Method for ciphering data with error correction code

1. method for coding digital data (DATA) for transmission over a data transmission system represented by source symbols (Si) with an error-correction code for generating parity symbols (Pj) based on, for each parity symbol, a plurality of source symbols and at least one parity symbol having a rank that precedes a rank of a parity symbol being generated, the method comprising:

submitting part (mk) of the source symbols to at least a first ciphering; and

submitting the obtained ciphered symbols and the rest of the unciphered source symbols to the error-correction code.

2. The method of claim 1 , wherein the part (mk) of the source symbols (S i ) is submitted to a second ciphering for transmission with no coding, in addition to the parity symbols.

3. A method of claim 2 further comprising:

deciphering the symbols submitted to the second ciphering and received with no coding;

submitting the deciphered symbols to the first ciphering; and

submitting the symbols resulting from the previous step and the received parity symbols (P j ) to a decoding by the error-correction code.

4. The method of claim 2 , wherein the first and second cipherings differ by the used key and/or by the ciphering algorithm.

5. The method of claim 1 , wherein the number (mk) of ciphered source symbols ranges between 0.1% and 1% of the total number (k) of source symbols (S i ).

6. The method of claim 1 , wherein the source symbols (S i ) to be ciphered are selected so that each parity symbol (P j ) comprises at least one ciphered source symbol.

7. The method of claim 1 , wherein the error-correction code is represented by a parity matrix in which each line represents an equation for obtaining a parity symbol (P j ) and each column represents a source symbol (S i ) or a parity symbol, each parity symbol being obtained by a combination of the source and parity symbols identified in the columns of the corresponding line.

8. The method of claim 7 , wherein the source symbols (S i ) identified in less than 1% of the lines of the matrix based on the first one are submitted to the ciphering.

9. The method of claim 7 , wherein the part of the parity symbols (P j ) of the matrix forms a staircase.

10. The method of claim 7 , wherein the part of the parity symbols (P j ) of the matrix forms a triangle.

11. A digital data transmitter in an error-correction code transmission system, the transmitter comprising:

a circuit configured to code digital data (DATA) represented by source symbols (S i ) with an error-correction code for generating parity symbols (Pp based on, for each parity symbol, a plurality of source symbols and at least one parity symbol having a rank that precedes a rank of a parity symbol being generated,

wherein the circuit submits part (mk) of the source symbols to at least a first ciphering and submits the obtained ciphered symbols and the rest of the unciphered source symbols to the error-correction code.

12. The transmitter of claim 11 , wherein the part (mk) of the source symbols (S i ) is submitted to a second ciphering for transmission with no coding, in addition to the parity symbols.

13. The transmitter of claim 12 , wherein the circuit is further configured to:

decipher the symbols submitted to the second ciphering and received with no coding;

submit the deciphered symbols to the first ciphering; and

submit the symbols resulting from the previous step and the received parity symbols (P j ) to a decoding by the error-correction code.

14. The transmitter of claim 12 , wherein the first and second cipherings differ by the used key and/or by the ciphering algorithm.

15. The transmitter of 11 , wherein the number (mk) of ciphered source symbols ranges between 0.1% and 1% of the total number (k) of source symbols (S i ).

16. The transmitter of claim 11 , wherein the source symbols (S i ) to be ciphered are selected so that each parity symbol (P j ) comprises at least one ciphered source symbol.

17. The transmitter of claim 11 , wherein the error-correction code is represented by a parity matrix in which each line represents an equation for obtaining a parity symbol (P j ) and each column represents a source symbol (S i ) or a parity symbol, each parity symbol being obtained by a combination of the source and parity symbols identified in the columns of the corresponding line.

18. The transmitter of claim 17 , wherein the source symbols (S i ) identified in less than 1% of the lines of the matrix based on the first one are submitted to the ciphering.

19. The transmitter of claim 17 , wherein the part of the parity symbols (P j ) of the matrix forms a staircase.

20. The transmitter of claim 17 , wherein the part of the parity symbols (P j ) of the matrix forms a triangle.

21. A system for transmitting digital data by application of an error-correction code, the system comprising:

an encoding circuit to code digital data (DATA) represented by source symbols (S i ) with an error-correction code for generating parity symbols (P j ) based on, for each parity symbol, a plurality of source symbols and at least one parity symbol having a rank that precedes a rank of a parity symbol being generated,

wherein the encoding circuit submits part (mk) of the source symbols to at least a first ciphering and submits the obtained ciphered symbols and the rest of the unciphered source symbols to the error-correction code.

22. The system of claim 21 , wherein the part (mk) of the source symbols (S i ) is submitted to a second ciphering for transmission with no coding, in addition to the parity symbols.

23. The system of claim 22 , wherein the encoding circuit is further configured to:

decipher the symbols submitted to the second ciphering and received with no coding;

submit the deciphered symbols to the first ciphering; and

submit the symbols resulting from the previous step and the received parity symbols (P j ) to a decoding by the error-correction code.

24. The system of claim 22 , wherein the first and second cipherings differ by the used key and/or by the ciphering algorithm.

25. The system of 21 , wherein the number (mk) of ciphered source symbols ranges between 0.1% and 1% of the total number (k) of source symbols (S i ).

26. The system of claim 21 , wherein the source symbols (S i ) to be ciphered are selected so that each parity symbol (P j )comprises at least one ciphered source symbol.

27. The system of claim 21 , wherein the error-correction code is represented by a parity matrix in which each line represents an equation for obtaining a parity symbol (P j ) and each column represents a source symbol (S i ) or a parity symbol, each parity symbol being obtained by a combination of the source and parity symbols identified in the columns of the corresponding line.

28. The system of claim 27 , wherein the source symbols (S i ) identified in less than 1% of the lines of the matrix based on the first one are submitted to the ciphering.

29. The system of claim 27 , wherein the part of the parity symbols (P j ) of the matrix forms a staircase.

30. The system of claim 27 , wherein the part of the parity symbols (P j ) of the matrix forms a triangle.