For those who are concerned about key spoofing, it makes sense to specify
how authentication will work. But to make authentication mandatory, while
confidentiality is only optional, simply doesn't meet our goals.
Doug
Doug,
After reading your 20+ mail messages over the last week I am still
unable to understand your concerns. It seems to be that the PEM
RFCs have the word "privacy" in the their title, but that privacy is
an optional feature of the services supplied. But this makes sense.
If we know each other and have agreed upon a key through some out-of-band
mechanism, then we can obtain privacy by using that key to encrypt our
messages to one another. We do not need PEM or any other extensions to
the mail protocols to do so, and we do not need any key management
infrastructure to support us. We need only encrypt our messages using
"crypt", DES or whatever we have agreed upon and then uuencode them -
just as everyone has been doing all these years. From your messages,
this seems to be what you want, so why even use PEM? You just need a
modified user agent to keep track of the various keys you are using
for your correspondence.
But if we wish to obtain the advantages of cryptographic technologies for
larger scale activities, such as EDI and the like, we are forced into
accepting some form of on-line key management, for it is not possible to
pre-establish shared keys with everyone with whom we might have business
dealings before we have a need to interact with them. And as we might
not know them personally, we also require some mechanism for establishing
a level of trust in our dealings with them, the focus of another recent
discussion on this mailing list.
This is the primary reason for the existence of PEM. Without the key
management there is no need to modify the mail protocols. With key
management you do, and you wind up with a PEM, X.411, PGP, MSP, MOSAIC,
or something similar. All of these protocols require authentication and
make privacy optional. Some also make integrity optional. Why? Because
all of their developers have concluded that exchanging keys on-line doesn't
do you any good unless you are sure of whom you have exchanged keys with.
You must have authentication built into key management. You can only
achieve integrity, privacy or non-repudiation after authentication. As
it seemed onerous to require all services for every message, the other
services were made optional.
Charlie Watt
SecureWare, Inc.