Squashed commit upgrading to mbedtls-2.16.5

Squash merging branch import/mbedtls-2.16.5

058aefb2bfa4 ("core: mbedtls: use SHA-256 crypto accelerated routines")
bcef9baed8f1 ("core: mbedtls: use SHA-1 crypto accelerated routines")
c9359f31db12 ("core: mbedtls: use AES crypto accelerated routines")
0e6c1e2642c7 ("core: merge tee_*_get_digest_size() into a single function")
0cb3c28a2f4d ("libmbedtls: mbedtls_mpi_exp_mod(): optimize mempool usage")
5abf0e6ab72e ("libmbedtls: mbedtls_mpi_exp_mod(): reduce stack usage")
2ccc08ac7fef ("libmbedtls: preserve mempool usage on reinit")
cd2a24648569 ("libmbedtls: mbedtls_mpi_exp_mod() initialize W")
7727182ecb56 ("libmbedtls: fix no CRT issue")
120737075dcf ("libmbedtls: add interfaces in mbedtls for context memory operation")
1126250b3af8 ("libmbedtls: add missing source file chachapoly.c")
23972e9f1c98 ("libmedtls: mpi_miller_rabin: increase count limit")
1fcbc05b3cd2 ("libmbedtls: add mbedtls_mpi_init_mempool()")
66e03f068078 ("libmbedtls: make mbedtls_mpi_mont*() available")
d07e0ce56236 ("libmbedtls: refine mbedtls license header")
491ee2cd0ff4 ("mbedtls: configure mbedtls to reach for config")
9b6cee685d9a ("mbedtls: remove default include/mbedtls/config.h")
84f7467a0a91 ("Import mbedtls-2.16.5")

Signed-off-by: Jerome Forissier <jerome@forissier.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/lib/libmbedtls/mbedtls/library/pkwrite.c b/lib/libmbedtls/mbedtls/library/pkwrite.c
index c3e9721..eff9e67 100644
--- a/lib/libmbedtls/mbedtls/library/pkwrite.c
+++ b/lib/libmbedtls/mbedtls/library/pkwrite.c
@@ -38,7 +38,9 @@
 #include "mbedtls/rsa.h"
 #endif
 #if defined(MBEDTLS_ECP_C)
+#include "mbedtls/bignum.h"
 #include "mbedtls/ecp.h"
+#include "mbedtls/platform_util.h"
 #endif
 #if defined(MBEDTLS_ECDSA_C)
 #include "mbedtls/ecdsa.h"
@@ -150,6 +152,26 @@
 
     return( (int) len );
 }
+
+/*
+ * privateKey  OCTET STRING -- always of length ceil(log2(n)/8)
+ */
+static int pk_write_ec_private( unsigned char **p, unsigned char *start,
+                                mbedtls_ecp_keypair *ec )
+{
+    int ret;
+    size_t byte_length = ( ec->grp.pbits + 7 ) / 8;
+    unsigned char tmp[MBEDTLS_ECP_MAX_BYTES];
+
+    ret = mbedtls_mpi_write_binary( &ec->d, tmp, byte_length );
+    if( ret != 0 )
+        goto exit;
+    ret = mbedtls_asn1_write_octet_string( p, start, tmp, byte_length );
+
+exit:
+    mbedtls_platform_zeroize( tmp, byte_length );
+    return( ret );
+}
 #endif /* MBEDTLS_ECP_C */
 
 int mbedtls_pk_write_pubkey( unsigned char **p, unsigned char *start,
@@ -364,9 +386,8 @@
                             MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED | 0 ) );
         len += par_len;
 
-        /* privateKey: write as MPI then fix tag */
-        MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_mpi( &c, buf, &ec->d ) );
-        *c = MBEDTLS_ASN1_OCTET_STRING;
+        /* privateKey */
+        MBEDTLS_ASN1_CHK_ADD( len, pk_write_ec_private( &c, buf, ec ) );
 
         /* version */
         MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_int( &c, buf, 1 ) );