I question whether hiding the public key really is a valid method for
increasing security, even though it seems it should be at first sight.
If you want to access my private mail, which is sent to me with a
public-key cryptography scheme, you will have to find out my pair-key.
Which of this options would you prefer:
1. Having my mail & my public key.
2. Having my mail.
B. If you are going to share the public key with multiple users, how
private do you realistically expect the public key to remain?
C. If you are going to keep the public key private to prevent someone
(or some nasty government spy agency) from seeing the modulus and
factoring it, is this realistic? Can you really keep it private
Imagine that there are international enterprises using INTERNET.
Imagine (in the long future??) that they like it so much that decide to
use INTERNET to exchange information between the various delegations
around the world, instead of using private communication lines. Imagine
they believe the best solution to communicate between delegations is
MIME (because of time differences, implementation's cost of another
solution or even the great value of MIME).
In this case, it's not hard to to believe that the main delegation will
create a pair key, to use in communications who need top security. The
public key would be delivered in "hand" to the delegations. It's fair
to believe that the public key will only be available to people the
enterprise trusts (probably, those who have access to top security information).
factoring it, is this realistic? Can you really keep it private
forever if you are giving it out, albeit limitedly? In any case, this
criteria is not a stated goal of this standard.
It may not be a "stated goal of this standard", but that isnt a reason
to stop discussing it. Any way, the solution to this problem (if it is
a problem, as i think it is) is quite simple.
A. Are you going to share this "private" public key with only one
other user? If so, then why bother with public key cryptography? Why
not use DES instead?
Because if you find out the DES password, then all communications will
lost there confidentiality. With public key cryptography, if you find
out the public key (which is the chain more bounded to be broken in the
security scheme i described above) that doesn't unveil your information.
*NOTE* There is no perfect security scheme. I believe that scheme's
security increases as the complexity & work to break it grows.
I hope we have more time to discuss his issue.
Vitor Fernandes