Cryptography – Communication system using cryptography – Data stream/substitution enciphering
Reexamination Certificate
1998-06-05
2001-11-27
Gregory, Bernarr E. (Department: 3662)
Cryptography
Communication system using cryptography
Data stream/substitution enciphering
C380S262000, C380S277000, C380S278000, C380S042000, C380S044000, C380S046000, C380S028000
Reexamination Certificate
active
06324287
ABSTRACT:
FIELD OF INVENTION
This invention relates generally to encryption methods and software, and more particularly to stream ciphers and one time pad encryption methods and software.
BACKGROUND OF THE INVENTION
One time pad encryption methods are well known. The first such method was invented in 1917 by Major Joseph Mauborgne and AT&T's Gilbert Vernam. Classically, a one time pad is a key of random letters, written on sheets of paper bound together in a pad. The pad is used to encrypt plain text and to decrypt the encrypted ciphertext. The pad is kept secret, and can be referred to as a private key. For security, the pad has the same or more letters than the message being encrypted. Accordingly, the pad is cumbersome, because it requires a large number of letters.
A one time pad provides perfect encryption, provided the letters of the pad are truly random. However, the burden of using a pad which is the same or a greater size than the text being encrypted makes one time pad methods generally non-applicable to consumer uses.
Encryption becomes less than perfect, if the key is less than perfectly random.
It would be beneficial to have a one time pad method which employs less random letters than the size of the message being encrypted.
It would be beneficial to enhance the security of one time pad methods which rely upon less than perfectly random, i.e., pseudo random, pads.
SUMMARY OF THE INVENTION
According to the present invention, characters for a pad are generated by selecting a seed file, extracting a first value from the seed file, generating a random number, and logically combining the first value with the random number to generate a first random character of the pad. To generate a next random character of the pad, a next value is extracted from the selected seed file, a next random number is generated, and the next random number is combined logically with the next value from the selected seed file to generate a next random character of the pad. This process repeats itself until a desired number of pad characters have been developed.
According to an embodiment of the present invention, logical combination by exclusive OR, i.e., XOR, is performed to generate a first random character. According to an embodiment of the present invention, a pad is produced having on the order of approximately 20,000 random characters.
According to the present invention, a user selects plain text to be encrypted and XORs the plain text with a pad at determined offset, to produce output cipher text. If the plain text is larger in number of characters than the pad, the pad is reused at a redetermined offset for XORing the not yet enciphered portions of the plain text. According to one embodiment of the present invention, the offset is a function of a user selected password. According to one embodiment of the present invention. The pad includes the user selected password or a derivative thereof.
According to the present invention, a pad is created with a software program stored on a selected memory medium a which space is reserved for storage of the pad created. Once the pad is created, it is stored at the reserved space. According to one embodiment of the present invention, the pad is additionally stored at another location for security. According to one embodiment of the present invention, the pad is stored on a flash card. According to one embodiment of the present invention, the software program is stored on a floppy disk. According to one embodiment of the present invention, the pad is stored at a reserved space on the floppy disk. According to one embodiment of the present invention, the software program is installed on a hard disk. According to one embodiment of the present invention, the pad is created by the software program with a seed file located on a hard disk drive, i.e., a hard drive.
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Gregory Bernarr E.
Schipper John
SCM Microsystems, Inc.
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