Add ASN.1 ENUMERATED tag support

Add ASN.1 ENUMERATED [1] tag to supported tag list.

1. https://tools.ietf.org/html/rfc3641#page-8

Signed-off-by: Mykhailo Sopiha <mykhailo.sopiha@linaro.org>
diff --git a/include/mbedtls/asn1.h b/include/mbedtls/asn1.h
index 1a76111..1c6683f 100644
--- a/include/mbedtls/asn1.h
+++ b/include/mbedtls/asn1.h
@@ -75,6 +75,7 @@
 #define MBEDTLS_ASN1_OCTET_STRING            0x04
 #define MBEDTLS_ASN1_NULL                    0x05
 #define MBEDTLS_ASN1_OID                     0x06
+#define MBEDTLS_ASN1_ENUMERATED              0x0A
 #define MBEDTLS_ASN1_UTF8_STRING             0x0C
 #define MBEDTLS_ASN1_SEQUENCE                0x10
 #define MBEDTLS_ASN1_SET                     0x11
@@ -254,14 +255,33 @@
  *              a valid ASN.1 INTEGER.
  * \return      #MBEDTLS_ERR_ASN1_INVALID_LENGTH if the parsed value does
  *              not fit in an \c int.
- * \return      An ASN.1 error code if the input does not start with
- *              a valid ASN.1 INTEGER.
  */
 int mbedtls_asn1_get_int( unsigned char **p,
                           const unsigned char *end,
                           int *val );
 
 /**
+ * \brief       Retrieve an enumerated ASN.1 tag and its value.
+ *              Updates the pointer to immediately behind the full tag.
+ *
+ * \param p     On entry, \c *p points to the start of the ASN.1 element.
+ *              On successful completion, \c *p points to the first byte
+ *              beyond the ASN.1 element.
+ *              On error, the value of \c *p is undefined.
+ * \param end   End of data.
+ * \param val   On success, the parsed value.
+ *
+ * \return      0 if successful.
+ * \return      An ASN.1 error code if the input does not start with
+ *              a valid ASN.1 ENUMERATED.
+ * \return      #MBEDTLS_ERR_ASN1_INVALID_LENGTH if the parsed value does
+ *              not fit in an \c int.
+ */
+int mbedtls_asn1_get_enum( unsigned char **p,
+                           const unsigned char *end,
+                           int *val );
+
+/**
  * \brief       Retrieve a bitstring ASN.1 tag and its value.
  *              Updates the pointer to immediately behind the full tag.
  *
@@ -367,8 +387,6 @@
  * \return      #MBEDTLS_ERR_ASN1_INVALID_LENGTH if the parsed value does
  *              not fit in an \c int.
  * \return      An MPI error code if the parsed value is too large.
- * \return      An ASN.1 error code if the input does not start with
- *              a valid ASN.1 INTEGER.
  */
 int mbedtls_asn1_get_mpi( unsigned char **p,
                           const unsigned char *end,
diff --git a/include/mbedtls/asn1write.h b/include/mbedtls/asn1write.h
index 9824146..0bce28e 100644
--- a/include/mbedtls/asn1write.h
+++ b/include/mbedtls/asn1write.h
@@ -193,6 +193,21 @@
 int mbedtls_asn1_write_int( unsigned char **p, unsigned char *start, int val );
 
 /**
+ * \brief           Write an enum tag (#MBEDTLS_ASN1_ENUMERATED) and value
+ *                  in ASN.1 format.
+ *
+ * \note            This function works backwards in data buffer.
+ *
+ * \param p         The reference to the current position pointer.
+ * \param start     The start of the buffer, for bounds-checking.
+ * \param val       The integer value to write.
+ *
+ * \return          The number of bytes written to \p p on success.
+ * \return          A negative \c MBEDTLS_ERR_ASN1_XXX error code on failure.
+ */
+int mbedtls_asn1_write_enum( unsigned char **p, unsigned char *start, int val );
+
+/**
  * \brief           Write a string in ASN.1 format using a specific
  *                  string encoding tag.