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SSH Set Allowed Algorithms

Demonstrates explicitly setting the algorithms allowed during SSH connection negotiation. A JsonObject supplies comma-separated allow-lists for the kex, hostKey, cipher, and mac categories, in order of preference, and is applied before connecting.

Important: You typically should not set allowed algorithms explicitly. By default Chilkat orders algorithms according to best practices and accounts for known vulnerabilities such as the Terrapin attack.

Background: SSH negotiates a mutually supported algorithm from each category at connection time, and pinning that choice makes an application brittle: if a server later drops a weak algorithm, or you point the code at a different server, the two sides may fail to agree and the connection breaks. The legitimate reasons to override are a security policy mandating specific algorithms, or a compatibility problem with an old device. Otherwise the safer default is to let the library's ordering evolve as cryptographic guidance changes.

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Local $bSuccess = False

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

;  Demonstrates explicitly setting the algorithms allowed during SSH connection negotiation.
;  
;  -------------------------------------------------------------------------------------------
;  Note: You typically should NOT explicitly set allowed algorithms.
;  By default, Chilkat orders algorithms according to best practices and accounts for known
;  vulnerabilities such as the "Terrapin Attack".  Hard-coding algorithms makes an application
;  brittle over time: if a server later changes its allowed algorithms, or if you connect to a
;  different server, the client and server may fail to agree on a mutually supported set.
;  -------------------------------------------------------------------------------------------

$oSsh = ObjCreate("Chilkat.Ssh")

$oJson = ObjCreate("Chilkat.JsonObject")

;  Algorithms supported by Chilkat, by category:
;  
;  Key-exchange:  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
;  
;  Host key:  ssh-ed25519, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521,
;    rsa-sha2-256, rsa-sha2-512, ssh-rsa, ssh-dss
;  
;  Cipher:  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
;  
;  MAC:  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

;  List the allowed algorithms for each category, in order of preference.
Local $sAllowed_kex = "curve25519-sha256@libssh.org,ecdh-sha2-nistp256"
Local $sAllowed_hostKey = "ssh-ed25519,ecdsa-sha2-nistp256"
Local $sAllowed_cipher = "chacha20-poly1305@openssh.com,aes256-ctr"
Local $sAllowed_mac = "hmac-sha2-256,hmac-sha2-512"

$oJson.UpdateString("kex",$sAllowed_kex)
$oJson.UpdateString("hostKey",$sAllowed_hostKey)
$oJson.UpdateString("cipher",$sAllowed_cipher)
$oJson.UpdateString("mac",$sAllowed_mac)

;  Apply the allow-list.  This must be done before connecting.
$bSuccess = $oSsh.SetAllowedAlgorithms($oJson)
If ($bSuccess = False) Then
    ConsoleWrite($oSsh.LastErrorText & @CRLF)
    Exit
EndIf

Local $iPort = 22
$bSuccess = $oSsh.Connect("ssh.example.com",$iPort)
If ($bSuccess = False) Then
    ConsoleWrite($oSsh.LastErrorText & @CRLF)
    Exit
EndIf

ConsoleWrite("Connected." & @CRLF)

$oSsh.Disconnect