[Security] About the Firefox 3 Security Dialog & others

Eric Rescorla ekr at rtfm.com
Sat Aug 23 08:56:14 CDT 2008


On Sat, Aug 23, 2008 at 5:46 AM, Pedro Melo <melo at simplicidade.org> wrote:
> Hi,
>
> On Aug 23, 2008, at 1:18 PM, Jonathan Schleifer wrote:
>
>> Am 23.08.2008 um 11:04 schrieb Dirk Meyer:
>>
>>> SAS does not work for me when I use bots. It also reduces it to one
>>> way removing the option of X.509 certificates which is something I
>>> need.
>>
>> I never said SAS should be the only way, we need multiple ways. I suggest
>> those:
>>
>> * SAS with mnemonics
>> * Fingerprint verification
>> * CA, but no CA added in the client by default (so the user has to trust
>> the CA manually, for example useful in a company so you don't have to verify
>> every co-worker)
>
> Exactly. For bots, I personally would create my own CA and tell those pesky
> little devils just to trust certificates signed by that.
>
> Profit!.
>
>
>>>> Having a 32-bit SAS encoded with Mnemonics (like already suggested
>>>> here) really sounds like a great idea.
>>>
>>> Why not encode a key fingerprint with Mnemonics? Looks like the same
>>> to the user.
>>
>> Only taking 32 bit of the fingerprint and using Mnemonics is insecure as
>> this is easy to forge - we already discussed it here.
>>
>> BTW: It was argued a lot that ESessions misses a cryptanalysis, but if we
>> are going to do extensions to TLS, we might need a cryptanalysis for this
>> stuff too. TLS is useless if we add a verification method that is insecure.
>
> Well, SAS and SRP are IETF (draft?) extensions. SRP has more than 10 years
> of field tests and debate (up to current SRP-6, I believe).

SRP isn't a draft. It's an RFC.

I agree we would need to do an SAS extension to TLS if we wanted SAS
and yes, that would need analysis. However, it's a relatively small
piece of work compared to a whole new protocol.

-Ekr


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