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Re: Writing svn-agent (Was Re: [PATCH] default to --no-auth-cache)

From: Benjamin Pflugmann <benjamin-svn-dev_at_pflugmann.de>
Date: 2003-01-16 07:57:38 CET

On Wed 2003-01-15 at 22:58:06 -0600, Karl Fogel wrote:
> Benjamin Pflugmann <benjamin-svn-dev@pflugmann.de> writes:
> > Although I am no security expert, I am a bit interested in that topic.
> > The claim you made (that a plain text password in a read-protected
> > file is equally secure as an encypted one which is only held in plain
> > in memory) sounds absurd to me. For a start, the exposure time is not
> > the same: The one is always available, even after you deleted it
> > (backups), while the other is only available while you are working
> > with it (the encrypted form is always avaiable, but let's hope that
> > the encryption is good and your passphrase, too).
>
> If the password is stored in memory *encrypted*, then yes, it is more
> secure.

No, I meant the way ssh-agent works: encrypted key on disk, plain text
key (or passphrase) in memory. Else, you would have to type your
passphrase each time it is accessed and nothing would be won (in terms
of usability).

If you don't want to use a key, but only password authentication, it
would store nothing on disk and simply cache your plain text password
in memory.

> But it is also less convenient, because now we've introduced one
> more passphrase into the user's experience -- so we're no longer
> comparing the same things.

It sounds as if you meant the simple password caching case
originally. It doesn't matter, my point was about the storing
mechanism: short time in-memory vs. long time on disk.

> If we don't introduce that extra passphrase, then the security is
> comparable between the two schemes, though the agent password is
> harder to get at, in terms of inconvenience for the attacker.

IMNSHO, it isn't. It is a difference by at least an order of
magnitude.

For a start, "harder to get at" is all what security is about. There
is no way to prevent 100% that someone gets at your data. You can only
make it as hard as possible (and reasonable). So you effectively just
said yourself that it is more secure.

Also, the window of exposure that I mentioned in my last mail, should
be enough to make it obvious. If it is cached in memory after I typed
it, an attacker has to target my session and his attack has to work
the first time or he may not get a second try (if I notice the attack
due to a crash or something). If it is saved on disk, he can attack
any time he likes, even if I am on vacation for a month.

    Benjamin.

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Received on Thu Jan 16 07:58:25 2003

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