STEP CODE CIPHERING SYSTEM

• US 3,798,360 A
• Filed: 06/30/1971
• Issued: 03/19/1974
• Est. Priority Date: 06/30/1971
• Status: Expired due to Term

• Current Assignee: Horst Feistel
• Original Assignee: Horst Feistel
• Inventors: Feistel, Horst
• Primary Examiner(s): Borchelt, Benjamin A.
• Assistant Examiner(s): Birmiel, H. A.
• Application Number:
  US05/158,174
• Time in Patent Office: 993 Days
• Field of Search: 178/22 331/78
• US Class Current: 380/37
• CPC Class Codes: H04L 9/0637 Modes of operation, e.g. cipher block chaining [CBC], electronic codebook [ECB] or Galois/counter mode [GCM]
• CPC Class Codes: H04L 9/065 Encryption by serially and continuously modifying data stream elements, e.g. stream cipher systems, RC4, SEAL or A5/3

Abstract

This specification discloses a system that provides multiple level encipherment of a block of data by means of a stepped block cipher process. A data stream consisting of digital information is segmented into blocks of dimension D, each block is enciphered by means of a block cipher cryptographic system operating under the control of a unique subscriber digital key. The cryptographic system develops a first cipher text of equal dimension as the block D. Then the cryptographic system is effectively shifted to accept a plurality of data bits from a second data block and a plurality of bits from the first cipher. The combination of block data bits and ciphertext data bits forms a composite block of dimension equal to the data block D. This combination is introduced to the cryptographic device for developing a second cipher text. The combined output of the second ciphertext and those information symbols from the first ciphertext which were not reintroduced to the cryptographic device are transmitted as a complete unit to a receiving station which will decipher the received multiple level cryptogram by an inverse process. The multiple level encipherment process is also utilized in a variant key embodiment which would encipher a data block D into a cipher C which is a function of a key control block consisting of a random combination binary digits that are continuously changing. In a further embodiment which utilizes multiple level encipherment, there is presented a method for providing secrecy in communications between a central processing unit and its data banks.

Claims

1. A process for multiple level encipherment of a data block consisting of binary digits said process comprising the steps of:

arranging a stream of binary digit data into a plurality of data segments;

loading one data segment from said plurality of data segments into a cryptographic block ciphering device for first generating a block cipher;

following the first generation of a block cipher, retaining a portion of said block cipher and combining it with another data segment to form a composite data block;

loading said composite data block into a cryptographic block ciphering device for generating a composite block cipher;

sequentially generating composite block ciphers from said data segments until said data stream is exhausted.

2. The process as defined in claim 1 wherein said cryptographic system develops a block cipher under the control of a combination of binary digits obtained from a unique key code associated with a particular individual.

3. The process as defined in claim 2 wherein said combination of binary digits comprises:

a block of binary digits whose combination at any particular time is a random arrangement of one'"'"''"'"'s and zero'"'"''"'"'s.

4. The process as defined in claim 3 wherein pairs of ciphers are generated under alternate control of a subscriber key and a random combination of binary digits.

5. The process as defined in claim 4 further comprising:

combining said random combination of binary digits with portions of data segments for generating composite ciphers.

6. A process for multiple level encipherment and decipherment of a stream binary data digits comprising the steps of:

segmenting said data stream into a plurality of blocks each n digits in dimension;

loading at least one of said blocks of n-digits into a cryptographic device for developing a first block cipher;

storing a portion of said first block cipher into a storage means;

loading further ones of said blocks of n-digits into said cryptographic device to be combined with the remaining portiOn of said first block cipher;

forming a second block cipher from the combination of a further block and said remaining portion of said first block cipher;

combining said first and second block ciphers into a composite block cipher in said storage means prior to transmission;

transmitting said composite block cipher;

receiving said composite block cipher at a receiving station and deciphering it by an inverse operation of said cryptographic device.

7. The system as defined in claim 6 wherein said block ciphers generated by said cryptographic device are alternately functions of a combination of binary digits associated with a particular subscriber to a computing network and a random combination of binary digit representations.