VB.NET
VB.NET
SSH Set Allowed Algorithms
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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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Dim success As Boolean = 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.
' -------------------------------------------------------------------------------------------
Dim ssh As New Chilkat.Ssh
Dim json As New 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.
Dim allowed_kex As String = "curve25519-sha256@libssh.org,ecdh-sha2-nistp256"
Dim allowed_hostKey As String = "ssh-ed25519,ecdsa-sha2-nistp256"
Dim allowed_cipher As String = "chacha20-poly1305@openssh.com,aes256-ctr"
Dim allowed_mac As String = "hmac-sha2-256,hmac-sha2-512"
json.UpdateString("kex",allowed_kex)
json.UpdateString("hostKey",allowed_hostKey)
json.UpdateString("cipher",allowed_cipher)
json.UpdateString("mac",allowed_mac)
' Apply the allow-list. This must be done before connecting.
success = ssh.SetAllowedAlgorithms(json)
If (success = False) Then
Debug.WriteLine(ssh.LastErrorText)
Exit Sub
End If
Dim port As Integer = 22
success = ssh.Connect("ssh.example.com",port)
If (success = False) Then
Debug.WriteLine(ssh.LastErrorText)
Exit Sub
End If
Debug.WriteLine("Connected.")
ssh.Disconnect()