From: Hal <74076.1041@CompuServe.COM>
Date: Sat, 24 Oct 92 09:02:41 PDT
To: <cypherpunks@toad.com>
Subject: Multiple messages + entropy
Message-ID: <921024155350_74076.1041_DHJ67-1@CompuServe.COM>
MIME-Version: 1.0
Content-Type: text/plain


The Internet PEM (Privacy Enhanced Mail) standard uses the
concept which Dean Tribble mentioned of multiple encryption
(using each recipient's public key) of a single session key
which encrypts the message.  PGP's data structures do not
currently provide for this but could be extended pretty easily
to allow it.

On the entropy measure - I thought entropy was how many bits
of information you get per character.  Encrypted binary text
would be pretty close to 8 bits per character.  The RFC1113
Ascii encoding used by PGP reduces this to 6 bits per character
(e.g. a character set with 64 printable characters) neglecting
line separators and message beginnings and endings.  So there
should be a little less than 6 bits per character for encrypted,
Ascii-encoded messages.

Hal
74076.1041@compuserve.com