Added mechanism to provide alternative cipher / hash implementations

All symmetric cipher algorithms and hash algorithms now include support
for a POLARSSL_XXX_ALT flag that prevents the definition of the
algorithm context structure and all 'core' functions.

include/polarssl/sha2.h

@@ -3,7 +3,7 @@
  *
  * \brief SHA-224 and SHA-256 cryptographic hash function
  *
- *  Copyright (C) 2006-2010, Brainspark B.V.
+ *  Copyright (C) 2006-2013, Brainspark B.V.
  *
  *  This file is part of PolarSSL (http://www.polarssl.org)
  *  Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
@@ -27,6 +27,8 @@
 #ifndef POLARSSL_SHA2_H
 #define POLARSSL_SHA2_H
 
+#include "config.h"
+
 #include <string.h>
 
 #ifdef _MSC_VER
@@ -38,6 +40,10 @@ typedef UINT32 uint32_t;
 
 #define POLARSSL_ERR_SHA2_FILE_IO_ERROR                -0x0078  /**< Read/write error in file. */
 
+#if !defined(POLARSSL_SHA2_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          SHA-256 context structure
  */
@@ -82,6 +88,21 @@ void sha2_update( sha2_context *ctx, const unsigned char *input, size_t ilen );
  */
 void sha2_finish( sha2_context *ctx, unsigned char output[32] );
 
+/* Internal use */
+void sha2_process( sha2_context *ctx, const unsigned char data[64] );
+
+#ifdef __cplusplus
+}
+#endif
+
+#else  /* POLARSSL_SHA2_ALT */
+#include "sha2_alt.h"
+#endif /* POLARSSL_SHA2_ALT */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /**
  * \brief          Output = SHA-256( input buffer )
  *
@@ -160,9 +181,6 @@ void sha2_hmac( const unsigned char *key, size_t keylen,
  */
 int sha2_self_test( int verbose );
 
-/* Internal use */
-void sha2_process( sha2_context *ctx, const unsigned char data[64] );
-
 #ifdef __cplusplus
 }
 #endif