Enhance Diffie-Hellman implementation to use bignum_cmp

git-svn-id: svn://svn.tartarus.org/sgt/putty@762 cda61777-01e9-0310-a592-d414129be87e

diff --git a/sshdh.c b/sshdh.c
index 84035c0..dabed52 100644 (file)
--- a/sshdh.c
+++ b/sshdh.c
@@ -68,33 +68,14 @@ Bignum dh_create_e(void) {
 
     x = newbn(Q[0]);
 
-    tryagain:
-
-    /*
-     * Create a potential x, by ANDing a string of random bytes
-     * with Qmask.
-     */
-    for (i = 1; i <= x[0]; i++)
-        x[i] = ((random_byte() << 8) + random_byte()) & Qmask[i];
-
-    /*
-     * If x <= 1, go round again.
-     */
-    for (i = 2; i <= x[0]; i++)
-        if (x[i] != 0)
-            break;
-    if (i > x[0] && x[1] <= 1)
-        goto tryagain;
-
-    /*
-     * If x >= q, go round again.
-     */
-    for (i = x[0]; i > 0; i--) {
-        if (x[i] > Q[i])
-            goto tryagain;
-        if (x[i] < Q[i])
-            break;
-    }
+    do {
+       /*
+        * Create a potential x, by ANDing a string of random bytes
+        * with Qmask.
+        */
+       for (i = 1; i <= x[0]; i++)
+           x[i] = ((random_byte() << 8) + random_byte()) & Qmask[i];
+    } while (bignum_cmp(x, One) <= 0 || bignum_cmp(x, Q) >= 0);
 
     /*
      * Done. Now compute e = g^x mod p.
@@ -108,7 +89,5 @@ Bignum dh_create_e(void) {
  * DH stage 2: given a number f, compute K = f^x mod p.
  */
 Bignum dh_find_K(Bignum f) {
-    Bignum K = newbn(P[0]);
-    K = modpow(f, x, P);
-    return K;
+    return modpow(f, x, P);
 }