SSH Client

SSH Minimal Client Example

Overview

This NetBurner application demonstrates a minimal SSH client implementation that connects to an SSH server and reads data continuously until the connection is closed. The client establishes an encrypted SSH connection and can be used as a foundation for building more complex SSH-based applications.

Features

• Establishes SSH connection to a remote server
• User authentication with password
• Continuous data reading from SSH server
• Automatic reconnection on connection failure
• Built-in diagnostics and logging
• Certificate and key generation support

Configuration

Server Settings

The application is configured to connect to an SSH server using the following constants in main.cpp:

#define SSH_SERVER_NAME "10.1.1.131"    // Target SSH server IP address
#define SSH_REMOTE_PORT 22              // SSH server port (standard port 22)
#define CONNECTION_TIMEOUT 120          // Connection timeout in seconds

Authentication

The application uses password-based authentication with these default credentials:

• Username: "guest" (specified in SshConnect call)
• Password: "TestPassword" (set in ClientUserAuth function)

Hardware Requirements

• NetBurner device with network connectivity
• Active network connection (DHCP or static IP)
• USB or Serial connection for monitoring

Setup Instructions

1. Configure Target Server
   • Update SSH_SERVER_NAME with your SSH server's IP address
   • Ensure the SSH server is running and accessible on port 22
   • Verify firewall settings allow SSH connections
2. Compile and Deploy
   • Compile the application using NetBurner development tools
   • Load the compiled firmware onto your NetBurner device
3. Monitor Operation
   • Connect to the device using MTTTY via USB or Serial port
   • View connection status and received data in the terminal

Code Structure

Main Components

• UserMain(): Primary application entry point
  • Initializes system components
  • Configures SSH client settings
  • Manages connection loop
• ClientUserAuth(): Authentication callback
  • Called when server requests user credentials
  • Returns username and password for authentication

Key Functions

• NbSshInit(): Initializes SSH subsystem
• SshConnect(): Establishes SSH connection to server
• ReadWithTimeout(): Reads data from SSH connection with timeout
• EnableOnboardCertificateCreation(): Enables automatic certificate generation

Operation Flow

1. System initialization and network setup
2. SSH subsystem initialization
3. Connection attempt to configured server
4. User authentication when prompted
5. Continuous data reading loop
6. Connection monitoring and automatic reconnection

Buffer Configuration

The application uses a 4KB receive buffer:

#define RX_BUFSIZE (4096)
char RXBuffer[RX_BUFSIZE];

Task Stack

SSH operations use an extended stack size:

#define SSHSERVER_TASK_STACK_SIZE (USER_TASK_STK_SIZE * 4)

Troubleshooting

Common Issues

• Connection Failed: Verify server IP address and network connectivity
• Authentication Failed: Check username/password credentials
• Network Timeout: Ensure DHCP is working or configure static IP
• Certificate Errors: Verify certificate generation is enabled

Debug Output

The application provides detailed logging including:

• SSH initialization status
• Connection attempts and results
• Data received from server
• Connection closure notifications

Customization

Modifying Authentication

Update the ClientUserAuth() function to implement different authentication methods:

int ClientUserAuth(const NBString &usernamePtr, NBString &passwordPtr)
{
    // Custom authentication logic here
    passwordPtr = "YourPassword";
    return 1; // Return 1 for success, 0 for failure
}

Adding Data Processing

Extend the data reading loop in UserMain() to process received data:

if (n != 0)
{
    printf("Read %d bytes: %s\n", n, RXBuffer);
    // Add custom data processing here
}

Dependencies

• NetBurner SSH library (ssh/NetBurner/NbWolfSsh.h)
• Certificate generation support (crypto/certgen.h)
• Standard NetBurner system libraries

Notes

• The application includes system diagnostics which should be disabled for production use
• Automatic certificate creation is enabled for SSL/TLS support
• The client will continuously attempt to reconnect if the connection is lost
• All received data is null-terminated and printed to the console