Tcl

SSH Host Key Fingerprint

Demonstrates getting the SSH server's host key fingerprint after connecting. The HostKeyFingerprint property returns the classic MD5 form, while GetHostKeyFP returns a fingerprint using a chosen hash algorithm, with optional inclusion of the key type and hash name.

Background: The host key fingerprint identifies the server, and comparing it against a known-good value is how a client implements host-key pinning — detecting a man-in-the-middle or a server whose key has changed. This is the same fingerprint an SSH client shows on first connection when it asks whether to trust the host. Prefer SHA256, which is the modern standard; MD5 fingerprints still appear in older tooling but are cryptographically weak.

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Tcl


load ./chilkat.dll

set success 0

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

#  Demonstrates getting the SSH server's host key fingerprint after connecting.

set ssh [new_CkSsh]

set hostname "ssh.example.com"
set port 22
set success [CkSsh_Connect $ssh $hostname $port]
if {$success == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

#  The classic MD5 fingerprint is available as a property.
set md5_fingerprint [CkSsh_hostKeyFingerprint $ssh]
puts "$md5_fingerprint"
#  For example:  ssh-rsa 3072 21:b0:d8:41:4e:ef:78:10:20:af:01:b7:71:5d:eb:94

#  GetHostKeyFP returns a fingerprint using the hash algorithm of your choice, such as SHA256,
#  SHA384, or SHA512.  The 2nd and 3rd arguments control whether the key type and the hash name
#  are included in the returned string.
set includeKeyType 1
set includeHashName 1
set sha256_fingerprint [CkSsh_getHostKeyFP $ssh "SHA256" $includeKeyType $includeHashName]
if {[CkSsh_get_LastMethodSuccess $ssh] == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

puts "$sha256_fingerprint"
#  ssh-rsa SHA256:Ufgj480OsdsCZRjj9sSNM6fpgIcSJ61RsIG8usndUIY=

set includeKeyType 0
set includeHashName 1
set sha256_fingerprint [CkSsh_getHostKeyFP $ssh "SHA256" $includeKeyType $includeHashName]
if {[CkSsh_get_LastMethodSuccess $ssh] == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

puts "$sha256_fingerprint"
#  SHA256:Ufgj480OsdsCZRjj9sSNM6fpgIcSJ61RsIG8usndUIY=

set includeKeyType 1
set includeHashName 0
set sha256_fingerprint [CkSsh_getHostKeyFP $ssh "SHA256" $includeKeyType $includeHashName]
if {[CkSsh_get_LastMethodSuccess $ssh] == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

puts "$sha256_fingerprint"
#  ssh-rsa Ufgj480OsdsCZRjj9sSNM6fpgIcSJ61RsIG8usndUIY=

set includeKeyType 0
set includeHashName 0
set sha256_fingerprint [CkSsh_getHostKeyFP $ssh "SHA256" $includeKeyType $includeHashName]
if {[CkSsh_get_LastMethodSuccess $ssh] == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

puts "$sha256_fingerprint"
#  Ufgj480OsdsCZRjj9sSNM6fpgIcSJ61RsIG8usndUIY=

CkSsh_Disconnect $ssh

delete_CkSsh $ssh