Delphi ActiveX

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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var
success: Integer;
tunnel: TChilkatSshTunnel;
json: TChilkatJsonObject;
sshPort: Integer;
waitForThreadExit: Integer;

begin
success := 0;

//  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.

tunnel := TChilkatSshTunnel.Create(Self);

//  List the allowed algorithms for each category, in order of preference.
json := TChilkatJsonObject.Create(Self);
json.UpdateString('kex','curve25519-sha256@libssh.org,ecdh-sha2-nistp256');
json.UpdateString('hostKey','ssh-ed25519,ecdsa-sha2-nistp256');
json.UpdateString('cipher','chacha20-poly1305@openssh.com,aes256-ctr');
json.UpdateString('mac','hmac-sha2-256,hmac-sha2-512');

//  Apply the allow-list before connecting.
success := tunnel.SetAllowedAlgorithms(json.ControlInterface);
if (success = 0) then
  begin
    Memo1.Lines.Add(tunnel.LastErrorText);
    Exit;
  end;

tunnel.DestHostname := 'db.internal.example.com';
tunnel.DestPort := 5432;

sshPort := 22;
success := tunnel.Connect('ssh.example.com',sshPort);
if (success = 0) then
  begin
    Memo1.Lines.Add(tunnel.LastErrorText);
    Exit;
  end;
Memo1.Lines.Add('Connected.');

waitForThreadExit := 1;
success := tunnel.CloseTunnel(waitForThreadExit);
if (success = 0) then
  begin
    Memo1.Lines.Add(tunnel.LastErrorText);
    Exit;
  end;