From 65cd8a930e7c1a537375606dd5e519b6211597a5 Mon Sep 17 00:00:00 2001
From: Sean Parkinson <sean@wolfssl.com>
Date: Wed, 6 Nov 2019 15:24:12 +1000
Subject: [PATCH] SP Math and RSA Key Gen working again

---
 wolfcrypt/src/sp_int.c     | 30 ++++++++++++++++++++++++------
 wolfssl/wolfcrypt/sp_int.h |  2 ++
 2 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/wolfcrypt/src/sp_int.c b/wolfcrypt/src/sp_int.c
index eced17dd0..4b9ab4eb1 100644
--- a/wolfcrypt/src/sp_int.c
+++ b/wolfcrypt/src/sp_int.c
@@ -1067,7 +1067,7 @@ static int sp_sqrmod(sp_int* a, sp_int* m, sp_int* r)
     return err;
 }
 
-#if defined(WOLFSSL_HAVE_SP_DH) && defined(WOLFSSL_KEY_GEN)
+#if defined(WOLFSSL_HAVE_SP_DH) || defined(WOLFSSL_KEY_GEN)
 /* Multiply a by b mod m and store in r: r = (a * b) mod m
  *
  * a  SP integer to multiply.
@@ -1077,14 +1077,32 @@ static int sp_sqrmod(sp_int* a, sp_int* m, sp_int* r)
  * returns MP_VAL when m is 0, MP_MEM when dynamic memory allocation fails and
  *         MP_OKAY otherwise.
  */
-static int sp_mulmod(sp_int* a, sp_int* b, sp_int* m, sp_int* r)
+int sp_mulmod(sp_int* a, sp_int* b, sp_int* m, sp_int* r)
 {
-    int err;
+    int err = MP_OKAY;
+#ifdef WOLFSSL_SMALL_STACK
+    sp_int* t;
+#else
+    sp_int t[1];
+#endif
 
-    err = sp_mul(a, b, r);
-    if (err == MP_OKAY)
-        err = sp_mod(r, m, r);
+#ifdef WOLFSSL_SMALL_STACK
+    t = (sp_int*)XMALLOC(sizeof(sp_int), NULL, DYNAMIC_TYPE_BIGINT);
+    if (t == NULL) {
+        err = MP_MEM;
+    }
+#endif
+    if (err == MP_OKAY) {
+        err = sp_mul(a, b, t);
+    }
+    if (err == MP_OKAY) {
+        err = sp_mod(t, m, r);
+    }
 
+#ifdef WOLFSSL_SMALL_STACK
+    if (t != NULL)
+        XFREE(t, NULL, DYNAMIC_TYPE_BIGINT);
+#endif
     return err;
 }
 #endif
diff --git a/wolfssl/wolfcrypt/sp_int.h b/wolfssl/wolfcrypt/sp_int.h
index 6552d7cf5..ed8e0fe1c 100644
--- a/wolfssl/wolfcrypt/sp_int.h
+++ b/wolfssl/wolfcrypt/sp_int.h
@@ -180,6 +180,7 @@ MP_API int sp_tohex(sp_int* a, char* str);
 MP_API int sp_2expt(sp_int* a, int e);
 MP_API int sp_rand_prime(sp_int* r, int len, WC_RNG* rng, void* heap);
 MP_API int sp_mul(sp_int* a, sp_int* b, sp_int* r);
+MP_API int sp_mulmod(sp_int* a, sp_int* b, sp_int* m, sp_int* r);
 MP_API int sp_gcd(sp_int* a, sp_int* b, sp_int* r);
 MP_API int sp_invmod(sp_int* a, sp_int* m, sp_int* r);
 MP_API int sp_lcm(sp_int* a, sp_int* b, sp_int* r);
@@ -246,6 +247,7 @@ MP_API void sp_rshb(sp_int* a, int n, sp_int* r);
 #define mp_2expt                    sp_2expt
 #define mp_rand_prime               sp_rand_prime
 #define mp_mul                      sp_mul
+#define mp_mulmod                   sp_mulmod
 #define mp_gcd                      sp_gcd
 #define mp_invmod                   sp_invmod
 #define mp_lcm                      sp_lcm