Method for making safe an electronic cryptography assembly with a secret key

• US 8,582,774 B2
• Filed: 03/04/2003
• Issued: 11/12/2013
• Est. Priority Date: 03/07/2002
• Status: Expired due to Fees

• Current Assignee: Gemalto SA (Thales SA)
• Original Assignee: Gemalto SA (Thales SA)
• Inventors: Goubin, Louis, Akkar, Mehdi-Laurent
• Primary Examiner(s): Yalew, Fikremariam A
• Application Number:
  US10/506,851
• Publication Number:
  US 20100272264A1
• Time in Patent Office: 3,906 Days
• Field of Search: 726/34, 713/189, 380/277
• US Class Current: 380/277
• CPC Class Codes: H04L 2209/046 of operations, operands or results of the operations
• CPC Class Codes: H04L 9/003 for power analysis, e.g. differential power analysis [DPA] or simple power analysis [SPA]
• 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

An aim of this invention is to eliminate the risks of aggression “DPA of the n order” attacks, for all n values, of cryptography electronic assemblies or systems with a secret or private key. The process according to this invention concerns a securing process for an electronic system using a cryptographic calculation procedure using a secret key. The process consists of masking intermediate results in input or output of at least one critical function for the said procedure.

Claims

1. A method for operating an electronic system to secure a multi-round cryptographic calculation procedure wherein each round is performed using a round-operation that uses a secret key and an encryption function f or a replacement thereof, the method comprising operating the electronic system to:

determine a sequence of round-operations selected from a set of round-operations including round-operations performing a function p selected from the set of functions f, a masking operation followed by f, and f followed by an unmasking operation, and defined by whether each input of the round-operation has an input-type of masked or unmasked, respectively, and at least one output having an output-type of masked or unmasked depending on the input-types for the inputs, respectively, and the function p;

wherein the sequence of round-operations is selected such that for two sequential rounds i and i+1, each output from round i serves as an input to round i+1 and the output-type for each output from round i matches the input-type for the corresponding input to round i+1; and

execute the determined sequence of rounds.

2. The method of operating an electronic system to secure a multi-round cryptographic calculation procedure of claim 1 wherein the round-operations have a left input, a right input, a left output and a right output and are selected from the set including round-operations that:

A. accept unmasked inputs and produce unmasked output using the function f to produce the left output;

B. accepts unmasked inputs and produces an unmasked left output and a masked right output;

C. accepts an umasked left input, a masked right input and produces a masked left output, and an unmasked right output;

D. accepts a masked left input, an unmasked right input, and produces an unmasked left output, and a masked right output;

E. accepts a masked left input, an unmasked right input, and produces unmasked outputs.

3. The method for operating an electronic system to secure a multi-round cryptographic calculation procedure of claim 1 or 2 wherein at least one masking operation is a non-public masking operation.

4. The method for operating an electronic system to secure a multi-round cryptographic calculation procedure of claim 1 or 2 wherein the sequence of round-operations comprises a first and a second subsequence such and wherein the mask applied in the masking operations in the first subsequence is different from the mask applied in the second subsequence.

5. The method for operating an electronic system to secure a multi-round cryptographic calculation procedure of claim 4 wherein the end of the first subsequence is defined by a round-operation having all unmasked outputs.

6. An electronic system comprising:

storage device storing a cryptographic calculation procedure that uses a secret key executable by a processor,

a processor programmed to;

determine a sequence of round-operations selected from a set of round-operations including round-operations performing a function p selected from the set of functions f, a masking operation followed by f, and f followed by an unmasking operation, and defined by whether each input of the round-operation has an input-type of masked or unmasked, respectively, and at least one output having an output-type of masked or unmasked depending on the input-types for the inputs, respectively, and the function p;

wherein the sequence of round-operations is selected such that for two sequential rounds i and i+1, each output from round i serves as an input to round i+1 and the output-type for each output from round i matches the input-type for the corresponding input to round i+1; and

execute the determined sequence of rounds.

7. The electronic system of claim 6 wherein the round-operations have a left input, a right input, a left output and a right output and are selected from the set including round-operations that:

A. accept unmasked inputs and produce unmasked output using the function f to produce the left output;

B. accepts unmasked inputs and produces an unmasked left output and a masked right output;

C. accepts an umasked left input, a masked right input and produces a masked left output, and an unmasked right output;

D. accepts a masked left input, an unmasked right input, and produces an unmasked left output, and a masked right output;

E. accepts a masked left input, an unmasked right input, and produces unmasked outputs.

8. The electronic system of claim 6 or 7 wherein at least one masking operation is a non-public masking operation.

9. The electronic system of claim 6 or 7 wherein the sequence of round-operations comprises a first and a second subsequence such and wherein the mask applied in the masking operations in the first subsequence is different from the mask applied in the second subsequence.

10. The electronic system of claim 9 wherein the end of the first subsequence is defined by a round-operation having all unmasked outputs.

11. A non-transitory computer storage media operable to store instructions for instructing a processor of an electronic system to perform certain operations, the storage media comprising:

instructions to direct the processor to;

determine a sequence of round-operations selected from a set of round-operations including round-operations performing a function p selected from the set of functions f, a masking operation followed by f, and f followed by an unmasking operation, and defined by whether each input of the round-operation has an input-type of masked or unmasked, respectively, and at least one output having an output-type of masked or unmasked depending on the input-types for the inputs, respectively, and the function p;

wherein the sequence of round-operations is selected such that for two sequential rounds i and i+1, each output from round i serves as an input to round i+1 and the output-type for each output from round i matches the input-type for the corresponding input to round i+1; and

execute the determined sequence of rounds.

12. The non-transitory computer storage media of claim 11 wherein the round-operations have a left input, a right input, a left output and a right output and are selected from the set including round-operations that:

A. accept unmasked inputs and produce unmasked output using the function f to produce the left output;

B. accepts unmasked inputs and produces an unmasked left output and a masked right output;

C. accepts an umasked left input, a masked right input and produces a masked left output, and an unmasked right output;

D. accepts a masked left input, an unmasked right input, and produces an unmasked left output, and a masked right output;

E. accepts a masked left input, an unmasked right input, and produces unmasked outputs.

13. The non-transitory computer storage media of claim 11 or 12 wherein at least one masking operation is a non-public masking operation.

14. The non-transitory computer storage media of claim 11 or 12 wherein the sequence of round-operations comprises a first and a second subsequence such and wherein the mask applied in the masking operations in the first subsequence is different from the mask applied in the second subsequence.

15. The non-transitory computer storage media of claim 14 wherein the end of the first subsequence is defined by a round-operation having all unmasked outputs.