X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=blobdiff_plain;f=sshdh.c;h=8f8ab2d26aa6ef9ad7e5fe74710edca473272245;hb=a063e522970946bf7d5dc052079d7773c0dee76d;hp=f0abd3eca311131a57654fd1b35a1608179374e7;hpb=7958a63147b848a1951bafe3880e1510e620c94f;p=PuTTY.git

diff --git a/sshdh.c b/sshdh.c
index f0abd3ec..8f8ab2d2 100644
--- a/sshdh.c
+++ b/sshdh.c
@@ -52,7 +52,7 @@ static const unsigned char G[] = { 2 };
 
 static const struct ssh_kex ssh_diffiehellman_group1_sha1 = {
     "diffie-hellman-group1-sha1", "group1",
-    P1, G, lenof(P1), lenof(G), &ssh_sha1
+    KEXTYPE_DH, P1, G, lenof(P1), lenof(G), &ssh_sha1
 };
 
 static const struct ssh_kex *const group1_list[] = {
@@ -66,7 +66,7 @@ const struct ssh_kexes ssh_diffiehellman_group1 = {
 
 static const struct ssh_kex ssh_diffiehellman_group14_sha1 = {
     "diffie-hellman-group14-sha1", "group14",
-    P14, G, lenof(P14), lenof(G), &ssh_sha1
+    KEXTYPE_DH, P14, G, lenof(P14), lenof(G), &ssh_sha1
 };
 
 static const struct ssh_kex *const group14_list[] = {
@@ -80,12 +80,12 @@ const struct ssh_kexes ssh_diffiehellman_group14 = {
 
 static const struct ssh_kex ssh_diffiehellman_gex_sha256 = {
     "diffie-hellman-group-exchange-sha256", NULL,
-    NULL, NULL, 0, 0, &ssh_sha256
+    KEXTYPE_DH, NULL, NULL, 0, 0, &ssh_sha256
 };
 
 static const struct ssh_kex ssh_diffiehellman_gex_sha1 = {
     "diffie-hellman-group-exchange-sha1", NULL,
-    NULL, NULL, 0, 0, &ssh_sha1
+    KEXTYPE_DH, NULL, NULL, 0, 0, &ssh_sha1
 };
 
 static const struct ssh_kex *const gex_list[] = {
@@ -218,6 +218,29 @@ Bignum dh_create_e(void *handle, int nbits)
     return ctx->e;
 }
 
+/*
+ * DH stage 2-epsilon: given a number f, validate it to ensure it's in
+ * range. (RFC 4253 section 8: "Values of 'e' or 'f' that are not in
+ * the range [1, p-1] MUST NOT be sent or accepted by either side."
+ * Also, we rule out 1 and p-1 too, since that's easy to do and since
+ * they lead to obviously weak keys that even a passive eavesdropper
+ * can figure out.)
+ */
+const char *dh_validate_f(void *handle, Bignum f)
+{
+    struct dh_ctx *ctx = (struct dh_ctx *)handle;
+    if (bignum_cmp(f, One) <= 0) {
+        return "f value received is too small";
+    } else {
+        Bignum pm1 = bigsub(ctx->p, One);
+        int cmp = bignum_cmp(f, pm1);
+        freebn(pm1);
+        if (cmp >= 0)
+            return "f value received is too large";
+    }
+    return NULL;
+}
+
 /*
  * DH stage 2: given a number f, compute K = f^x mod p.
  */