(Tcl) SSH Set Allowed Algorithms

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Demonstrates how to explicitly set the algorithms allowed in the SSH connection protocol.

Note: This example requires Chilkat v9.5.0.99 or greater.

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load ./chilkat.dll

# This example requires the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

set ssh [new_CkSsh]

set json [new_CkJsonObject]

# Here are the algorithms supported by Chilkat at the time this example was written (14-June-2024)

# ---------------------------
# SSH Key-Exchange Algorithms
# ---------------------------
# curve25519-sha256
# curve25519-sha256@libssh.org
# ecdh-sha2-nistp256
# ecdh-sha2-nistp384
# ecdh-sha2-nistp521
# diffie-hellman-group14-sha256
# diffie-hellman-group16-sha512
# diffie-hellman-group18-sha512
# diffie-hellman-group-exchange-sha256
# diffie-hellman-group1-sha1
# diffie-hellman-group14-sha1
# diffie-hellman-group-exchange-sha1

# ---------------------------
# SSH Host Key Algorithms
# ---------------------------
# ssh-ed25519
# ecdsa-sha2-nistp256
# ecdsa-sha2-nistp384
# ecdsa-sha2-nistp521
# rsa-sha2-256
# rsa-sha2-512
# ssh-rsa
# ssh-dss

# ---------------------------
# SSH Cipher Algorithms
# ---------------------------
# chacha20-poly1305@openssh.com
# aes128-ctr
# aes256-ctr
# aes192-ctr
# aes128-cbc
# aes256-cbc
# aes192-cbc
# aes128-gcm@openssh.com
# aes256-gcm@openssh.com
# twofish256-cbc
# twofish128-cbc
# blowfish-cbc

# ---------------------------
# SSH MAC Algorithms
# ---------------------------
# hmac-sha2-256
# hmac-sha2-512
# hmac-sha2-256-etm@openssh.com
# hmac-sha2-512-etm@openssh.com
# hmac-sha1-etm@openssh.com
# hmac-sha1
# hmac-ripemd160
# hmac-sha1-96
# hmac-md5

# Specify the allowed key-exchange, host-key, cipher (i.e. encryption), and mac (i.e. hash) algorithms allowed, in the order of preference.
# -------------------------------------------------------------------------------------------------------------------------------------------
# Note: You typically should NOT explicitly set allowed algorithms.
# By default, Chilkat orders algorithms according to best practices, and pays attention to vulnerabilities such as the "Terrapin Attack".
# Hard-coding algorthims can make your application brittle and prone to breaking over a long period of time,
# if a server (at some point in the future) changes its allowed algorithms, or if you connect to a different server,
# such that the client (Chilkat) and server cannot find a set of mutually agreed-upon algorithms.
# -------------------------------------------------------------------------------------------------------------------------------------------
set allowed_kex "curve25519-sha256@libssh.org,ecdh-sha2-nistp256"
set allowed_hostKey "ssh-ed25519,ecdsa-sha2-nistp256"
set allowed_cipher "chacha20-poly1305@openssh.com,aes256-ctr"
set allowed_mac "hmac-sha2-256,hmac-sha2-512"

CkJsonObject_UpdateString $json "kex" $allowed_kex
CkJsonObject_UpdateString $json "hostKey" $allowed_hostKey
CkJsonObject_UpdateString $json "cipher" $allowed_cipher
CkJsonObject_UpdateString $json "mac" $allowed_mac
CkSsh_SetAllowedAlgorithms $ssh $json

set port 22
set success [CkSsh_Connect $ssh "example.com" $port]
if {$success != 1} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    delete_CkJsonObject $json
    exit
}

puts "Connected."

# ....
# ....

delete_CkSsh $ssh
delete_CkJsonObject $json