Efficient method for encrypting superblocks of data

• US 5,008,935 A
• Filed: 06/30/1989
• Issued: 04/16/1991
• Est. Priority Date: 06/30/1989
• Status: Expired due to Term

• Current Assignee: American Telephone & Telegraph Company (AT&T, Inc.), Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: AT&T, Inc.
• Inventors: Roberts, Thomas J.
• Primary Examiner(s): Buczinski, Stephen C.
• Assistant Examiner(s): Gregory, Bernarr Earl
• Application Number:
  US07/374,314
• Time in Patent Office: 655 Days
• Field of Search: 380/9, 380/29, 380/36, 380/37, 380/42, 380/49, 380/50, 364/200, 364/900
• US Class Current: 380/29
• CPC Class Codes: H04L 2209/12 Details relating to cryptographic hardware or logic circuitry
• CPC Class Codes: H04L 2209/24 Key scheduling, i.e. generating round keys or sub-keys for block encryption
• CPC Class Codes: H04L 9/0625 with splitting of the data block into left and right halves, e.g. Feistel based algorithms, DES, FEAL, IDEA or KASUMI

Abstract

This invention relates to an arrangement for encrypting data for storage in a computer and/or for transmission to another data processing system. The plain text data is divided into buffers and the buffers are divided into blocks. The blocks are encrypted under the control of a first key using any block encryption method such as the Data Encryption Standard (DES). Individual bytes of the encrypted blocks of a buffer are then permuted under the control of a second key to form an encrypted buffer. Advantageously, the number of permutations for even a modest size buffer, say 256 bytes, is enormous, making unauthorized decryption using key searching methods computationally infeasible.

Claims

1. A method of encrypting superblocks of data comprising the steps of:

encrypting each of a plurality of blocks of each of said superblocks, using a first key, each encrypted block and each unencrypted block comprising a plurality of segments, each segment comprising a plurality of bits; and

permuting successive segments of said plurality of encrypted blocks over the range of each of said superblocks, using a second key, to form encrypted superblocks of data.

2. The method of claim 1 wherein said permuting comprises:

storing said successive segments of said plurality of blocks in locations of memory determined by successive elements of said second key.

3. The method of claim 2 wherein said segments are bytes.

4. The method of claim 2 wherein a processor having a word length n permutes said successive segments and wherein said segments are words of length n.

5. Apparatus for encrypting superblocks of data comprising:

means for encrypting each of a plurality of blocks of said superblocks of data, using a first key to form intermediate data, wherein each encrypted block and each unencrypted block comprises a plurality of segments, and each segment comprises a plurality of bits; and

means for permuting segments of said intermediate data over the range of each of said superblocks using a second key to form encrypted superblocks of data.

6. The apparatus of claim 5 wherein said means for permuting comprises a processor, operative under the control of a program for storing successive segments of said intermediate data in locations determined by successive elements of said second key.

7. The apparatus of claim 6 wherein said segments of said intermediate data are bytes.

8. The apparatus of claim 6 wherein said processor has a word length n and said segments of said intermediate data are words of length n.

9. A method of encrypting superblocks of data comprising the steps of:

encrypting a plurality of blocks of each of said superblocks, using a key, each encrypted block and each unencrypted block comprising a plurality of segments, each segment comprising a plurality of bits; and

permuting successive segments of said plurality of encrypted blocks over the range of each of said superblocks, using said key, to form encrypted superblocks of data.

10. The method of claim 9 wherein said permuting comprises:

storing said successive segments of said plurality of blocks in locations of memory determined by successive elements of said key.

11. The method of claim 10 wherein said segments are bytes.

12. The method of claim 10 wherein a processor having a word length n permutes said successive segments and wherein said segments are words of length n.

13. A method of encrypting a superblock of 4M bytes of plain text data comprising the steps of:

encrypting M 4-byte blocks of said superblock of plain text, using a first key, to form 4M bytes of intermediate data; and

permuting successive bytes of each byte of said intermediate data over the range of said superblock, using a second key, to form an encrypted superblock of data corresponding to said superblock of plain text data;

wherein said first and second key are formed from a password supplied by a user of said encryption method;

wherein said first key comprises a table of 256 3-byte words selected according to values of plain text and partially encoded bytes of a block; and

wherein said second key comprises 4M different address offsets for storage of successive bytes of said intermediate data to form said encrypted superblock of data.