X-Git-Url: https://git.distorted.org.uk/u/mdw/putty/blobdiff_plain/e557416818242c2e8b14ec03d321740fd83619e4..3709bfe9981af43e3cd491c37d300b57e5b26d50:/sshdss.c

diff --git a/sshdss.c b/sshdss.c
index c651140e..cf7fc3f7 100644
--- a/sshdss.c
+++ b/sshdss.c
@@ -1,5 +1,289 @@
+#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"
 };