Xbase++

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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LOCAL nSuccess
LOCAL oTunnel
LOCAL oJson
LOCAL nSshPort
LOCAL nWaitForThreadExit

nSuccess := 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.

oTunnel := CreateObject("Chilkat.SshTunnel")

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

//  Apply the allow-list before connecting.
nSuccess := oTunnel:SetAllowedAlgorithms(oJson)
IF (nSuccess == 0)
    ? oTunnel:LastErrorText
    oTunnel:destroy()
    oJson:destroy()
    RETURN
ENDIF

oTunnel:DestHostname := "db.internal.example.com"
oTunnel:DestPort := 5432

nSshPort := 22
nSuccess := oTunnel:Connect("ssh.example.com", nSshPort)
IF (nSuccess == 0)
    ? oTunnel:LastErrorText
    oTunnel:destroy()
    oJson:destroy()
    RETURN
ENDIF

? "Connected."

nWaitForThreadExit := 1
nSuccess := oTunnel:CloseTunnel(nWaitForThreadExit)
IF (nSuccess == 0)
    ? oTunnel:LastErrorText
    oTunnel:destroy()
    oJson:destroy()
    RETURN
ENDIF

oTunnel:destroy()
oJson:destroy()