Objective-C

SSH Tunnel Set Allowed SSH Algorithms

Demonstrates the Chilkat SshTunnel.SetAllowedAlgorithms method, which restricts the SSH connection to a specific set of algorithms. A JsonObject supplies comma-separated allow-lists for the kex, hostKey, cipher, and mac categories. It must be called before Connect.

Important: You typically should not set allowed algorithms explicitly. By default Chilkat orders algorithms according to best practices and accounts for known vulnerabilities.

Background: SSH negotiates a mutually supported algorithm from each category at connection time, and pinning that choice makes an application brittle: if the server later drops a weak algorithm, the two sides may fail to agree and the tunnel stops working. The legitimate reasons to override are a security policy mandating specific algorithms or a compatibility problem with an old server; otherwise let the library's defaults evolve with current guidance.

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Objective-C

#import <CkoSshTunnel.h>
#import <CkoJsonObject.h>

BOOL success = NO;

//  Demonstrates the SshTunnel.SetAllowedAlgorithms method, which restricts the SSH connection to a
//  specific set of algorithms.  The only argument is a JsonObject.  It must be called before
//  Connect.
//  
//  Note: You typically should NOT set allowed algorithms explicitly.  By default Chilkat orders
//  algorithms according to best practices and accounts for known vulnerabilities.  Hard-coding
//  them can make an application brittle if a server later changes its allowed algorithms.

CkoSshTunnel *tunnel = [[CkoSshTunnel alloc] init];

//  List the allowed algorithms for each category, in order of preference.
CkoJsonObject *json = [[CkoJsonObject alloc] init];
[json UpdateString: @"kex" value: @"curve25519-sha256@libssh.org,ecdh-sha2-nistp256"];
[json UpdateString: @"hostKey" value: @"ssh-ed25519,ecdsa-sha2-nistp256"];
[json UpdateString: @"cipher" value: @"chacha20-poly1305@openssh.com,aes256-ctr"];
[json UpdateString: @"mac" value: @"hmac-sha2-256,hmac-sha2-512"];

//  Apply the allow-list before connecting.
success = [tunnel SetAllowedAlgorithms: json];
if (success == NO) {
    NSLog(@"%@",tunnel.LastErrorText);
    return;
}

tunnel.DestHostname = @"db.internal.example.com";
tunnel.DestPort = [NSNumber numberWithInt:5432];

int sshPort = 22;
success = [tunnel Connect: @"ssh.example.com" port: [NSNumber numberWithInt: sshPort]];
if (success == NO) {
    NSLog(@"%@",tunnel.LastErrorText);
    return;
}

NSLog(@"%@",@"Connected.");

BOOL waitForThreadExit = YES;
success = [tunnel CloseTunnel: waitForThreadExit];
if (success == NO) {
    NSLog(@"%@",tunnel.LastErrorText);
    return;
}