Hybrid stream cipher

• US 7,003,107 B2
• Filed: 05/22/2001
• Issued: 02/21/2006
• Est. Priority Date: 05/23/2000
• Status: Expired due to Fees

• Current Assignee: Mainstream Encryption
• Original Assignee: Mainstream Encryption
• Inventors: Ananth, Viswanath
• Primary Examiner(s): Barron, Gilberto
• Assistant Examiner(s): KIM, JUNG W
• Application Number:
  US09/864,042
• Publication Number:
  US 20020085710A1
• Time in Patent Office: 1,736 Days
• Field of Search: 380/37, 380/44, 380/46, 380/42, 380/43
• US Class Current: 380/37
• CPC Class Codes: H04L 2209/08 Randomization, e.g. dummy operations or using noise
• CPC Class Codes: H04L 2209/34 Encoding or coding, e.g. Huffman coding or error correction
• CPC Class Codes: H04L 2209/603 Digital right managament [DRM]
• CPC Class Codes: H04L 2209/605 Copy protection
• 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

In one embodiment, a hybrid stream cipher operating within a computing device. The hybrid stream cipher comprises at least two software routines. A first routine is responsible for dividing incoming plain text into variable-sized blocks. A second software routine is for converting the plain text into cipher text based on an encryption key, an internal identifier and perhaps a percentage of random data value.

Claims

1. A hybrid stream cipher operating within a computing device for encrypting data, comprising:

a first software routine to divide incoming plain text into variable-sized blocks based on information internally computed within the cipher, each block varying in size from a previous block in response to variations of an internal state of the computing device caused by changes in the incoming plain text; and

a second software routine to convert the blocks of plain text into cipher text.

2. The hybrid stream cipher of claim 1, wherein the first software routine operates internally within the hybrid stream cipher to produce the variable-sized blocks based on an encryption key, an internal identifier, an output of a first non-linear function and changes in the incoming plain text.

3. The hybrid cipher of claim 2, wherein each current block of the plain text is determined by (i) producing a pseudo-random sequence using a second non-linear function including the encryption key, the internal identifier and the output of the first non-linear function as inputs and (ii) accessing contents of the pseudo-random sequence as a number of data elements of the plain text forming the current block.

4. The hybrid cipher of claim 1, wherein the second software routine further performs a first shuffling operation on the internal state of a computing device based on an encryption key so that a single bit modification of the encryption key requires complete recalculation of the internal state of the computing device.

5. The hybrid cipher of claim 4, wherein the second software routine further performs a second shuffling operation on the internal state of the computing device based on at least an internal identifier to mitigate a likelihood of prediction of the internal state of the computing device upon knowledge of the encryption key.

6. The hybrid cipher of claim 1 further comprising:

a third software routine to automatically determine if a plurality of random data elements are to be distributed within the cipher text and to distribute the random data elements without user intervention.

7. The hybrid cipher of claim 6, wherein the third software routine determines an amount of random data elements distributed within the cipher text is programmable based on a percentage value entered by a user, or set based on an encryption key and an internal identifier and the internal state of the computing device.

8. The hybrid cipher of claim 6, wherein the third software routine determines an amount of random data elements distributed within the cipher text is set based on the encryption key, the internal identifier and the internal state of the computing device.

9. The hybrid cipher of claim 6, wherein the plurality of random data elements are produced by a pseudo-random generator.

10. The hybrid cipher of claim 1 further comprising a third software routine to map the input plain text before undergoing operations of the second software routine to avoid statistics of the plain text from reflecting on the internal state of the computing device.

11. The hybrid cipher of claim 1 further comprising a third software routine to produce an output stream based on a mixing of the cipher text, a plurality of random data elements and a hash digest of a portion of the output stream, a bit length of the output stream being varied based on variations of the internal state of the computing device.

12. The hybrid cipher of claim 1 further comprising a third software routine to distribute one of a digital signature and a watermark in the cipher text in order to detect modification.

13. The hybrid cipher of claim 12 further comprising a fourth software routine to calculate and distribute a hash of the cipher text, a plurality of the random data elements and the digital signature within an output stream.

14. The hybrid cipher of claim 1 further comprising a third software routine to convert cipher text to plain text based on a table lookup using an array having data elements that are permuted to correspond to an inverse of an array of the internal state of the computing device.

27. The hybrid cipher of claim 2, wherein each block of the plain text is segmented by (i) producing a pseudo-random sequence using a second non-linear function including the encryption key, the internal identifier and the output of the first non-linear function as inputs and (ii) accessing contents of the pseudo-random sequence to identify a number of data elements of the plain text forming the block.

28. The hybrid cipher of claim 1 further comprising:

a third software routine to automatically determine if a plurality of random data elements are to be distributed within the cipher text based on the internal state of the computing device.

15. A computing device comprising:

a memory to store code operating as a stream cipher; and

an electronic component coupled to the memory and adapted to segment input data into random sized blocks forming a sequence of blocks, the size of each block of the sequence of blocks varying in response to changes in the input data, the electronic component adapted to further perform a stream cipher operation on the random sized blocks.

16. The computing device of claim 15, wherein the stream cipher operation involves encryption using an encryption key to produce cipher text that varies in response to changes in the encryption key.

17. The computing device of claim 15, wherein the electronic component is an integrated circuit.

18. The computing device of claim 15, wherein a hybrid stream cipher processed by the electronic component produces random-sized blocks of the input data based on an encryption key, an unique internal identifier, an output of a first non-linear function and changes in the incoming plain text.

19. The computing device of claim 18, wherein each block of the plain text is determined by the hybrid stream cipher (i) producing a pseudo-random sequence using a second non-linear function including the encryption key, the internal identifier and the output of the first non-linear function as inputs and (ii) accessing contents of the pseudo-random sequence as a number of data elements of the plain text forming the current block.

20. The computing device of claim 15, wherein the computing device is one of a smart card and a node coupled to a network and alternatively a router.

21. The computing device of claim 15, wherein the electronic component to segment the random sized blocks into a plurality of blocks including at least three successive blocks varying in length based on variation of an internal state of the computing device caused by variations in the input data.

22. The computing device of claim 15, wherein the electronic component segments each of the random sized blocks into blocks each varying in length.

23. The computing device of claim 15, wherein the computing device is one of an operating system and a wireless device.

24. The computing device of claim 15, wherein the memory of the computing device is a portable storage medium that, only when in communication with the electronic component, enables the electronic component to perform the stream cipher operation on the random-sized blocks.

29. The computing device of claim 15, wherein a hybrid stream cipher processed by the electronic component internally produces random sized blocks of the input data in response to changes in an internal state of the computing device, the random sized blocks undergoing cryptographic operations to produce ciphertext.

25. A hybrid stream cipher operating within a computing device for encrypting data, comprising:

a first software routine to divide incoming plain text into variable-sized blocks with each block varying in size and a size of each variable-sized block changing based on changes of an internal state of the computing device caused by variations in the incoming plain text; and

a second software routine to convert the plain text into cipher text based on the encryption key and an internal identifier.

26. The hybrid stream cipher of claim 25, wherein the first software routine operating internally within the hybrid stream cipher produces the variable-sized blocks based on the encryption key, an internal identifier and an output of a first non-linear function.