Tcl

SSH Tunnel Authenticate with Secure Strings

Demonstrates SSH tunnel password authentication using SecureString objects, with the credentials read from an encrypted JSON config file and decrypted directly into secure strings rather than being hard-coded in source.

Background: The SshTunnel class runs the tunnel on a background thread, so it authenticates once and then serves connections until closed — which makes protecting the stored credential especially worthwhile. Decrypting straight into a SecureString avoids ever holding the password in an ordinary string, and the value stays encrypted in memory under a randomly generated session key. In production the decryption key itself would come from a key vault or OS keystore rather than a literal.

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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 SSH tunnel password authentication using SecureString objects, with the
#  credentials read from an encrypted config file rather than hard-coded in source.

#  Imagine the login and password were previously encrypted and saved in a JSON config file:
#  {
#    "ssh_login": "2+qylFfC56Ck7OQQt/U2/w==",
#    "ssh_password": "5neIq9Jmn0E3p71N6Yc8TA=="
#  }
set json [new_CkJsonObject]

set success [CkJsonObject_LoadFile $json "qa_data/passwords/ssh.json"]
if {$success == 0} then {
    puts [CkJsonObject_lastErrorText $json]
    delete_CkJsonObject $json
    exit
}

#  These are the encryption settings used when the credentials were encrypted.  In a real
#  application the key would come from a secure source, not a literal.
set crypt [new_CkCrypt2]

CkCrypt2_put_CryptAlgorithm $crypt "aes"
CkCrypt2_put_CipherMode $crypt "cbc"
CkCrypt2_put_KeyLength $crypt 128
CkCrypt2_SetEncodedKey $crypt "000102030405060708090A0B0C0D0E0F" "hex"
CkCrypt2_SetEncodedIV $crypt "000102030405060708090A0B0C0D0E0F" "hex"
CkCrypt2_put_EncodingMode $crypt "base64"

#  Decrypt directly into SecureString objects.  The values stay encrypted in memory, now under
#  a randomly generated session key.
set ssLogin [new_CkSecureString]

set ssPassword [new_CkSecureString]

CkCrypt2_DecryptSecureENC $crypt [CkJsonObject_stringOf $json "ssh_login"] $ssLogin
CkCrypt2_DecryptSecureENC $crypt [CkJsonObject_stringOf $json "ssh_password"] $ssPassword

set tunnel [new_CkSshTunnel]

set port 22
set success [CkSshTunnel_Connect $tunnel "ssh.example.com" $port]
if {$success == 0} then {
    puts [CkSshTunnel_lastErrorText $tunnel]
    delete_CkJsonObject $json
    delete_CkCrypt2 $crypt
    delete_CkSecureString $ssLogin
    delete_CkSecureString $ssPassword
    delete_CkSshTunnel $tunnel
    exit
}

#  Authenticate using the secure strings.
set success [CkSshTunnel_AuthenticateSecPw $tunnel $ssLogin $ssPassword]
if {$success == 0} then {
    puts [CkSshTunnel_lastErrorText $tunnel]
    delete_CkJsonObject $json
    delete_CkCrypt2 $crypt
    delete_CkSecureString $ssLogin
    delete_CkSecureString $ssPassword
    delete_CkSshTunnel $tunnel
    exit
}

puts "SSH tunnel authentication successful."

#  ... use the tunnel ...

set waitForThreadExit 1
set success [CkSshTunnel_CloseTunnel $tunnel $waitForThreadExit]
if {$success == 0} then {
    puts [CkSshTunnel_lastErrorText $tunnel]
    delete_CkJsonObject $json
    delete_CkCrypt2 $crypt
    delete_CkSecureString $ssLogin
    delete_CkSecureString $ssPassword
    delete_CkSshTunnel $tunnel
    exit
}


delete_CkJsonObject $json
delete_CkCrypt2 $crypt
delete_CkSecureString $ssLogin
delete_CkSecureString $ssPassword
delete_CkSshTunnel $tunnel