Thales Key Exchange Examples and Troubleshooting

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Judging from the searches done to locate this blog, it’s clear many of us share the following opinion: although Thales (formerly RACAL) is a market leader with its 7000 and 8000 series of HSM devices, their documentation falls painfully short in two areas: there are NO COMMAND EXAMPLES (!!!) in the manuals (an appalling omission); and the troubleshooting assistance is also distressingly thin. As a result, we had to lean heavily on our local Thales distributor for guidance on how commands really get pieced together. And, man, is it ever esoteric….see my earlier posts regarding the ‘KSN Descriptor’ for evidence of that. Moreover, our distributor provided us with some outstanding troubleshooting support to get us through the all important FA/FB key exhange. So, I’ll post our experience here in hopes that others can benefit from it.

The FA/FB is the command exchange to “Translate a ZPK from ZMK to LMK Encryption.” We had this working internally with some simulated stuff, but once we tried this command ‘for real’ with our Debit/EBT gateway partner , we consistently received parity errors back from our Thales 8000 HSM (i.e., the FB returned with some result code != 0).

There are three possible issues / resolution paths to explore in these situations:

Your switching partner has employed an Atalla HSM and you’ve not taken it into account. When a Thales/RACAL HSM ‘talks’ to an Atalla, your box commands must specify an Atalla Variant.

Your switching partner didn’t specify a Key Scheme in its ZPK creation, and the default is X9.17 (‘X’). If you specify the RACAL Scheme (‘U’) in your ‘FA’ and the ZPK under ZMK provided to the box was created via the X9.17 scheme, you’ll get a parity error.

You created the ZMK cryptogram internally using one key scheme and now are trying to employ it in the FA command specifying (inadvertantly) the other variant scheme.

You want to try to resolve each of these in turn.

The “test solution” path for Item #1 is as follows…

Let’s assume your FA command is constructed like so:

FAU2D775BFD****************FABE0D7CU6C0FDE16D22FF2D95273E3741AF4E187

[NOTE: I’ve obscured the ZMK Cryptogram here for blogging purposes only. The actual value is a 32-position hexidecimal string.]

If you discover that the other side is using an Atalla, you need to specify an “Atalla Variant,” which you do by specifying a ‘1’ at the end of the ‘FA’ command string:

FAU2D775BFD****************FABE0D7CU6C0FDE16D22FF2D95273E3741AF4E1871

The “test solution” path for Item #2 is as follows…

We find some endpoint partners have no idea which Key Scheme (X9.17 or Racal Native) they employed to create their keys. So, you may have to experiment. This FA command string says that the ZMK and ZPK were created using the RACAL native scheme (‘U’):

FAU2D775BFD****************FABE0D7CU6C0FDE16D22FF2D95273E3741AF4E187

To specify that the ZPK was created using the X9.17 scheme, you’d do the following:

FAU2D775BFD****************FABE0D7CX6C0FDE16D22FF2D95273E3741AF4E187

The “test solution” path for Item #3 is as follows…

When you created your ZMK (probably during a key ceremony involving a reconstitution of key parts provided by your endpoint gateway), you specify (or otherwise let default) your ZMK Key Scheme. Again, this can be either the RACAL Native Scheme (‘U’) or X9.17 (‘X’). [I believe the default is X9.17.] For example, if you created the ZMK using the ‘X’ approach, and then submitted an ‘FA’ command that looks like this:

FAU2D775BFD****************FABE0D7CU6C0FDE16D22FF2D95273E3741AF4E187

…it’s gonna fail. You absolutely must maintain consistency from the creation of the ZMK cryptogram through its subsequent usage. So, the command would change to look like this:

FAX2D775BFD****************FABE0D7CU6C0FDE16D22FF2D95273E3741AF4E187

[NOTE: I’m not advocating ‘X’ over ‘U’ here…just showing you an example. In a recent concluded project, we assumed the incoming ZPK was of the RACAL native variety, but it arrived from the remote partner as created under the X9.17 scheme. Thing is, the gateway team had no idea they had done that and could not articulate the difference. So, be prepared to experiment with every permutation of what I’ve described herein before ‘unlocking’ the solution.]

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