Re: random, digest, uuid, cipher & Co

[David Haley <dchaley@...>]

PA wrote:

> I would like to simulate a public key infrastructure on the cheap for 
> authentication purpose... for example, two applications communicate 
> over SMTP and the server would like to authenticate the client...
>
> [snip]
>
> To validate a signature, the server call back the client with both the 
> original banner value as well as the signature it has received. The 
> client can then validate the signature by encrypting the value with 
> its private key and see if it matches.

If the client is in charge of validating the signature, where is your 
authentication? Are you worried about connection interception? Your 
protocol seems like it is very vulnerable to an intruder listening on 
the network who could impose as either one of the players.

As the others have pointed out, there is more to a secure protocol than 
throwing together lots of hashes and encryptions. You took out the 
shared secret; do you know what role it plays? Why is it important? Does 
your protocol allow client authentication to the server? What about 
server authentication to the client? Do you care about either/both of 
these? Cryptography is only a portion of the problems when it comes to 
protocols. Even a protocol that uses (theoretically!) unbreakable 
cryptography can be very vulnerable to imposture or authentication failure.

--
~David-Haley
http://david.the-haleys.org

p.s. Hi everybody! :-) I've been lurking for a while. The comments on
this list have been very useful in furthering my understanding of how
things should be done in Lua (i.e. the "Lua Way".) Thank you to all and
especially to the developers of this very fine language.