From 2e1e8d27892e64eb6446a94333fd88c6a454b781 Mon Sep 17 00:00:00 2001
From: Marco Oliverio <marco@wolfssl.com>
Date: Mon, 25 Jul 2022 17:48:26 +0200
Subject: [PATCH] misc.c: introduce ctMaskCopy()

---
 wolfcrypt/src/misc.c     | 11 +++++++++++
 wolfssl/wolfcrypt/misc.h |  2 ++
 2 files changed, 13 insertions(+)

diff --git a/wolfcrypt/src/misc.c b/wolfcrypt/src/misc.c
index da2778ea9..7d534ffde 100644
--- a/wolfcrypt/src/misc.c
+++ b/wolfcrypt/src/misc.c
@@ -544,6 +544,17 @@ WC_STATIC WC_INLINE byte ctSetLTE(int a, int b)
 {
     return (byte)(((word32)a - b - 1) >> 31);
 }
+
+/* Constant time - copy size bytes from left to dst if mask is set, size bytes
+ * from right to dst if mask is not set */
+WC_STATIC WC_INLINE void ctMaskCopy(byte m, byte* dst, byte* left, byte* right,
+    word16 size)
+{
+    int i;
+    for (i = 0; i < size; ++i)
+        dst[i] = ctMaskSel(m, left[i], right[i]);
+}
+
 #endif
 
 #if defined(WOLFSSL_W64_WRAPPER)
diff --git a/wolfssl/wolfcrypt/misc.h b/wolfssl/wolfcrypt/misc.h
index 03312bfcc..d0231e5ff 100644
--- a/wolfssl/wolfcrypt/misc.h
+++ b/wolfssl/wolfcrypt/misc.h
@@ -126,6 +126,8 @@ WOLFSSL_LOCAL byte ctMaskNotEq(int a, int b);
 WOLFSSL_LOCAL byte ctMaskSel(byte m, byte a, byte b);
 WOLFSSL_LOCAL int  ctMaskSelInt(byte m, int a, int b);
 WOLFSSL_LOCAL byte ctSetLTE(int a, int b);
+WOLFSSL_LOCAL void ctMaskCopy(byte m, byte* dst, byte* left, byte* right,
+    word16 size);
 
 #endif /* NO_INLINE */