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RE: Rest of World encryption hardware products?



>>>>> "NMP" == NMP  <Lehtonen> writes:

 NMP> Paul Koning writes:
 >> A Vernam cypher has a random key of length equal to the plaintext.
 >> Period.  Full stop.  Then and only then will it have the "provably
 >> unbreakable" property that makes it unique among cryptosystems.

 NMP> Handbook of Applied Cryptography by Menezes, van Oorschot and
 NMP> Vanstone defines Vernam cipher as follows:

 NMP> The Vernam Cipher is a stream cipher defined on the alphabet A =
 NMP> {0, 1}. A binary message m1 m2 ... mt is operated on by a binary
 NMP> key string k1 k2 ... kt of the same length to produce a
 NMP> ciphertext string c1 c2 ... ct where ci = mi XOR ki, 1 <= i <=
 NMP> t.  If the key string is randomly chosen and never used again,
 NMP> the Vernam cipher is called a one-time system or a one-time pad.

 NMP> The definition of stream cipher does not require that the
 NMP> keystream be random.

Hm, that's very interesting.

Up to now I've only seen the term "Vernam cypher" used as a synonym of
"One time pad".  (If my memory of Kahn's book serves, Vernam himself
was using it that way.)  I was using it in that sense, and the snake
oil I was commenting on was doing likewise.  Of course it's only the
one time pad (random stream, not reused) that has the provably secure
property.

	paul


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