US5297208A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Secure file transfer system and method
Assignee: Individual
•
Filing: 1992-08-05
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Granted: 1994-03-22
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Expires: 2012-08-05
Abstract
Abstract This invention is a system and method for securely and robustly transferring a file from one computer to another without having a prearranged encryption key. Data is transferred by first generating some random numbers on each computer and undertaking some cryptographically secure handshaking in which a session key is determined. Then the file is broken up into blocks and encrypted with a chaining block cipher and transmitted. The blocks have headers which identify the them, and allow for detection and correction of transmission errors. Before retransmitting a block, an initialization vector is sent to synchronize the cipher modules. The random numbers are generated with keystroke timings combined with a pseudorandom number generator to expand the supply.
Inventors
- 👤 Roger Schlafly
- 👤 Michael J. Markowitz
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 07:25
CPC Classifications
H; H04; H04L; H04L9/00; H04L9/06; H04L9/0618; H04L9/0637; H04L9/08; H04L9/0816; H04L9/0838; H04L9/0841; H04L9/32; H04L9/3247; H04L9/3252
Claims Analysis
Total Claims: 22
Claim 1
Independent Claim
161 words
A file transfer system consisting of a plurality of computers connected by a communications channel, means for generating or retrieving random numbers in each of said computers, means for digital handshaking between said computers to establish communications, means for sending frames and data blocks through said channel, reliably and efficiently, means for transmitting an encryption initialization vector frame in order to synchronize cipher feedback, means for deriving a secure session key in each of said computers, based on said random numbers and on exchanged derived numbers, means for encrypting data blocks using said cipher feedback, means for detecting transmission errors, means for resending variants of said encryption initialization vector frame and said frames and data blocks in case of said transmission errors, means for sending an encrypted copy of a file or files based on said session key, means for receiving said encrypted copy of said file or files, and means for decrypting said received copy of said file or files.
Claim 2
Dependent Claim
161 words
A file transfer system consisting of a plurality of computers connected by a communications channel, means for generating or retrieving random numbers in each of said computers, means for digital handshaking between said computers to establish communications, means for sending frames and data blocks through said channel, reliably and efficiently, means for transmitting an encryption initialization vector frame in order to synchronize cipher feedback, means for deriving a secure session key in each of said computers, based on said random numbers and on exchanged derived numbers, means for encrypting data blocks using said cipher feedback, means for detecting transmission errors, means for resending variants of said encryption initialization vector frame and said frames and data blocks in case of said transmission errors, means for sending an encrypted copy of a file or files based on said session key, means for receiving said encrypted copy of said file or files, and means for decrypting said received copy of said file or files.
Claim 3
Dependent Claim
18 words
The system of claim 1 further comprising means to record keystroke time intervals to generate said random numbers.
Claim 4
Dependent Claim
29 words
The system of claim 1 further comprising means to generate said random numbers in advance, precompute modular exponentials of said random numbers, and save both in a storage device.
Claim 5
Dependent Claim
22 words
The system of claim 1 further comprising means to update said random numbers based on a pseudorandom number generator and timing information.
Claim 6
Dependent Claim
18 words
The system of claim 1 wherein said encryption initialization vector frame is based on the time of day.
Claim 7
Dependent Claim
23 words
The system of claim 1 further comprising means to verify the key exchange by transmitting an otherwise unused portion of said session key.
Claim 8
Dependent Claim
26 words
The system of claim 1 further comprising means to generate and validate a digital signature for the purpose of authenticating one or more of said computers.
Claim 9
Dependent Claim
20 words
The system of claim 1 further comprising means to revert to a non-secure standard file transfer protocol under certain circumstances.
Claim 10
Dependent Claim
26 words
The system of claim 1 further comprising means to calculate and transmit secure hash functions in order to verify the integrity of frames or data blocks.
Claim 11
Dependent Claim
51 words
The system of claim 1 wherein said means for a deriving a secure session key involves each of said computers sending a modular exponential of said random number, where said modular exponentials conform to the Digital Signature Algorithm (DSA) and said encryption and decryption conforms to the Data Encryption Standard (DES).
Claim 12
Dependent Claim
138 words
A file transfer method consisting of connecting a plurality of computers by a communications channel, generating or retrieving random numbers in each said computer, digital handshaking between said computers to establish communications, sending frames and data blocks through said channel, reliably and efficiently, transmitting an encryption initialization vector frame in order to synchronize cipher feedback, deriving a secure session key in each of said computers, based on said random numbers and on exchanged derived numbers, encrypting data blocks using said cipher feedback, detecting transmission errors, resending variants of said encryption initialization vector frame and said frames and data blocks in case of said transmission errors, sending an encrypted copy of a file or files based on said session key, receiving said encrypted copy of said file or files, and decrypting said received copy of said file or files.
Claim 13
Dependent Claim
138 words
A file transfer method consisting of connecting a plurality of computers by a communications channel, generating or retrieving random numbers in each said computer, digital handshaking between said computers to establish communications, sending frames and data blocks through said channel, reliably and efficiently, transmitting an encryption initialization vector frame in order to synchronize cipher feedback, deriving a secure session key in each of said computers, based on said random numbers and on exchanged derived numbers, encrypting data blocks using said cipher feedback, detecting transmission errors, resending variants of said encryption initialization vector frame and said frames and data blocks in case of said transmission errors, sending an encrypted copy of a file or files based on said session key, receiving said encrypted copy of said file or files, and decrypting said received copy of said file or files.
Claim 14
Dependent Claim
16 words
The method of claim 11 further comprising recording keystroke time intervals to generate said random numbers.
Claim 15
Dependent Claim
27 words
The method of claim 11 further comprising generating said random numbers in advance, precomputing modular exponentials of said random numbers, and saving both in a storage device.
Claim 16
Dependent Claim
20 words
The system of claim 11 further comprising updating said random numbers based on a pseudorandom number generator and timing information.
Claim 17
Dependent Claim
18 words
The method of claim 11 further comprising basing said encryption initialization vector frame on the time of day.
Claim 18
Dependent Claim
21 words
The method of claim 11 further comprising verifying the key exchange by transmitting an otherwise unused portion of said session key.
Claim 19
Dependent Claim
24 words
The method of claim 11 further comprising generating and validate a digital signature for the purpose of authenticating one or more of said computers.
Claim 20
Dependent Claim
18 words
The method of claim 11 further comprising reverting to a non-secure standard file transfer protocol under certain circumstances.
Claim 21
Dependent Claim
22 words
The method of claim 11 further comprising verifying the integrity of frames or data blocks by calculating and transmitting secure hash functions.
Claim 22
Dependent Claim
51 words
The method of claim 11 wherein said method for a deriving a secure session key involves each of said computers sending a modular exponential of said random number, where said modular exponentials conform to the Digital Signature Algorithm (DSA) and said encryption and decryption conforms to the Data Encryption Standard (DES).
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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) | 1997-03-21 | 1997-09-20 | 1998-03-22 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2001-03-21 | 2001-09-20 | 2002-03-22 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2005-03-21 | 2005-09-20 | 2006-03-22 | $7700.00 | Window Closed / Lapsed |