diff --git a/ChangeLog b/ChangeLog
index aaf34fcef9..4249de7666 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -135,6 +135,9 @@ Changes
    * Clarify the documentation of mbedtls_ssl_setup.
    * Use (void) when defining functions with no parameters. Contributed by
      Joris Aerts. #678
+   * Put the Cryptographic API outside of the XXX_ALT macro check, so
+     alternative header file will not need to redefined the same API,
+     and to force alternative implementer to use the same API.
 
 = mbed TLS 2.7.0 branch released 2018-02-03
 
diff --git a/include/mbedtls/aes.h b/include/mbedtls/aes.h
index 46016dcb7f..9043ddac41 100644
--- a/include/mbedtls/aes.h
+++ b/include/mbedtls/aes.h
@@ -59,14 +59,14 @@
 #define inline __inline
 #endif
 
-#if !defined(MBEDTLS_AES_ALT)
-// Regular implementation
-//
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_AES_ALT)
+// Regular implementation
+//
+
 /**
  * \brief The AES context-type definition.
  */
@@ -85,6 +85,10 @@ typedef struct
 }
 mbedtls_aes_context;
 
+#else  /* MBEDTLS_AES_ALT */
+#include "aes_alt.h"
+#endif /* MBEDTLS_AES_ALT */
+
 /**
  * \brief          This function initializes the specified AES context.
  *
@@ -391,18 +395,6 @@ MBEDTLS_DEPRECATED void mbedtls_aes_decrypt( mbedtls_aes_context *ctx,
 #undef MBEDTLS_DEPRECATED
 #endif /* !MBEDTLS_DEPRECATED_REMOVED */
 
-#ifdef __cplusplus
-}
-#endif
-
-#else  /* MBEDTLS_AES_ALT */
-#include "aes_alt.h"
-#endif /* MBEDTLS_AES_ALT */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /**
  * \brief          Checkup routine.
  *
diff --git a/include/mbedtls/arc4.h b/include/mbedtls/arc4.h
index f9d93f822f..f11fc5be0a 100644
--- a/include/mbedtls/arc4.h
+++ b/include/mbedtls/arc4.h
@@ -38,14 +38,14 @@
 
 #define MBEDTLS_ERR_ARC4_HW_ACCEL_FAILED                  -0x0019  /**< ARC4 hardware accelerator failed. */
 
-#if !defined(MBEDTLS_ARC4_ALT)
-// Regular implementation
-//
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_ARC4_ALT)
+// Regular implementation
+//
+
 /**
  * \brief     ARC4 context structure
  *
@@ -61,6 +61,10 @@ typedef struct
 }
 mbedtls_arc4_context;
 
+#else  /* MBEDTLS_ARC4_ALT */
+#include "arc4_alt.h"
+#endif /* MBEDTLS_ARC4_ALT */
+
 /**
  * \brief          Initialize ARC4 context
  *
@@ -118,18 +122,6 @@ void mbedtls_arc4_setup( mbedtls_arc4_context *ctx, const unsigned char *key,
 int mbedtls_arc4_crypt( mbedtls_arc4_context *ctx, size_t length, const unsigned char *input,
                 unsigned char *output );
 
-#ifdef __cplusplus
-}
-#endif
-
-#else  /* MBEDTLS_ARC4_ALT */
-#include "arc4_alt.h"
-#endif /* MBEDTLS_ARC4_ALT */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /**
  * \brief          Checkup routine
  *
diff --git a/include/mbedtls/blowfish.h b/include/mbedtls/blowfish.h
index c0ef5a04cc..22479be5ae 100644
--- a/include/mbedtls/blowfish.h
+++ b/include/mbedtls/blowfish.h
@@ -44,14 +44,14 @@
 #define MBEDTLS_ERR_BLOWFISH_HW_ACCEL_FAILED                   -0x0017  /**< Blowfish hardware accelerator failed. */
 #define MBEDTLS_ERR_BLOWFISH_INVALID_INPUT_LENGTH              -0x0018  /**< Invalid data input length. */
 
-#if !defined(MBEDTLS_BLOWFISH_ALT)
-// Regular implementation
-//
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_BLOWFISH_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          Blowfish context structure
  */
@@ -62,6 +62,10 @@ typedef struct
 }
 mbedtls_blowfish_context;
 
+#else  /* MBEDTLS_BLOWFISH_ALT */
+#include "blowfish_alt.h"
+#endif /* MBEDTLS_BLOWFISH_ALT */
+
 /**
  * \brief          Initialize Blowfish context
  *
@@ -198,8 +202,4 @@ int mbedtls_blowfish_crypt_ctr( mbedtls_blowfish_context *ctx,
 }
 #endif
 
-#else  /* MBEDTLS_BLOWFISH_ALT */
-#include "blowfish_alt.h"
-#endif /* MBEDTLS_BLOWFISH_ALT */
-
 #endif /* blowfish.h */
diff --git a/include/mbedtls/camellia.h b/include/mbedtls/camellia.h
index cf07629d9b..f0466bfd7e 100644
--- a/include/mbedtls/camellia.h
+++ b/include/mbedtls/camellia.h
@@ -40,14 +40,14 @@
 #define MBEDTLS_ERR_CAMELLIA_INVALID_INPUT_LENGTH         -0x0026  /**< Invalid data input length. */
 #define MBEDTLS_ERR_CAMELLIA_HW_ACCEL_FAILED              -0x0027  /**< Camellia hardware accelerator failed. */
 
-#if !defined(MBEDTLS_CAMELLIA_ALT)
-// Regular implementation
-//
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_CAMELLIA_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          CAMELLIA context structure
  */
@@ -58,6 +58,10 @@ typedef struct
 }
 mbedtls_camellia_context;
 
+#else  /* MBEDTLS_CAMELLIA_ALT */
+#include "camellia_alt.h"
+#endif /* MBEDTLS_CAMELLIA_ALT */
+
 /**
  * \brief          Initialize CAMELLIA context
  *
@@ -211,18 +215,6 @@ int mbedtls_camellia_crypt_ctr( mbedtls_camellia_context *ctx,
                        unsigned char *output );
 #endif /* MBEDTLS_CIPHER_MODE_CTR */
 
-#ifdef __cplusplus
-}
-#endif
-
-#else  /* MBEDTLS_CAMELLIA_ALT */
-#include "camellia_alt.h"
-#endif /* MBEDTLS_CAMELLIA_ALT */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /**
  * \brief          Checkup routine
  *
diff --git a/include/mbedtls/des.h b/include/mbedtls/des.h
index 5a1a636522..b0a82df9b8 100644
--- a/include/mbedtls/des.h
+++ b/include/mbedtls/des.h
@@ -46,14 +46,14 @@
 
 #define MBEDTLS_DES_KEY_SIZE    8
 
-#if !defined(MBEDTLS_DES_ALT)
-// Regular implementation
-//
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_DES_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          DES context structure
  *
@@ -67,6 +67,10 @@ typedef struct
 }
 mbedtls_des_context;
 
+#else  /* MBEDTLS_DES_ALT */
+#include "des_alt.h"
+#endif /* MBEDTLS_DES_ALT */
+
 /**
  * \brief          Triple-DES context structure
  */
@@ -331,17 +335,6 @@ int mbedtls_des3_crypt_cbc( mbedtls_des3_context *ctx,
  */
 void mbedtls_des_setkey( uint32_t SK[32],
                          const unsigned char key[MBEDTLS_DES_KEY_SIZE] );
-#ifdef __cplusplus
-}
-#endif
-
-#else  /* MBEDTLS_DES_ALT */
-#include "des_alt.h"
-#endif /* MBEDTLS_DES_ALT */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
 
 /**
  * \brief          Checkup routine
diff --git a/include/mbedtls/md2.h b/include/mbedtls/md2.h
index 0fd8b5afcc..08e75b247b 100644
--- a/include/mbedtls/md2.h
+++ b/include/mbedtls/md2.h
@@ -39,14 +39,14 @@
 
 #define MBEDTLS_ERR_MD2_HW_ACCEL_FAILED                   -0x002B  /**< MD2 hardware accelerator failed */
 
-#if !defined(MBEDTLS_MD2_ALT)
-// Regular implementation
-//
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_MD2_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          MD2 context structure
  *
@@ -64,6 +64,10 @@ typedef struct
 }
 mbedtls_md2_context;
 
+#else  /* MBEDTLS_MD2_ALT */
+#include "md2_alt.h"
+#endif /* MBEDTLS_MD2_ALT */
+
 /**
  * \brief          Initialize MD2 context
  *
@@ -235,18 +239,6 @@ MBEDTLS_DEPRECATED void mbedtls_md2_process( mbedtls_md2_context *ctx );
 #undef MBEDTLS_DEPRECATED
 #endif /* !MBEDTLS_DEPRECATED_REMOVED */
 
-#ifdef __cplusplus
-}
-#endif
-
-#else  /* MBEDTLS_MD2_ALT */
-#include "md2_alt.h"
-#endif /* MBEDTLS_MD2_ALT */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /**
  * \brief          Output = MD2( input buffer )
  *
diff --git a/include/mbedtls/md4.h b/include/mbedtls/md4.h
index 23fa95e46a..8ee4e5cabf 100644
--- a/include/mbedtls/md4.h
+++ b/include/mbedtls/md4.h
@@ -40,14 +40,14 @@
 
 #define MBEDTLS_ERR_MD4_HW_ACCEL_FAILED                   -0x002D  /**< MD4 hardware accelerator failed */
 
-#if !defined(MBEDTLS_MD4_ALT)
-// Regular implementation
-//
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_MD4_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          MD4 context structure
  *
@@ -64,6 +64,10 @@ typedef struct
 }
 mbedtls_md4_context;
 
+#else  /* MBEDTLS_MD4_ALT */
+#include "md4_alt.h"
+#endif /* MBEDTLS_MD4_ALT */
+
 /**
  * \brief          Initialize MD4 context
  *
@@ -238,18 +242,6 @@ MBEDTLS_DEPRECATED void mbedtls_md4_process( mbedtls_md4_context *ctx,
 #undef MBEDTLS_DEPRECATED
 #endif /* !MBEDTLS_DEPRECATED_REMOVED */
 
-#ifdef __cplusplus
-}
-#endif
-
-#else  /* MBEDTLS_MD4_ALT */
-#include "md4_alt.h"
-#endif /* MBEDTLS_MD4_ALT */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /**
  * \brief          Output = MD4( input buffer )
  *
diff --git a/include/mbedtls/md5.h b/include/mbedtls/md5.h
index 06ea4c5d44..43ead4b747 100644
--- a/include/mbedtls/md5.h
+++ b/include/mbedtls/md5.h
@@ -39,14 +39,14 @@
 
 #define MBEDTLS_ERR_MD5_HW_ACCEL_FAILED                   -0x002F  /**< MD5 hardware accelerator failed */
 
-#if !defined(MBEDTLS_MD5_ALT)
-// Regular implementation
-//
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_MD5_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          MD5 context structure
  *
@@ -63,6 +63,10 @@ typedef struct
 }
 mbedtls_md5_context;
 
+#else  /* MBEDTLS_MD5_ALT */
+#include "md5_alt.h"
+#endif /* MBEDTLS_MD5_ALT */
+
 /**
  * \brief          Initialize MD5 context
  *
@@ -238,18 +242,6 @@ MBEDTLS_DEPRECATED void mbedtls_md5_process( mbedtls_md5_context *ctx,
 #undef MBEDTLS_DEPRECATED
 #endif /* !MBEDTLS_DEPRECATED_REMOVED */
 
-#ifdef __cplusplus
-}
-#endif
-
-#else  /* MBEDTLS_MD5_ALT */
-#include "md5_alt.h"
-#endif /* MBEDTLS_MD5_ALT */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /**
  * \brief          Output = MD5( input buffer )
  *
diff --git a/include/mbedtls/ripemd160.h b/include/mbedtls/ripemd160.h
index 3a8b50a621..a0dac0c360 100644
--- a/include/mbedtls/ripemd160.h
+++ b/include/mbedtls/ripemd160.h
@@ -35,14 +35,14 @@
 
 #define MBEDTLS_ERR_RIPEMD160_HW_ACCEL_FAILED             -0x0031  /**< RIPEMD160 hardware accelerator failed */
 
-#if !defined(MBEDTLS_RIPEMD160_ALT)
-// Regular implementation
-//
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_RIPEMD160_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          RIPEMD-160 context structure
  */
@@ -54,6 +54,10 @@ typedef struct
 }
 mbedtls_ripemd160_context;
 
+#else  /* MBEDTLS_RIPEMD160_ALT */
+#include "ripemd160.h"
+#endif /* MBEDTLS_RIPEMD160_ALT */
+
 /**
  * \brief          Initialize RIPEMD-160 context
  *
@@ -178,18 +182,6 @@ MBEDTLS_DEPRECATED void mbedtls_ripemd160_process(
 #undef MBEDTLS_DEPRECATED
 #endif /* !MBEDTLS_DEPRECATED_REMOVED */
 
-#ifdef __cplusplus
-}
-#endif
-
-#else  /* MBEDTLS_RIPEMD160_ALT */
-#include "ripemd160_alt.h"
-#endif /* MBEDTLS_RIPEMD160_ALT */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /**
  * \brief          Output = RIPEMD-160( input buffer )
  *
diff --git a/include/mbedtls/sha1.h b/include/mbedtls/sha1.h
index 05540cde12..5fd02d3c0c 100644
--- a/include/mbedtls/sha1.h
+++ b/include/mbedtls/sha1.h
@@ -39,14 +39,14 @@
 
 #define MBEDTLS_ERR_SHA1_HW_ACCEL_FAILED                  -0x0035  /**< SHA-1 hardware accelerator failed */
 
-#if !defined(MBEDTLS_SHA1_ALT)
-// Regular implementation
-//
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_SHA1_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          The SHA-1 context structure.
  *
@@ -63,6 +63,10 @@ typedef struct
 }
 mbedtls_sha1_context;
 
+#else  /* MBEDTLS_SHA1_ALT */
+#include "sha1_alt.h"
+#endif /* MBEDTLS_SHA1_ALT */
+
 /**
  * \brief          This function initializes a SHA-1 context.
  *
@@ -240,18 +244,6 @@ MBEDTLS_DEPRECATED void mbedtls_sha1_process( mbedtls_sha1_context *ctx,
 #undef MBEDTLS_DEPRECATED
 #endif /* !MBEDTLS_DEPRECATED_REMOVED */
 
-#ifdef __cplusplus
-}
-#endif
-
-#else  /* MBEDTLS_SHA1_ALT */
-#include "sha1_alt.h"
-#endif /* MBEDTLS_SHA1_ALT */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /**
  * \brief          This function calculates the SHA-1 checksum of a buffer.
  *
diff --git a/include/mbedtls/sha256.h b/include/mbedtls/sha256.h
index ffb16c277a..8d7a1f733e 100644
--- a/include/mbedtls/sha256.h
+++ b/include/mbedtls/sha256.h
@@ -35,14 +35,14 @@
 
 #define MBEDTLS_ERR_SHA256_HW_ACCEL_FAILED                -0x0037  /**< SHA-256 hardware accelerator failed */
 
-#if !defined(MBEDTLS_SHA256_ALT)
-// Regular implementation
-//
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_SHA256_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          The SHA-256 context structure.
  *
@@ -61,6 +61,10 @@ typedef struct
 }
 mbedtls_sha256_context;
 
+#else  /* MBEDTLS_SHA256_ALT */
+#include "sha256_alt.h"
+#endif /* MBEDTLS_SHA256_ALT */
+
 /**
  * \brief          This function initializes a SHA-256 context.
  *
@@ -196,17 +200,6 @@ MBEDTLS_DEPRECATED void mbedtls_sha256_process( mbedtls_sha256_context *ctx,
 
 #undef MBEDTLS_DEPRECATED
 #endif /* !MBEDTLS_DEPRECATED_REMOVED */
-#ifdef __cplusplus
-}
-#endif
-
-#else  /* MBEDTLS_SHA256_ALT */
-#include "sha256_alt.h"
-#endif /* MBEDTLS_SHA256_ALT */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
 
 /**
  * \brief          This function calculates the SHA-224 or SHA-256
diff --git a/include/mbedtls/sha512.h b/include/mbedtls/sha512.h
index 8404a2d599..c4eb5a93c7 100644
--- a/include/mbedtls/sha512.h
+++ b/include/mbedtls/sha512.h
@@ -35,14 +35,14 @@
 
 #define MBEDTLS_ERR_SHA512_HW_ACCEL_FAILED                -0x0039  /**< SHA-512 hardware accelerator failed */
 
-#if !defined(MBEDTLS_SHA512_ALT)
-// Regular implementation
-//
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_SHA512_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          The SHA-512 context structure.
  *
@@ -61,6 +61,10 @@ typedef struct
 }
 mbedtls_sha512_context;
 
+#else  /* MBEDTLS_SHA512_ALT */
+#include "sha512_alt.h"
+#endif /* MBEDTLS_SHA512_ALT */
+
 /**
  * \brief          This function initializes a SHA-512 context.
  *
@@ -198,18 +202,6 @@ MBEDTLS_DEPRECATED void mbedtls_sha512_process(
 #undef MBEDTLS_DEPRECATED
 #endif /* !MBEDTLS_DEPRECATED_REMOVED */
 
-#ifdef __cplusplus
-}
-#endif
-
-#else  /* MBEDTLS_SHA512_ALT */
-#include "sha512_alt.h"
-#endif /* MBEDTLS_SHA512_ALT */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /**
  * \brief          This function calculates the SHA-512 or SHA-384
  *                 checksum of a buffer.
diff --git a/include/mbedtls/xtea.h b/include/mbedtls/xtea.h
index 34ccee3c22..8df708a3a5 100644
--- a/include/mbedtls/xtea.h
+++ b/include/mbedtls/xtea.h
@@ -39,14 +39,14 @@
 #define MBEDTLS_ERR_XTEA_INVALID_INPUT_LENGTH             -0x0028  /**< The data input has an invalid length. */
 #define MBEDTLS_ERR_XTEA_HW_ACCEL_FAILED                  -0x0029  /**< XTEA hardware accelerator failed. */
 
-#if !defined(MBEDTLS_XTEA_ALT)
-// Regular implementation
-//
-
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#if !defined(MBEDTLS_XTEA_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          XTEA context structure
  */
@@ -56,6 +56,10 @@ typedef struct
 }
 mbedtls_xtea_context;
 
+#else  /* MBEDTLS_XTEA_ALT */
+#include "xtea_alt.h"
+#endif /* MBEDTLS_XTEA_ALT */
+
 /**
  * \brief          Initialize XTEA context
  *
@@ -115,18 +119,6 @@ int mbedtls_xtea_crypt_cbc( mbedtls_xtea_context *ctx,
                     unsigned char *output);
 #endif /* MBEDTLS_CIPHER_MODE_CBC */
 
-#ifdef __cplusplus
-}
-#endif
-
-#else  /* MBEDTLS_XTEA_ALT */
-#include "xtea_alt.h"
-#endif /* MBEDTLS_XTEA_ALT */
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /**
  * \brief          Checkup routine
  *