SecLink Terminal Demo

DOS terminal emulator combining the DVX windowed GUI with SecLink encrypted serial communication. Connects to a remote BBS through the SecLink proxy, providing a full ANSI terminal in a DVX-style window with encrypted transport.

Architecture

termdemo (DOS, 86Box)
    |
    +--- DVX GUI          windowed desktop, ANSI terminal widget
    |
    +--- SecLink            encrypted serial link
    |      |
    |      +--- packet      HDLC framing, CRC, retransmit
    |      +--- security    DH key exchange, XTEA-CTR cipher
    |      +--- rs232       ISR-driven UART I/O
    |
  COM port (86Box emulated modem)
    |
  TCP:2323
    |
  secproxy (Linux)
    |
  TCP:23
    |
  Remote BBS

All traffic between the terminal and the proxy is encrypted via XTEA-CTR on SecLink channel 0. The proxy decrypts and forwards plaintext to the BBS over telnet.

Usage

termdemo [com_port] [baud_rate]

Argument	Default	Description
`com_port`	1	COM port number (1-4)
`baud_rate`	115200	Serial baud rate

termdemo                  # COM1 at 115200
termdemo 2                # COM2 at 115200
termdemo 1 57600          # COM1 at 57600
termdemo -h               # show usage

Startup Sequence

Seed the RNG from hardware entropy
Open SecLink on the specified COM port (8N1, no handshake)
Perform DH key exchange (blocks until the proxy completes its side)
Initialize the DVX GUI (1024x768, 16bpp VESA)
Create a resizable terminal window with menu bar and status bar
Enter the main loop

The handshake completes in text mode before the GUI starts, so the DOS console shows progress messages during connection setup.

Main Loop

Each iteration:

dvxUpdate() -- process mouse, keyboard, paint, and window events
secLinkPoll() -- read serial data, decrypt, deliver to ring buffer
wgtAnsiTermPoll() -- drain ring buffer into the ANSI parser

Data Flow

BBS -> proxy -> serial -> secLinkPoll() -> onRecv() -> ring buffer
    -> commRead() -> wgtAnsiTermWrite() -> ANSI parser -> screen

Keyboard -> widgetAnsiTermOnKey() -> commWrite()
    -> secLinkSend() -> serial -> proxy -> BBS

A 4KB ring buffer bridges the SecLink receive callback (which fires during secLinkPoll()) and the terminal widget's comm read interface (which is polled by wgtAnsiTermPoll()).

GUI

Window: resizable, titled "SecLink Terminal"
Menu bar: File -> Quit
Terminal: 80x25 ANSI terminal widget with 1000-line scrollback
Status bar: shows COM port, baud rate, and encryption status

The ANSI terminal widget supports standard escape sequences including cursor control, SGR colors (16-color CGA palette), erase, scroll, insert/delete lines, and DEC private modes (cursor visibility, line wrap).

Test Setup

Start the SecLink proxy on the Linux host:
```
secproxy 2323 bbs.example.com 23
```
Configure 86Box with a COM port pointing at the proxy's listen port (TCP client mode, port 2323, no telnet negotiation)
Run the terminal inside 86Box:
```
termdemo
```
The handshake completes, the GUI appears, and BBS output is displayed in the terminal window

Building

make        # builds ../bin/termdemo.exe
make clean  # removes objects and binary

The Makefile builds all dependency libraries automatically. Objects are placed in ../obj/termdemo/, the binary in ../bin/.

Dependencies

All libraries are in ../lib/:

Library	Purpose
`libdvx.a`	DVX windowed GUI and widget system
`libseclink.a`	Secure serial link wrapper
`libpacket.a`	HDLC framing and reliability
`libsecurity.a`	DH key exchange and XTEA cipher
`librs232.a`	ISR-driven UART serial driver

Target: DJGPP cross-compiler, 486+ CPU, VESA VBE 2.0+ video.

Files

termdemo/
  termdemo.c       terminal emulator program
  Makefile         DJGPP cross-compilation build

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