X-Git-Url: https://git.distorted.org.uk/u/mdw/putty/blobdiff_plain/033b4cef1e52d65786b00df47f57361b96ca4321..7cca0d811c4d1b5bb346cd60fdfa461a558aefec:/sshdss.c

diff --git a/sshdss.c b/sshdss.c
index c651140e..ce18f472 100644
--- a/sshdss.c
+++ b/sshdss.c
@@ -1,5 +1,189 @@
+#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"
 };