next up previous contents
: Local extension on server : Projects in work in : Projects in work in   ܼ

OX DATA with Length

OX_DATA_WITH_LENGTH is the OX tag for OX data message with a digital signature. It is followed by the serial number, CMO, an end mark and a digital signature. This type of OX data message is called secured OX DATA.

#define OX_SECURED_DATA               521

int32 OX_DATA_WITH_LENGTH int32 serial int32 size CMObject o tail

If size is equal to -1, then it is ignored.

tail is defined as follows.
int32 CMO_START_SIGNATURE int32 size signature

Here size is the length of signature. signature is a digital signature of CMO data by a Hash function and is used to detect invalid serialized objects. If size of Tail is equal to 0, then it has no digital signature.

Currently there are four modes of communicating data.

  1. Only OX_DATA is used with checking by mathcap.
  2. Only OX_SECURED_DATA is used.
  3. Both OX_DATA and OX_SECURED_DATA can be used.
  4. Only OX_DATA is used without checking by mathcap.

Suppose that the mathcap handling is incomplete and an application has received unknown CMObject. In mode 1, the application cannot detect the end of the CMObject and it will not be able to understand the subsequent messages. In mode 2, the application can detect the end of the unknown CMObject from the size information. However, in mode 2, additional cost is required on the sender to compute the total length of CMObjects.

Note that the exchange of mathcaps are not necessary at the start of a session. Any server should be implemented so that it can change the communication mode dynamically, say, from 4 to 1.


next up previous contents
: Local extension on server : Projects in work in : Projects in work in   ܼ
Nobuki Takayama Heisei 28.8.27.