DataFlex

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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DataFlex

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoTunnel
    Variant vJson
    Handle hoJson
    Integer iSshPort
    Boolean iWaitForThreadExit
    String sTemp1

    Move False To iSuccess

    //  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.

    Get Create (RefClass(cComChilkatSshTunnel)) To hoTunnel
    If (Not(IsComObjectCreated(hoTunnel))) Begin
        Send CreateComObject of hoTunnel
    End

    //  List the allowed algorithms for each category, in order of preference.
    Get Create (RefClass(cComChilkatJsonObject)) To hoJson
    If (Not(IsComObjectCreated(hoJson))) Begin
        Send CreateComObject of hoJson
    End
    Get ComUpdateString Of hoJson "kex" "curve25519-sha256@libssh.org,ecdh-sha2-nistp256" To iSuccess
    Get ComUpdateString Of hoJson "hostKey" "ssh-ed25519,ecdsa-sha2-nistp256" To iSuccess
    Get ComUpdateString Of hoJson "cipher" "chacha20-poly1305@openssh.com,aes256-ctr" To iSuccess
    Get ComUpdateString Of hoJson "mac" "hmac-sha2-256,hmac-sha2-512" To iSuccess

    //  Apply the allow-list before connecting.
    Get pvComObject of hoJson to vJson
    Get ComSetAllowedAlgorithms Of hoTunnel vJson To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoTunnel To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Set ComDestHostname Of hoTunnel To "db.internal.example.com"
    Set ComDestPort Of hoTunnel To 5432

    Move 22 To iSshPort
    Get ComConnect Of hoTunnel "ssh.example.com" iSshPort To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoTunnel To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Showln "Connected."

    Move True To iWaitForThreadExit
    Get ComCloseTunnel Of hoTunnel iWaitForThreadExit To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoTunnel To sTemp1
        Showln sTemp1
        Procedure_Return
    End



End_Procedure