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Subject: Re: Security Working Group meeting - Wednesday August 4 - ibm-acf repo
To: Patrick Williams <patrick@stwcx.xyz>
References: <89b3524f-a1b3-513c-fc6a-1d888e479238@linux.ibm.com>
 <YQoIBwTVJZcqTEMU@heinlein>
From: Joseph Reynolds <jrey@linux.ibm.com>
Message-ID: <9c7dc355-1926-babc-d329-efdb7ece1a20@linux.ibm.com>
Date: Mon, 9 Aug 2021 09:09:04 -0500
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On 8/3/21 10:22 PM, Patrick Williams wrote:
> On Tue, Aug 03, 2021 at 05:57:52PM -0500, Joseph Reynolds wrote:
>> This is a reminder of the OpenBMC Security Working Group meeting
>> scheduled for this Wednesday August 4 at 10:00am PDT.
>>
>> We'll discuss the following items on the agenda
>> <https://docs.google.com/document/d/1b7x9BaxsfcukQDqbvZsU2ehMq4xoJRQvLxxsDUWmAOI/edit>,
>> and anything else that comes up:
>>
>>   1. (Joseph): IBM ACF design (2FA authentication for the special IBM
>>      service account) is in review -
>>      https://gerrit.openbmc-project.xyz/c/openbmc/docs/+/45201
>>      <https://gerrit.openbmc-project.xyz/c/openbmc/docs/+/45201>
> I still feel like the "Alternatives considered" are pretty weak in this
> document.  Rather than paint broad brushes ("Other were considered.  They were
> not suitable.") I think you should enumerate _which_ alternatives were
> considered and _why_ they don't fit the problem at hand.

You're right, I rushed that section.  I will fill in some details. Thanks!

> ```
> - Takes four parameters: machine serial number, expiration date, password, and
>    private key.
> - Algorithm:
>     - Hashes the password.
>     - Creates the ACF from the hashed password, serial number, and expiration date.
>     - Digitally signs the ACF using the private key.
>     - Returns the ACF to the caller.
> ```
>
> This sounds a lot like U2F.  The "4 parameters" are the challenge, IBM's key
> signing server is the U2F device, and PAM is the "Relying Party".  There are
> already PAM modules for some aspects of U2F and the token you need to exchange
> is reasonably short (my Yubikey output is 33 characters).
>
> https://developers.yubico.com/U2F/Protocol_details/Overview.html
>
> The nice aspect if you can reuse portions of the U2F protocol is that you go a
> long way towards enabling others to add more typical 2FA like Yubikeys.

We discussed this an email exchange ending 2021 March 9 "Request new 
repo for IBM-specific code - pam_2fa discussion".  Although I could use 
the U2F module, it is not a good fit because the ACF credential flow 
does not fit well under the U2F protocol.  I'll excerpt that 
conversation and add details to the design.

Joseph