Added parsing of v3 extension subject key identifier

ChangeLog

@@ -32,6 +32,7 @@ Features
      may be up to two bytes shorter. This allows the library to support all
      hash and signature sizes that comply with FIPS 186-4, including SHA-512
      with a 1024-bit key.
+   * Added parsing of x509 v3 extension subject key identifier.
 
 Bugfix
    * Fix wrong order of freeing in programs/ssl/ssl_server2 example

include/mbedtls/x509_crt.h

@@ -73,6 +73,8 @@ typedef struct mbedtls_x509_crt
     mbedtls_x509_buf issuer_id;         /**< Optional X.509 v2/v3 issuer unique identifier. */
     mbedtls_x509_buf subject_id;        /**< Optional X.509 v2/v3 subject unique identifier. */
     mbedtls_x509_buf v3_ext;            /**< Optional X.509 v3 extensions.  */
+    mbedtls_x509_buf subject_key_id;    /**< Optional X.509 v3 extension subject key identifier. */
+
     mbedtls_x509_sequence subject_alt_names;    /**< Optional list of Subject Alternative Names (Only dNSName supported). */
 
     int ext_types;              /**< Bit string containing detected and parsed extensions */

library/oid.c

@@ -278,6 +278,10 @@ static const oid_x509_ext_t oid_x509_ext[] =
         { ADD_LEN( MBEDTLS_OID_NS_CERT_TYPE ),         "id-netscape-certtype",     "Netscape Certificate Type" },
         MBEDTLS_X509_EXT_NS_CERT_TYPE,
     },
+    {
+        { ADD_LEN( MBEDTLS_OID_SUBJECT_KEY_IDENTIFIER ), "id-ce-subjectKeyIdentifier",           "Subject Key Identifier" }, 
+        MBEDTLS_X509_EXT_SUBJECT_KEY_IDENTIFIER,
+    },
     {
         { NULL, 0, NULL, NULL },
         0,

library/x509_crt.c

@@ -800,6 +800,21 @@ static int x509_get_crt_ext( unsigned char **p,
                 return( ret );
             break;
 
+        case MBEDTLS_X509_EXT_SUBJECT_KEY_IDENTIFIER:
+            if( ( ret = mbedtls_asn1_get_tag( p, end_ext_data, &len,
+                MBEDTLS_ASN1_OCTET_STRING ) ) != 0 )
+            {
+                return( ret );
+            }
+            else
+            {
+                crt->subject_key_id.len = len;
+                crt->subject_key_id.tag = MBEDTLS_ASN1_OCTET_STRING;
+                crt->subject_key_id.p = *p;
+                *p += len;
+            }
+            break;
+
         case MBEDTLS_X509_EXT_SUBJECT_ALT_NAME:
             /* Parse subject alt name */
             if( ( ret = x509_get_subject_alt_name( p, end_ext_octet,