Re: storing HA1 password hash for HTTP DIGEST, SIP, TURN

[Daniel Pocock <daniel@pocock.pro>]

(re-sent due to mailing list issue)

On 16/07/15 13:09, Howard Chu wrote:
> Daniel Pocock wrote:
>>
>>
>> On 13/07/15 11:37, Daniel Pocock wrote:
>>>
>>>
>>> On 13/07/15 11:03, Michael Ströder wrote:
>>>> Daniel Pocock wrote:
>>>>> There are a few protocols that use a HA1[1] password hash, such as
>>>>> HTTP
>>>>> DIGEST[1], SIP DIGEST[2] and TURN[3] (which uses HMAC rather than
>>>>> DIGEST)
>>>>>
>>>>> Is there a standard LDAP attribute name for storing a HA1 value or
>>>>> should it be stored in a regular userPassword attribute as
>>>>> described in
>>>>> the manual[4]?
>>>>
>>>> Do you want to use the LDAP server only as dumb password store or do
>>>> you also
>>>> want to use this attribute for LDAP bind operation?
>>>>
>>>
>>> Good question
>>>
>>> For the DIGEST and HMAC algorithms, the most interesting possibility
>>> would be for OpenLDAP to perform validation:
>>>
>>> 1. HTTP server (or SIP proxy or whatever) creates a challenge header and
>>> sends it to the end user
>>> 2. User responds with an authorization token
>>> 3. HTTP server gives a copy of the challenge and the response to the
>>> OpenLDAP server
>>> 4. OpenLDAP gives a validation true/false response
>>>
>>> In this case, clients can't read the HA1 from LDAP
>>>
>>> Could that be done with a bind?  Does it have any performance impact
>>> doing a bind or is there a more lightweight way to achieve this?
> 
> You can't pass all the necessary parameters (nonce, challenge, uri,
> etc.) to the LDAP server using a Simple Bind request. But e.g. HTTP
> DIGEST is the same as the SASL DIGEST-MD5 mechanism. You could pass thru
> the parameters from an LDAP SASL Bind request, with the HTTP (or
> whatever) server just acting as a MITM. Note that in that case, the LDAP
> server's SASL library generates the challenge, the HTTP server must
> parse it and pass it on to the client.
> 
> There's no particular performance impact for Bind itself; whatever
> crypto the underlying mechanism uses will have its own cost of course.
> 
>>> There is already a similar solution for RADIUS, rlm_digest
>>> http://freeradius.org/radiusd/man/rlm_digest.txt
> 
>> I'm just wondering if anybody can give any more feedback about this
>> issue before I look at coding anything for it?
>>
>>
>>
> 
> 

Thanks for the feedback on this issue.

What you describe using SASL may work for HTTP and SIP because they both
use DIGEST.  SIP DIGEST is very similar to HTTP DIGEST.

TURN (RFC 5766), however, uses HMAC.  It still uses the same HA1 hashed
version of the secret as an input to the algorithm.

If the OpenLDAP server stores plaintext passwords, the HA1 value can be
created on the fly for DIGEST or HMAC challenge/response.

If the OpenLDAP server doesn't store plaintext passwords, then the HA1
values need to be stored in attributes and those attributes need to be
updated whenever the user does a password change.

Regards,

Daniel