Re: National Identity Card

From: Stephen Naicken <stephennaicken_at_gmail.com>
Date: Tue, 22 Sep 2015 16:43:07 +0100

Hello Ish,

Thank you for the highlighting the Minister's comments, it helps to
clarify things.

On 22 September 2015 at 07:50, Ish Sookun <ish.sookun_at_lsldigital.mu> wrote:

> The fingerprint reader in one of the interviews of the Minister of
> Technology, Communication & Innovation, is mentioned as being "standalone".
> Key on-demand cannot be used in this case.

One of the disadvantages of an offline reader is the assumption of
implicit trustworthiness. If a device is no longer considered
trustworthy, for example, it is stolen, then there is no means for its
permissions to be revoked and it can continue to decrypt card data.

Assuming that the intention has always been to use offline readers,
this raises an important question as to why fingerprint templates were
stored in a database. If the reader is offline then it cannot use the
database in the matching process. Typically such a system would
operate by either: submitting the fingerprint minutiae from a
fingerprint scan to the server that performs the matching; or the
relevant template being pulled by the reader so that match-on-reader
or match-on-card can be executed. Hopefully there will be some
clarification on this.

>
> The use of a Security Access Module was mentioned by the Heads of Operations
> of the Mauritius National Identity Card project. It was said that the SAM
> contains the key to decrypt data stored in the ID Card. I would eliminate
> the use of unique keys. If the card reader is standalone and that the
> project used "unique keys", then a mechanism to update the reader with new
> keys (for freshly issued ID Cards) would be needed. There is no mention of
> such mechanism.

Having one decryption key is a weakness, so I would hope (and expect)
that the system operates using a form of key derivation [1] to derive
a unique key for each card. Each and every SAM would contain the same
master key. At a high-level, this could work as follows: the smart
card presents its identity to the reader, this could be a public-key
or the NIC number or some combination of unique identity data; the
SAM implements a function, such as a cryptographic hash function [2]
using the master key and the smart card identity; the result of the
function is a key unique to that card to decrypt its data. This
eliminates the need to update the reader.

This approach increases the complexity of an attack. Knowing a given
smart card's key will compromise neither the master key, nor any other
smart card. Additionally, if the master key is leaked, as long as the
key derivation algorithm is unknown, an attacker can not derive the
key for a given individual's identity card.

[1] https://en.wikipedia.org/wiki/Key_derivation_function
[2] https://en.wikipedia.org/wiki/Cryptographic_hash_function
Received on Tue Sep 22 2015 - 15:44:04 PST

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