+#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); }
+
+#if 0
+#define DEBUG_DSS
+/*
+ * Condition this section in for debugging of DSS.
+ */
+static void diagbn(char *prefix, Bignum md) {
+ int i, nibbles, morenibbles;
+ static const char hex[] = "0123456789ABCDEF";
+
+ printf("%s0x", prefix ? prefix : "");
+
+ nibbles = (3 + ssh1_bignum_bitcount(md))/4; if (nibbles<1) nibbles=1;
+ morenibbles = 4*md[0] - nibbles;
+ for (i=0; i<morenibbles; i++) putchar('-');
+ for (i=nibbles; i-- ;)
+ putchar(hex[(bignum_byte(md, i/2) >> (4*(i%2))) & 0xF]);
+
+ if (prefix) putchar('\n');
+}
+#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 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]);
+ }
+ while (b[0] > 1 && b[b[0]] == 0) b[0]--;
+ 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);
+
+#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)) {
+ 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;
+
+#ifdef DEBUG_DSS
+ {
+ int i;
+ printf("sig:");
+ for (i=0;i<siglen;i++)
+ printf(" %02xf", (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 = newbn(dss_q[0]);
+ qm2 = copybn(dss_q);
+ decbn(qm2); decbn(qm2);
+ diagbn("qm2=", 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);
+ diagbn("w=", 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);
+ diagbn("sha=", sha);
+ modmul(sha, w, dss_q, u1);
+ diagbn("u1=", u1);
+
+ /*
+ * Step 3. u2 <- r * w mod q.
+ */
+ u2 = newbn(dss_q[0]);
+ modmul(r, w, dss_q, u2);
+ diagbn("u2=", 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);
+ diagbn("gu1p=", i1);
+ modpow(dss_y, u2, dss_p, i2);
+ diagbn("yu2p=", i2);
+ modmul(i1, i2, dss_p, i3);
+ diagbn("gu1yu2p=", i3);
+ modmul(i3, One, dss_q, v);
+ diagbn("gu1yu2q=v=", v);
+ diagbn("r=", r);
+
+ /*
+ * 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 = {
- "ssh-dss"
+ dss_setkey,
+ dss_fmtkey,
+ dss_fingerprint,
+ dss_verifysig,
+ "ssh-dss",
+ "dss"
};
projects / u / mdw / putty / blobdiff