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SFTP Set Allowed SSH Algorithms

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Demonstrates the Chilkat SFtp.SetAllowedAlgorithms method, which configures the exact set of SSH algorithms permitted for the connection. 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 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 server. Otherwise the safer default is to let the library's ordering evolve as guidance changes.

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Local $bSuccess = False

;  Demonstrates the SFtp.SetAllowedAlgorithms method, which configures the exact set of SSH
;  algorithms permitted for the connection.  The only argument is a JsonObject.  It must be
;  called before Connect.
;  
;  -------------------------------------------------------------------------------------------
;  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 can make 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.
;  -------------------------------------------------------------------------------------------

$oSftp = ObjCreate("Chilkat.SFtp")

$oJson = ObjCreate("Chilkat.JsonObject")

;  The 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 (encryption):
;    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 (hash):
;    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 key-exchange, host-key, cipher (encryption), and mac (hash) algorithms, 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 before connecting.
$bSuccess = $oSftp.SetAllowedAlgorithms($oJson)
If ($bSuccess = False) Then
    ConsoleWrite($oSftp.LastErrorText & @CRLF)
    Exit
EndIf

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

ConsoleWrite("Connected." & @CRLF)

$oSftp.Disconnect