From 7ba8196a3d22065aa35581fd8a82fc86c6779c0e Mon Sep 17 00:00:00 2001
From: John Safranek <john@wolfssl.com>
Date: Tue, 20 Apr 2021 14:00:47 -0700
Subject: [PATCH] Add missed step in DH key pair generation.

---
 wolfcrypt/src/dh.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/wolfcrypt/src/dh.c b/wolfcrypt/src/dh.c
index ca53e949d..c2fc9e3be 100644
--- a/wolfcrypt/src/dh.c
+++ b/wolfcrypt/src/dh.c
@@ -1144,10 +1144,16 @@ static int GeneratePrivateDh186(DhKey* key, WC_RNG* rng, byte* priv,
     ForceZero(cBuf, cSz);
     XFREE(cBuf, key->heap, DYNAMIC_TYPE_TMP_BUFFER);
 
-    /* tmpQ: M = 2^N - 1 */
+    /* tmpQ: M = min(2^N,q) - 1 */
     if (err == MP_OKAY)
         err = mp_2expt(tmpQ, *privSz * 8);
 
+    if (err == MP_OKAY) {
+        if (mp_cmp(tmpQ, &key->q) == MP_GT) {
+            err = mp_copy(&key->q, tmpQ);
+        }
+    }
+
     if (err == MP_OKAY)
         err = mp_sub_d(tmpQ, 1, tmpQ);