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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
References: