Add SHA-256 source specific for upcoming bootloader build because of its small size. It was derived from the libtomcrypt public domain source.

src/Crypto/Sha2Small.h

@@ -0,0 +1,55 @@
+/* LibTomCrypt, modular cryptographic library -- Tom St Denis
+ *
+ * LibTomCrypt is a library that provides various cryptographic
+ * algorithms in a highly modular and flexible manner.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ *
+ * Tom St Denis, tomstdenis@gmail.com, http://libtom.org
+ *
+ */
+
+/* Adapted for VeraCrypt */
+
+#ifndef _SHA2_SMALL_H
+#define _SHA2_SMALL_H
+
+#include "Common/Tcdefs.h"
+#include "Common/Endian.h"
+
+#define SHA256_DIGEST_SIZE  32
+#define SHA256_BLOCK_SIZE   64
+
+#define VOID_RETURN	void
+#define INT_RETURN	int
+
+#if defined(__cplusplus)
+extern "C"
+{
+#endif
+
+typedef struct {
+
+	uint32		highLength;
+	uint32		lowLength;
+	uint32		state[8];
+	unsigned int curlen;
+	unsigned char buf[64];
+} sha256_ctx;
+
+/******************************************************************************/
+
+VOID_RETURN sha256_begin(sha256_ctx* ctx);
+VOID_RETURN sha256_hash(unsigned char* data, unsigned int len, sha256_ctx* ctx);
+VOID_RETURN sha256_end(unsigned char* hval, sha256_ctx* ctx);
+
+#if defined(__cplusplus)
+}
+#endif
+
+/******************************************************************************/
+
+#endif /* _h_PS_DIGEST */
+/******************************************************************************/
+