Cryptography – Communication system using cryptography
Reexamination Certificate
2000-02-17
2001-07-24
Peeso, Thomas R. (Department: 2767)
Cryptography
Communication system using cryptography
C380S028000
Reexamination Certificate
active
06266417
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to cryptographic systems. In particular, the present invention relates to a system for encrypting plaintext messages and decrypting ciphertext communications.
BACKGROUND OF THE INVENTION
In the modern world, communications are passed between parties in a variety of different ways utilizing many different communications media. Electronic communication is becoming increasingly popular as an efficient manner of transferring information, and electronic mail in particular is proliferating due to the immediacy of the medium.
Unfortunately, drawbacks accompany the benefits provided by electronic communication, particularly in the area of privacy. Electronic communications may be intercepted by unintended recipients. Wireless transmissions, such as voice communication by cellular telephone, and electronic mail are especially susceptible to such interception.
The problem of electronic communication privacy has been addressed, and solutions to the problem have been put in place. One form of solution uses cryptography to provide privacy for electronic communication. Cryptography involves the encrypting or encoding of a transmitted or stored message, followed by the decryption or decoding of a received or retrieved message. The message usually takes the form of a digital signal, or a digitized analog signal. If the communication is intercepted during transmission or is extracted from storage by an unauthorized entity, the message is worthless to the interloper, who does not possess the means to decrypt the encrypted message.
In a system utilizing cryptography, the encrypting side of the communication incorporates an encoding device or encrypting engine. The encoding device accepts the plaintext (unencrypted) message and a cryptographic key, and encrypts the plaintext message with the key according to an encrypt relation that is predetermined for the plaintext communication and the key. That is, the message is manipulated with the key in a predetermined manner set forth by the text/key relation to produce a ciphertext (encrypted) message.
Likewise, the decrypting side of the communication incorporates a decoding device or decrypting engine. The decoding device accepts the ciphertext message and a cryptographic key, and decrypts the ciphertext message with the key according to a decrypt relation that is predetermined for the ciphertext message and the key. That is, the message is manipulated with the key in a predetermined manner set forth by the text/key relation to produce a new plaintext message that corresponds with the original plaintext message.
The manner in which the key and the relation are applied in the communication process, and the manner in which keys are managed, define a cryptographic scheme. There are many conventional cryptographic schemes in use today. For example, probably the most popular of these is a public-key cryptographic scheme. According to a scheme of this type, the keys used are actually combinations of a public key component that is available to anyone or to a large group of entities, and a private key component that is specific to the particular communication.
An important consideration in determining whether a particular cryptographic scheme is adequate for the application is the degree of difficulty necessary to defeat the cryptography, that is, the amount of effort required for an unauthorized person to decrypt the encrypted message. There are a number of ways an unauthorized person may go about attempting to defeat the cryptography of a system. Three of the most popular attacks on cryptographic systems are key exhaustion attacks (trial and error), differential cryptanalysis, and algebraic attacks. Choosing more complicated text/key relations and longer keys are two ways to make a cryptographic scheme less vulnerable to attack, but result in a more expensive system that operates at a slower speed. Thus, unless a clever cryptographic scheme is devised to avoid successful attack, tradeoffs must be made when deciding the level of privacy to be provided.
Once a scheme for effecting cryptography is chosen to suit the constraints of the particular application, the text/key relation is usually the determining factor in how successful the cryptography will be in defeating attacks. This in turn affects the confidence that the parties to a communication will have that their communication will remain private.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a process and apparatus for safeguarding the privacy of an electronic communication.
It is a further object of the present invention to provide a process and apparatus for encoding and decoding digital data.
One embodiment of the present invention includes a communication system, which includes an origination space, a communications channel, and a destination space associated with the origination space via the communications channel. The origination space includes an encryption engine for generating an output symbol O
t
based on an input symbol I
t
and means for receiving an encrypt key, an encrypt text/key relation, and the input symbol. The destination space includes a decryption engine for generating a decrypted symbol I′
t
based on the output symbol received from the origination space via the communications channel and means for receiving a decrypt key and a decrypt text/key relation. The encrypt text/key relation controls the encryption engine such that O
t
=&agr;
N
(t)+&pgr;
N
[&agr;
N−1
(t)+&pgr;
N−1
[&agr;
N−2
(t)+ . . . +&pgr;
2
[&agr;
1
(t)+&pgr;
1
[I
t
+&agr;
0
(t)]] . . . ]], mod W, where &agr;
N
, &agr;
N−1
, . . . , &agr;
1
, &agr;
0
are N+1 additive transformations defined by the encrypt key, where &pgr;
N
, &pgr;
N−1
, . . . , &pgr;
2
, &pgr;
0
are N permutations defined by the encrypt key, and where W represents the number of possibilities for each permutation defined by the encrypt key. The decrypt text/key relation controls the decryption engine such that I′
t
=&pgr;
1
−1
[&pgr;
2
−1
[&pgr;
3
−1
. . . [&pgr;
N−1
−1
[&pgr;
N
−1
[O
t
−&agr;′
N
(t)]−&agr;′
N−1
(t)]− . . . −&agr;′
3
(t)]−&agr;′
2
(t)]−&agr;′
1
(t)]−&agr;′
0
(t), mod W, where &pgr;
i
−1
is defined by the decrypt key as the inverse of the permutation &pgr;
i
, where &agr;′
N
, &agr;′
N−1
, . . . , &agr;′
1
, &agr;′
0
are N+1 additive transformations defined by the decrypt key, and where W represents the number of possibilities for each inverse permutation defined by the decrypt key.
According to one aspect of this embodiment, the encryption engine further includes W look-up tables for storing each of the possible W sets of permutations. According to a different aspect of this embodiment, the encryption engine further includes M<W look-up tables for storing M available sets of the possible W sets of permutations. According to a different aspect of this embodiment, the encryption engine further includes N<M<W look-up tables for storing N sets of permutations preselected from M available sets of the possible W sets of permutations. According to another aspect of this embodiment, &agr;(t) is a step function. According to a further aspect of this embodiment, &agr;
x
(t), X={0, 1, 2, . . . , N−1, N}, increments the sequence of &pgr;
x
for each value that t equals an integer multiple of R, where R is a prime number. According to a different aspect of this embodiment, &agr;
x
(t), X={0, 1, 2, . . . , N−1, N}, decrements the sequence of &pgr;
x
for each value that t equals an integer multiple of R, where R is a prime number. According to a different aspect of this embodiment, &agr;
x
(t), X={0, 1, 2, . . . N−1, N}, increments the s
Scheidt Edward M.
Wack C. Jay
Jack Todd
Peeso Thomas R.
Rabin & Champagne, P.C.
TECSEC Incorporated
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