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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: Magnus Hagander <magnus@hagander.net>
Cc: Stephen Frost <sfrost@snowman.net>
Cc: Álvaro Hernández Tortosa <aht@8kdata.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Some thoughts about SCRAM implementation
Date: Wed, 12 Apr 2017 12:09:04 -0400
Message-ID: <8328.1492013344@sss.pgh.pa.us> (raw)
In-Reply-To: <20a91441-fa4c-ec2c-d813-c549066b8055@iki.fi>
References: <df8c6e27-4d8e-5281-96e5-131a4e638fc8@8kdata.com>
	<a990783c-44b3-cff6-7128-c6393be41af6@iki.fi>
	<729b548a-f434-f31c-15e7-59f44aaecc8d@8kdata.com>
	<20170410183230.oxagjpfgj6xxmcwx@alap3.anarazel.de>
	<fd4530e0-f016-4eb9-a0d0-e32824482db5@8kdata.com>
	<20170412004118.GC20340@momjian.us>
	<20170412005830.GU9812@tamriel.snowman.net>
	<20170412012532.GF20340@momjian.us>
	<CABUevEwJO6QNmZVzARPf-nePv07ne1R=o73VQ2Oq6cn_+beJ_w@mail.gmail.com>
	<ee93b36d-59d2-35e6-dd0c-fb7c9cc65e0c@iki.fi>
	<20170412152629.GI20340@momjian.us>
	<20a91441-fa4c-ec2c-d813-c549066b8055@iki.fi>
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Heikki Linnakangas <hlinnaka@iki.fi> writes:
> On 04/12/2017 06:26 PM, Bruce Momjian wrote:
>> How does it do that?

> Good question, crypto magic? I don't know the details, but the basic 
> idea is that you extract a blob of data that uniquely identifies the TLS 
> connection. Using some OpenSSL functions, in this case. I think it's a 
> hash of some of the TLS handshake messages that were used when the TLS 
> connection was established (that's what "tls-unique" means). That data 
> is then incorporated in the hash calculations of the SCRAM 
> authentication. If the client and the server are not speaking over the 
> same TLS connection, they will use different values for the TLS data, 
> and the SCRAM computations will not match, and you get an authentication 
> failure.

... which the user can't tell apart from having fat-fingered the password,
I suppose?  Doesn't sound terribly friendly.  A report of a certificate
mismatch is far more likely to lead people to realize there's a MITM.

So this seems more like a hack than like a feature we need so desperately
as to push it into v10 post-freeze.

			regards, tom lane


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