+#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]))
+
+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;
+ int i;
+ if (!dss_p)
+ return NULL;
+ len = 7 + 4 + 1; /* "ssh-dss", punctuation, \0 */
+ len += 4 * (dss_p[0] + dss_q[0] + dss_g[0] + dss_y[0]); /* digits */
+ p = malloc(len);
+ if (!p) return NULL;
+ strcpy(p, "ssh-dss:");
+ for (i = dss_p[0]; i > 0; i--) sprintf(p+strlen(p), "%04X", dss_p[i]);
+ strcat(p, "/");
+ for (i = dss_q[0]; i > 0; i--) sprintf(p+strlen(p), "%04X", dss_q[i]);
+ strcat(p, "/");
+ for (i = dss_g[0]; i > 0; i--) sprintf(p+strlen(p), "%04X", dss_g[i]);
+ strcat(p, "/");
+ for (i = dss_y[0]; i > 0; i--) sprintf(p+strlen(p), "%04X", dss_y[i]);
+ return p;
+}
+
+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;
+
+ 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_verifysig,
"ssh-dss"
};