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Printable Version: RFC1244.PDF
RFC 1244 Site Security Handbook July 1991
3.9.2.2 Privacy Enhanced Mail
Electronic mail normally transits the network in the clear
(i.e., anyone can read it). This is obviously not the optimal
solution. Privacy enhanced mail provides a means to
automatically encrypt electronic mail messages so that a person
eavesdropping at a mail distribution node is not (easily)
capable of reading them. Several privacy enhanced mail
packages are currently being developed and deployed on the
Internet.
The Internet Activities Board Privacy Task Force has defined a
draft standard, elective protocol for use in implementing
privacy enhanced mail. This protocol is defined in RFCs 1113,
1114, and 1115 [7,8,9]. Please refer to the current edition of
the "IAB Official Protocol Standards" (currently, RFC 1200
[21]) for the standardization state and status of these
protocols.
3.9.3 Origin Authentication
We mostly take it on faith that the header of an electronic mail
message truly indicates the originator of a message. However, it
iseasy to "spoof", or forge the source of a mail message. Origin
authentication provides a means to be certain of the originator of
a message or other object in the same way that a Notary Public
assures a signature on a legal document. This is done by means of
a "Public Key" cryptosystem.
A public key cryptosystem differs from a private key cryptosystem
in several ways. First, a public key system uses two keys, a
Public Key that anyone can use (hence the name) and a Private Key
that only the originator of a message uses. The originator uses
the private key to encrypt the message (as in DES). The receiver,
who has obtained the public key for the originator, may then
decrypt the message.
In this scheme, the public key is used to authenticate the
originator's use of his or her private key, and hence the identity
of the originator is more rigorously proven. The most widely
known implementation of a public key cryptosystem is the RSA
system [26]. The Internet standard for privacy enhanced mail
makes use of the RSA system.
3.9.4 Information Integrity
Information integrity refers to the state of information such that
it is complete, correct, and unchanged from the last time in which
Site Security Policy Handbook Working Group [Page 37]