Tcl

SSH HSM Public Key Authentication

Demonstrates SSH public-key authentication using a private key stored on an HSM — a USB token or smart card — accessed through PKCS#11. A session is opened with the vendor's driver, the key handles are located, and an SshKey object is bound to them with UsePkcs11.

Background: The point of an HSM is that the private key is generated on the device and cannot be exported: the signing operation happens on the hardware, so the key material never reaches your application's memory or disk. Even a fully compromised host cannot yield a copy of the key. PKCS#11 is the vendor-neutral interface to such devices, which is why the driver path and the object-finding template are the only vendor-specific parts of this example.

Chilkat Tcl Downloads

Download Chilkat for Tcl

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 public-key authentication using a private key stored on an HSM (a USB token
#  or smart card) accessed through PKCS#11.
#  
#  Note: Chilkat's PKCS#11 implementation runs on Windows, Linux, macOS, and other supported
#  operating systems.

set pkcs11 [new_CkPkcs11]

#  The PKCS#11 driver supplied by your HSM vendor: a .dll on Windows, a .so on Linux, or a
#  .dylib on macOS.
CkPkcs11_put_SharedLibPath $pkcs11 "C:/Program Files (x86)/Gemalto/IDGo 800 PKCS#11/IDPrimePKCS1164.dll"

#  The PIN should come from a secure source rather than being hard-coded.
set pin "0000"

#  Normal user = 1
set userType 1

set success [CkPkcs11_QuickSession $pkcs11 $userType $pin]
if {$success == 0} then {
    puts [CkPkcs11_lastErrorText $pkcs11]
    delete_CkPkcs11 $pkcs11
    exit
}

#  Describe the private key object to be located on the HSM.
set json [new_CkJsonObject]

CkJsonObject_UpdateString $json "class" "private_key"
CkJsonObject_UpdateString $json "label" "MySshKey"

set priv_handle [CkPkcs11_FindObject $pkcs11 $json]
if {$priv_handle == 0} then {
    puts [CkPkcs11_lastErrorText $pkcs11]
    delete_CkPkcs11 $pkcs11
    delete_CkJsonObject $json
    exit
}

#  Find the corresponding public key by changing the class in the same template.
CkJsonObject_UpdateString $json "class" "public_key"

set pub_handle [CkPkcs11_FindObject $pkcs11 $json]
if {$pub_handle == 0} then {
    puts [CkPkcs11_lastErrorText $pkcs11]
    delete_CkPkcs11 $pkcs11
    delete_CkJsonObject $json
    exit
}

#  Create an SSH key object that uses the HSM handles.  The key type may be "rsa" or "ec".
set key [new_CkSshKey]

set keyType "rsa"
set success [CkSshKey_UsePkcs11 $key $pkcs11 $priv_handle $pub_handle $keyType]
if {$success == 0} then {
    puts [CkSshKey_lastErrorText $key]
    delete_CkPkcs11 $pkcs11
    delete_CkJsonObject $json
    delete_CkSshKey $key
    exit
}

set ssh [new_CkSsh]

set port 22
set success [CkSsh_Connect $ssh "ssh.example.com" $port]
if {$success == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkPkcs11 $pkcs11
    delete_CkJsonObject $json
    delete_CkSshKey $key
    delete_CkSsh $ssh
    exit
}

#  The corresponding public key must already be installed on the SSH server for the account.
#  The signing operation happens on the HSM -- the private key never leaves the device.
set success [CkSsh_AuthenticatePk $ssh "mySshLogin" $key]
if {$success == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkPkcs11 $pkcs11
    delete_CkJsonObject $json
    delete_CkSshKey $key
    delete_CkSsh $ssh
    exit
}

puts "Public-key authentication successful."

CkSsh_Disconnect $ssh

CkPkcs11_Logout $pkcs11
CkPkcs11_CloseSession $pkcs11

delete_CkPkcs11 $pkcs11
delete_CkJsonObject $json
delete_CkSshKey $key
delete_CkSsh $ssh