_sign(void *key, char *sig, int siglen,
+ char *data, int datalen) {
+ return 0; /* do nothing */
+}
+
+struct ssh_signkey ssh_dss = {
+ dss_newkey,
+ dss_freekey,
+ dss_fmtkey,
+ dss_fingerprint,
+ dss_verifysig,
+ dss_sign,
+ "ssh-dss",
+ "dss"
};
projects / u / mdw / putty / blobdiff