PureBasic

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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IncludeFile "CkSshTunnel.pb"
IncludeFile "CkJsonObject.pb"

Procedure ChilkatExample()

    success.i = 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.i = CkSshTunnel::ckCreate()
    If tunnel.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ;  List the allowed algorithms for each category, in order of preference.
    json.i = CkJsonObject::ckCreate()
    If json.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkJsonObject::ckUpdateString(json,"kex","curve25519-sha256@libssh.org,ecdh-sha2-nistp256")
    CkJsonObject::ckUpdateString(json,"hostKey","ssh-ed25519,ecdsa-sha2-nistp256")
    CkJsonObject::ckUpdateString(json,"cipher","chacha20-poly1305@openssh.com,aes256-ctr")
    CkJsonObject::ckUpdateString(json,"mac","hmac-sha2-256,hmac-sha2-512")

    ;  Apply the allow-list before connecting.
    success = CkSshTunnel::ckSetAllowedAlgorithms(tunnel,json)
    If success = 0
        Debug CkSshTunnel::ckLastErrorText(tunnel)
        CkSshTunnel::ckDispose(tunnel)
        CkJsonObject::ckDispose(json)
        ProcedureReturn
    EndIf

    CkSshTunnel::setCkDestHostname(tunnel, "db.internal.example.com")
    CkSshTunnel::setCkDestPort(tunnel, 5432)

    sshPort.i = 22
    success = CkSshTunnel::ckConnect(tunnel,"ssh.example.com",sshPort)
    If success = 0
        Debug CkSshTunnel::ckLastErrorText(tunnel)
        CkSshTunnel::ckDispose(tunnel)
        CkJsonObject::ckDispose(json)
        ProcedureReturn
    EndIf

    Debug "Connected."

    waitForThreadExit.i = 1
    success = CkSshTunnel::ckCloseTunnel(tunnel,waitForThreadExit)
    If success = 0
        Debug CkSshTunnel::ckLastErrorText(tunnel)
        CkSshTunnel::ckDispose(tunnel)
        CkJsonObject::ckDispose(json)
        ProcedureReturn
    EndIf



    CkSshTunnel::ckDispose(tunnel)
    CkJsonObject::ckDispose(json)


    ProcedureReturn
EndProcedure