diff --git a/tests/scripts/mbedtls_test.py b/tests/scripts/mbedtls_test.py
index 7e1cebf7d..62c229631 100755
--- a/tests/scripts/mbedtls_test.py
+++ b/tests/scripts/mbedtls_test.py
@@ -89,24 +89,20 @@ class TestDataParser(object):
         :param data_f: Data file object
         :return:
         """
-        while True:
-            line = data_f.readline().strip()
+        for line in data_f:
+            line = line.strip()
             if not line:
-                break
+                continue
             # Read test name
             name = line
 
             # Check dependencies
             dependencies = []
-            line = data_f.readline().strip()
-            if not line:
-                break
+            line = next(data_f).strip()
             match = re.search('depends_on:(.*)', line)
             if match:
                 dependencies = [int(x) for x in match.group(1).split(':')]
-                line = data_f.readline().strip()
-                if not line:
-                    break
+                line = next(data_f).strip()
 
             # Read test vectors
             line = line.replace('\\n', '\n')
@@ -265,20 +261,20 @@ class MbedTlsTest(BaseHostTest):
         for typ, param in parameters:
             if typ == 'int' or typ == 'exp':
                 i = int(param)
-                data_bytes += 'I' if typ == 'int' else 'E'
+                data_bytes += b'I' if typ == 'int' else b'E'
                 self.align_32bit(data_bytes)
                 data_bytes += self.int32_to_big_endian_bytes(i)
             elif typ == 'char*':
                 param = param.strip('"')
                 i = len(param) + 1  # + 1 for null termination
-                data_bytes += 'S'
+                data_bytes += b'S'
                 self.align_32bit(data_bytes)
                 data_bytes += self.int32_to_big_endian_bytes(i)
-                data_bytes += bytearray(list(param))
-                data_bytes += '\0'   # Null terminate
+                data_bytes += bytes(param, 'ascii')
+                data_bytes += b'\0'   # Null terminate
             elif typ == 'hex':
                 binary_data = self.hex_str_bytes(param)
-                data_bytes += 'H'
+                data_bytes += b'H'
                 self.align_32bit(data_bytes)
                 i = len(binary_data)
                 data_bytes += self.int32_to_big_endian_bytes(i)
@@ -313,7 +309,7 @@ class MbedTlsTest(BaseHostTest):
 
         param_bytes, length = self.test_vector_to_bytes(function_id,
                                                         dependencies, args)
-        self.send_kv(bytes(length).decode(), bytes(param_bytes).decode())
+        self.send_kv(length.hex(), param_bytes.hex())
 
     @staticmethod
     def get_result(value):
diff --git a/tests/suites/target_test.function b/tests/suites/target_test.function
index e4c3e30de..35255c9d6 100644
--- a/tests/suites/target_test.function
+++ b/tests/suites/target_test.function
@@ -59,10 +59,43 @@ int verify_dependencies( uint8_t count, uint8_t * dep_p )
     return( DEPENDENCY_SUPPORTED );
 }
 
+/**
+ * \brief       Receives hex string on serial interface, and converts to a byte.
+ *
+ * \param none
+ *
+ * \return      unsigned int8
+ */
+uint8_t receive_byte()
+{
+    uint8_t byte;
+    uint8_t c;
+
+    c = greentea_getc();
+    if( c >= '0' && c <= '9' )
+        c -= '0';
+    else if( c >= 'a' && c <= 'f' )
+        c = ( c -'a' ) + 10;
+    else if( c >= 'A' && c <= 'F' )
+        c = ( c - 'A' ) + 10;
+
+    byte = c * 0x10;
+
+    c = greentea_getc();
+    if( c >= '0' && c <= '9' )
+        c -= '0';
+    else if( c >= 'a' && c <= 'f' )
+        c = ( c -'a' ) + 10;
+    else if( c >= 'A' && c <= 'F' )
+        c = ( c - 'A' ) + 10;
+
+    byte += c ;
+    return( byte);
+}
 
 /**
  * \brief       Receives unsigned integer on serial interface.
- *              Integers are encoded in network order.
+ *              Integers are encoded in network order, and sent as hex ascii string.
  *
  * \param none
  *
@@ -71,10 +104,10 @@ int verify_dependencies( uint8_t count, uint8_t * dep_p )
 uint32_t receive_uint32()
 {
     uint32_t value;
-    value =  (uint8_t)greentea_getc() << 24;
-    value |= (uint8_t)greentea_getc() << 16;
-    value |= (uint8_t)greentea_getc() << 8;
-    value |= (uint8_t)greentea_getc();
+    value =  receive_byte() << 24;
+    value |= receive_byte() << 16;
+    value |= receive_byte() << 8;
+    value |= receive_byte();
     return( (uint32_t)value );
 }
 
@@ -132,7 +165,7 @@ uint8_t * receive_data( uint32_t * data_len )
     greentea_getc(); // read ';' received after key i.e. *data_len
 
     for( i = 0; i < *data_len; i++ )
-        data[i] = greentea_getc();
+        data[i] = receive_byte();
 
     /* Read closing braces */
     for( i = 0; i < 2; i++ )