dovecot - May 2004 - using one-time passwords

Hi,

Is there any way to use something like OPIE (one-time passwords in
everything, S/KEY) with dovecot?

Here's what I want to do ultimately:
 * have an AUTH=XYZ method that relies on S/KEY as provided by the
   libpam-opie module (well, maybe not through pam)
 * have dovecot advertise authentication as follows:
   - local               : PLAIN, XYZ
   - remote (encrypted)  : EXTERNAL, and rely on certificate
   - remote (unencrypted): XYZ

Thats the dovecot part. Then I would modify squirrelmail to
  a) negotiate PLAIN with an authorized web client certificate
  b) negotiate XYZ when without SSL or SSL without a valid certificate

This way I could check my mail even from computers that I don't trust at
all to not do key-logging, since I can have an S/KEY generator on my
cell-phone.

Does this sound feasible? I see the following advantages:
 * allows checking of webmail on the road, on untrusted computers, 
   giving out only whatever you decide to look at
 * allows checking of mail via unencrypted IMAP, relying on one-time
   passwords so giving an attacker only whatever he can look at while
   your session is active (assuming he can't insert anything into the
   tcp stream...)
 * is otherwise encrypted, and then doesn't force using one-time keys
   which may be somewhat a hassle to generate.

johannes
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 832 bytes
Desc: This is a digitally signed message part
URL:
<http://dovecot.org/pipermail/dovecot/attachments/20040513/f7477224/attachment-0001.bin>

On Thu, 2004-05-13 at 20:16, Johannes Berg wrote:
> Hi,
> 
> Is there any way to use something like OPIE (one-time passwords in
> everything, S/KEY) with dovecot?
> 
> Here's what I want to do ultimately:
>  * have an AUTH=XYZ method that relies on S/KEY as provided by the
>    libpam-opie module (well, maybe not through pam)
I didn't really understand how libpam-opie works. Does it require some
special client or how does it tell the seed/sequence? Or doesn't it?

But sure, Cyrus SASL has AUTH=OTP mechanism, we could be compatible with
that. Want to write it? :) Shouldn't be hard to plug into Dovecot, I
just don't really have time right now.

The OTP-data could be stored in same way as
PASSDB_CREDENTIALS_DIGEST_MD5. Except the code doesn't currently allow
multiple credentials per user, it only uses the beginning of the
password field to specify the password type, eg. "{PLAIN}password",
"{DIGEST-MD5}digest-md5-credentials", etc. I guess I should do
something
about that..
>  * have dovecot advertise authentication as follows:
>    - local               : PLAIN, XYZ
>    - remote (encrypted)  : EXTERNAL, and rely on certificate
>    - remote (unencrypted): XYZ
> 
> Thats the dovecot part. Then I would modify squirrelmail to
>   a) negotiate PLAIN with an authorized web client certificate
>   b) negotiate XYZ when without SSL or SSL without a valid certificate
1.0-test9 supports "ssl_verify_client_cert" option, but then it always
requires it .. hmm. maybe with it enabled the configuration could
support something like:

auth default {
  mechanisms = plain
  ..
  ssl_require_client_cert = yes
}

auth otp {
  mechanisms = otp
  ..
  ssl_require_client_cert = no
}

Yes, that looks good, I'll implement that.
> Does this sound feasible? I see the following advantages:
>  * allows checking of webmail on the road, on untrusted computers, 
>    giving out only whatever you decide to look at
One problem is that it also gives the possibility to modify the mailbox
which isn't very good. From my TODO:

 - support read-only logins. user could with alternative password get only
   read-access to mails so mails could be read relatively safely with
   untrusted computers. Maybe always send [ALERT] about the previous
   read-only login time with IP?

Maybe flag changes would be allowed (but not \Deleted). Anyway, this
could be configurable as well (append :READONLY to default_mail_env).

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 189 bytes
Desc: This is a digitally signed message part
URL:
<http://dovecot.org/pipermail/dovecot/attachments/20040517/2477e47f/attachment-0001.bin>

On Mon, May 17, 2004 at 03:24:51AM +0300, Timo Sirainen
wrote:
> The OTP-data could be stored in same way as
> PASSDB_CREDENTIALS_DIGEST_MD5. Except the code doesn't currently allow
> multiple credentials per user, it only uses the beginning of the
> password field to specify the password type, eg.
"{PLAIN}password",
> "{DIGEST-MD5}digest-md5-credentials", etc. I guess I should do
something
> about that..
Please keep it as compatible as possible with the equivalent LDAP
scheme!  (Also bearing in mind that LDAP permits multiple credentials
per user, although it can't do anything much sophisticated than
retrieving them).

Thanks
Joshua.

-- 
Joshua Goodall                           "as modern as tomorrow
afternoon"
joshua at roughtrade.net                                       - FW109