US4782529A
Expired / Lapsed
US
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Decryption of messages employing unique control words and randomly chosen decryption keys
Assignee: Unisys Corp
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Filing: 1987-09-14
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Granted: 1988-11-01
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Expires: 2007-09-14
Abstract
Abstract In a communication network, a transmitting station sends encrypted messages to several receiving stations. Each receiving station stores one and the same set of decryption keys; and it stores a control word which is a series of bits that is unique to that station. Also, each receiving station identifies an encrypted message as being sent to it by -- (a) automatically selecting a decryption key at random from the set, (b) performing a decrypt operation on the same portion of the encrypted message from the transmitting station using the selected key, (c) comparing the result of the decrypt operation to its stored control word, and (d) repeating steps (a) thru (c) until either a match occurs or all keys in the set have been selected.
Inventors
- 👤 George T. Shima
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 09:57
CPC Classifications
H; H04; H04L; H04L9/00; H04L9/14; H04L9/32
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
166 words
For use in a communication network of the type in which a transmitting station sends an encrypted message to a plurality of receiving stations in a manner that enables only a selected receiving station in said plurality to decrypt the messages, a method of operation each receiving station, wherein: each of said receiving stations stores one and the same set of several decryption keys; each of said receiving stations stores a control word which is any series of bits that is unique to that station; and each of said receiving stations identifies an encrypted message as being sent to it by--(a) automatically choosing a decryption key at random from said set, (b) performing a decrypt operation on the same portion of the encrypted message from said transmitting station using the selected key, (c) comparing the result of said decrypt operation to its stored control word, and (d) repeating steps (a) thru (c) until either a match occurs or all keys in said set have been selected.
Claim 2
Dependent Claim
166 words
For use in a communication network of the type in which a transmitting station sends an encrypted message to a plurality of receiving stations in a manner that enables only a selected receiving station in said plurality to decrypt the messages, a method of operation each receiving station, wherein: each of said receiving stations stores one and the same set of several decryption keys; each of said receiving stations stores a control word which is any series of bits that is unique to that station; and each of said receiving stations identifies an encrypted message as being sent to it by--(a) automatically choosing a decryption key at random from said set, (b) performing a decrypt operation on the same portion of the encrypted message from said transmitting station using the selected key, (c) comparing the result of said decrypt operation to its stored control word, and (d) repeating steps (a) thru (c) until either a match occurs or all keys in said set have been selected.
Claim 3
Dependent Claim
52 words
A method according to claim 1 wherein the recited step (a) is performed by--storing a circular sequence of bits in a memory; randomly picking one bit in said sequence as the first bit of said decryption key; and reading successive bits of said stored sequence as successive bits of said decryption key.
Claim 4
Dependent Claim
29 words
A method according to claim 2 wherein to read successive bits of said decryption key, the number one is added to the memory address of the immediately preceding bit.
Claim 5
Dependent Claim
28 words
A method according to claim 2 wherein to read successive bits of said decryption key, the number one is subtracted from the address of the immediately preceding bit.
Claim 6
Dependent Claim
26 words
A method according to claim 1 wherein said portion of said encrypted message on which step (b) is performed is at the start of the message.
Claim 7
Dependent Claim
25 words
A method according to claim 1 wherein said portion of said encrypted message on which step (b) is performed is at a predetermined location therein.
Claim 8
Dependent Claim
27 words
A method according to claim 1 wherein said control word is of a type which has a secondary meaning independent of its use in generating said match.
Claim 9
Dependent Claim
159 words
For use in a communication network of the type in which a transmitting station sends an encrypted message to a plurality of receiving stations in a manner that enables only a selected receiving station in said plurality to decrypt the messages, a module for inclusion within each receiving station which comprises: one and the same set of several decryption keys; a control word which is any series of bits that is unique to each receiving station; and a control circuit including (a) a means for automatically choosing a decryption key at random from said set, (b) a means for performing a decrypt operation on the same portion of the encrypted message from said transmitting station using the selected key, (c) a means for comparing the result of said decrypt operation to the stored control word, and (d) a means for reactivating means (a) thru (c) until either a match occurs or all keys in said set have been selected.
Claim 10
Dependent Claim
159 words
For use in a communication network of the type in which a transmitting station sends an encrypted message to a plurality of receiving stations in a manner that enables only a selected receiving station in said plurality to decrypt the messages, a module for inclusion within each receiving station which comprises: one and the same set of several decryption keys; a control word which is any series of bits that is unique to each receiving station; and a control circuit including (a) a means for automatically choosing a decryption key at random from said set, (b) a means for performing a decrypt operation on the same portion of the encrypted message from said transmitting station using the selected key, (c) a means for comparing the result of said decrypt operation to the stored control word, and (d) a means for reactivating means (a) thru (c) until either a match occurs or all keys in said set have been selected.
Claim 11
Dependent Claim
58 words
A module according to claim 8 wherein said set of decryption keys is stored as a circular sequence of bits in a memory; and wherein said means for selecting randomly picks one bit in said sequence as the first bit of said decryption key and reads successive bits of said sequence as successive bits of said decryption key.
Claim 12
Dependent Claim
34 words
A module according to claim 9 wherein said means for selecting read consecutive bits of said decryption key from said memory by adding the number one to the address of the immediately preceding bit.
Claim 13
Dependent Claim
34 words
A module according to claim 9 wherein said means for selecting reads consecutive bits of said decryption key from said memory by subtracting the number one from the address of the immediately preceding bit.
Claim 14
Dependent Claim
21 words
A module according to claim 8 wherein said same portion of said encrypted message is at the start of the message.
Claim 15
Dependent Claim
20 words
A module according to claim 8 wherein said same portion of said encrypted message is at a predetermined location therein.
Claim 16
Dependent Claim
27 words
A module according to claim 8 wherein said control word is of a type which has a secondary meaning independent of its use in generating said match.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1991-11-01 | 1992-05-02 | 1992-11-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-11-01 | 1996-05-02 | 1996-11-01 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-11-01 | 2000-05-02 | 2000-11-01 | $7700.00 | Window Closed / Lapsed |