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The following archive was created by hippie-mail 7.98617-22 on Fri Aug 21 1998 - 17:16:20 ADT
KDBriggs1 (KDBriggs1@aol.com)
Fri, 27 Mar 1998 13:05:04 EST
I just read Ron Rivest's Chaffing and Winnowing paper. If his technique is
not classified as encryption then it seems I could make a logical extension
using the technique described below and it wouldn't be classified as
encryption either. I somehow doubt the U.S. gov't would agree, however.
Alice and Bob share a secret key. Alice salts her key with a random number
and runs the result through an RC4 key schedule. She then cycles the RC4
stream generator and obtains a bit stream equal in length to her plaintext.
The salt is sent to Bob in the clear. Whenever there is a 0 in the RC4
stream, she sends Bob the corresponding plaintext bit followed immediately by
the complement of that bit. Whenever there is a 1 in the RC4 stream, she
first sends the complement of the corresponding plaintext bit followed
immediately by the actual plaintext bit. Using Rivest's terms, Bob will
receive a message of 50% chaff and 50% wheat (plus a salt value).
Bob appends the salt to the secret key and runs the RC4 key schedule and
begins producing the key stream. He pulls the bits off in pairs from the
received message. When the RC4 stream produces a 0, he keeps the first bit
and discards the second, and when it produces a 1, he discards the first bit
and keeps the second, thus reconstructing the original message.
Message: 1 0 0 1 1 0 1 0
RC4 stream: 0 0 1 0 1 0 1 1
chaff&wheat: 10 01 10 10 01 01 01 10
Technically, the entire message is sent in the clear. It's just not obvious
if the wheat bit is the first or the second bit in the bit pairs. Now what do
you think would happen if I applied for an export license for software using
this technique without putting a 40-bit restraint on the key size?
Kent Briggs
Briggs Softworks, www.briggsoft.com
The following archive was created by hippie-mail 7.98617-22 on Fri Aug 21 1998 - 17:16:20 ADT