Lua

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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Lua

local chilkat = require("chilkat")

-- 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.

local tunnel = chilkat.SshTunnel.new()

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

-- Apply the allow-list before connecting.
local success = tunnel:set_allowed_algorithms(json)
if not success then
    print(tunnel.last_error_text)
    return
end

tunnel.dest_hostname = "db.internal.example.com"
tunnel.dest_port = 5432

local sshPort = 22
success = tunnel:connect("ssh.example.com", sshPort)
if not success then
    print(tunnel.last_error_text)
    return
end

print("Connected.")

local waitForThreadExit = true
success = tunnel:close_tunnel(waitForThreadExit)
if not success then
    print(tunnel.last_error_text)
    return
end