[MlMt] Security

[Steven M. Bellovin]

On 17 Jan 2018, at 10:49, Bill Cole wrote:

> On 17 Jan 2018, at 8:06, Steven M. Bellovin wrote:
>
>> On 17 Jan 2018, at 5:51, Benny Kjær Nielsen wrote:
> [...]
>>> I back you up. Only thing to add is that one should make sure that 
>>> SSL is always enabled such that a password is never sent to the 
>>> IMAP/SMTP server in plain text. Note that most proper email servers 
>>> wouldn't even allow non-SSL connections.
>>>
>> What authentication options that don't involve sending passwords does 
>> MailMate support? Is there a way to configure MM to use only one of 
>> these safer options if available?
>
> I can't answer that, but I do take issue with the implied assertion 
> that it is inherently safer to use CRAM-MD5, DIGEST-MD5, or other 
> password-based mechanisms that avoid send the password to the server 
> in decodable form rather than using a plaintext mechanism via an 
> encrypted (i.e. TLS) transport. To support those mechanisms, the 
> server needs to *store* a recoverable form of the password, which in 
> most circumstances creates a less protectable attack surface than 
> putting a password on the wire inside an encrypted channel to a server 
> that only stores strong one-way hashes.
>
It varies, depending on the design. Client-side certificates require 
only a public key on the far end. Both sides could store hashed 
passwords (see https://tools.ietf.org/html/draft-bellovin-hpw-01 -- 
alas, it went nowhere) for one design.

But there's a more subtle issue: when you make your trust decisions.  
*If* you trust the site to store passwords safely -- and I agree; that's 
a big assumption -- you make the trust decision once. When you send 
passwords in the clear, you're making that trust decision every time you 
log in, and you're trusting the certificate issuance (think Diginotar 
and Comodo), corporate firewalls that terminate every TLS session and 
create a new one, users who click "OK" to certificate warnings, and 
more.


         --Steve Bellovin, https://www.cs.columbia.edu/~smb