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Re: Yubiserver package ships with pre-filled identities
From: Jonathan Wiltshire <jmw () debian org>
Date: Mon, 30 Jan 2012 11:56:22 +0000

On 2012-01-30 06:43, Nanakos Chrysostomos wrote:
Hi again,
I found another reason for not shipping the package with an example
account. I think you are certainly right. If you haven't filled a bug
please do so, in the meanwhile I will upload to mentors a new version
with an empty database that resolves the problem. Thanks.

This populated database is also shipped in the upstream tarball, oss-security should be consulted to see whether a CVE identifier should be issued.

Adding to CC; oss-sec please see below:


On 30 Ιαν 2012, at 1:25, Gian Piero Carrubba <gpiero () rm-rf it> wrote:

Hi Nanakos,

thanks for your prompt response.

* [Sun, Jan 29, 2012 at 11:19:37PM +0200] Nanakos Chrysostomos:
those keys are invalid and are not my real keys. It's just a sample for the potential users of the package to see.

Ok, good for you :) .

According to yubico one in a billion or trillion I think , two users might have/use the same credentials aka public id, private id and aes key. I think there is no need to worry, but I might also be wrong.

While I certainly can be wrong, and surely I'm not a security expert, I strongly disagree about it not being a problem.

First of all consider that this is not the case of two users casually having the same credentials (anyway logging in two different services, think as the public id should be unique for every realm), but an authentication service that is preconfigured with known credentials.


Please refer to [0], §2.3.5:

Given the symmetric nature of the AES encryption algorithm, the security of the Yubikey relies that the AES key is logically and physically protected both in the key and in the server that verifies the OTP.

And in §6.1:

The Yubikey OTP generation is made up of the following fields

[..] Private (secret) id
[..] Usage counter
[..] Timestamp
[..] Session usage counter
[..] Random number
[..] CRC16 checksum

Where it is clear that the only authentication related field (apart from the aes key encrypting the string) is the private id.

This is also reflected in your validate_otp() implementation, where - given the decrypted otp - the only authentication check is against the private_id. The other checks that could lead to a BAD_OTP error (namely against crc and counter) are there only for invalidating data corruption and replay attacks.

Please at last note that the uid and the aes key cannot be retrieved from a yubikey. This is a security feature in order to protect the stored accounts, but as for the symmetric nature of the key it should be applied on both sides (yubikey and validation server).


Ciao,
Gian Piero.


[0] http://static.yubico.com/var/uploads/pdfs/YubiKey_Manual_2010-09-16.pdf

--
Jonathan Wiltshire                                      jmw () debian org
Debian Developer                         http://people.debian.org/~jmw

4096R: 0xD3524C51 / 0A55 B7C5 1223 3942 86EC  74C3 5394 479D D352 4C51


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