Processing information

1. A method for processing information, said method comprising:

dividing, by an apparatus, target information into N pieces of divided data using a secret sharing scheme in which a predetermined number (K) of pieces of the N pieces of divided data is required to restore the target information, wherein N>K, and wherein the apparatus is an information processing device that stores the N pieces of divided data;

said apparatus selecting M pieces from the N pieces, wherein K>0 and K<M<N;

after said selecting M pieces, said information processing device transmitting the selected M pieces to an external storage device that is external to the information processing device, said transmitting resulting in the M pieces being stored in the external storage device which limits a totality of pieces of the N pieces being stored on the external storage device to the M pieces;

after said transmitting the M pieces, restoring, in the information processing device, the target information from at least K pieces of the N pieces, and

after said restoring, destroying only D pieces of the M pieces in the external storage device, wherein D>M−K and D<M.

2. The method of claim 1 , wherein a remaining N−M pieces results from said selecting the M pieces from the N pieces, and wherein the method further comprises:

after said transmitting the selected M pieces and before said restoring the target information, storing L pieces of the remaining N−M pieces in the information processing device, wherein D≦M−K+L.

3. The method of claim 2 , wherein a remaining N−M−L pieces results from said storing L pieces, and wherein the method further comprises:

after said storing L pieces and before said restoring the target information, registering P pieces of the remaining N−M−L pieces with an external server, wherein D≦M−K+L+P; and

said information processing device receiving M′ pieces of the M pieces from the external storage device, wherein said restoring is performed by the information processing device and comprises utilizing the M′ pieces.

4. The method of claim 3 , wherein M′≧K, and wherein the at least K pieces consist of the M′ pieces.

5. The method of claim 3 , wherein M′<K, wherein the method further comprises said information processing device accessing the L pieces and the P pieces, and wherein the at least K pieces comprise the M′ pieces, the L pieces, and the P pieces.

6. The method of claim 1 , wherein said restoring is performed by the external storage device, wherein the at least K pieces consist of M′ pieces of the M pieces, wherein M′≧K, and wherein the method further comprises said external storage device transmitting the restored target information to the information processing device.

7. The method of claim 1 , wherein said destroying comprises:

randomly selecting at least one bit in each piece of the D pieces; and

after said randomly selecting at least one bit in each piece of the D pieces, inverting a value of each bit of the at least one bit in each piece of the D pieces.

8. The method of claim 7 , wherein said dividing the target information comprises using an encoding scheme that employs an error correcting code, and wherein the at least one bit in each piece of the D pieces consists of a number of bits that is larger than a correction limit of the error correcting code.

9. The method of claim 1 , wherein the method further comprises:

after said storing the M pieces and before said destroying D pieces, said external storage device ascertaining that a predetermined operation has been performed with respect to the external storage device and that a reference time has elapsed since the predetermined operation was performed, wherein said destroying in response to said ascertaining.

10. The method of claim 9 , wherein the predetermined operation is:

a removal of the external storage device from the information processing device, said removal having occurred after insertion of the external storage device into the information processing device; or

an operation of a switch comprised by the external storage device, wherein said operation of a switch has resulted in the external storage device receiving the reference time or a destruction rate according to which said destroying is to be performed.

11. The method of claim 9 , wherein the reference time is:

a function of a measured frequency at which the external storage device is connected to the information processing device;

a function of a shape or color of a cap placed on a connection terminal of the external storage device;

a function of a keyword used as a key in a search that retrieved a file comprising the keyword in the M pieces of divided data stored in the external storage device; or

a function of a type of a predetermined operation received by a switch comprised by the external storage device.

12. A system comprising a computer readable external storage device and an information processing device, said information processing device and said external storage device configured to perform a method for processing information, said method comprising:

an apparatus dividing target information into N pieces of divided data using a secret sharing scheme in which a predetermined number (K) of pieces of the N pieces of divided data is required to restore the target information, wherein N>K, and wherein the apparatus is an information processing device that stores the N pieces of divided data;

said apparatus selecting M pieces from the N pieces, wherein K>0 and K<M<N;

after said selecting M pieces, said information processing device transmitting the selected M pieces to an external storage device that is external to the information processing device, said transmitting resulting in the M pieces being stored in the external storage device which limits a totality of pieces of the N pieces being stored on the external storage device to the M pieces;

after said transmitting the M pieces, restoring, in the information processing device, the target information from at least K pieces of the N pieces, and

after said restoring, destroying only D pieces of the M pieces in the external storage device, wherein D>M−K and D<M.

13. The system of claim 12 , wherein a remaining N−M pieces results from said selecting the M pieces from the N pieces, and wherein the method further comprises:

after said transmitting the selected M pieces and before said restoring the target information, storing L pieces of the remaining N−M pieces in the information processing device, wherein D≦M−K+L.

14. The system of claim 12 , wherein said restoring is performed by the external storage device, wherein the at least K pieces consist of M′ pieces of the M pieces, wherein M≧K, and wherein the method further comprises said external storage device transmitting the restored target information to the information processing device.

15. The system of claim 12 , wherein said destroying comprises:

randomly selecting at least one bit in each piece of the D pieces; and

after said randomly selecting at least one bit in each piece of the D pieces, inverting a value of each bit of the at least one bit in each piece of the D pieces.

16. The system of claim 12 , wherein the method further comprises:

after said storing the M pieces and before said destroying D pieces, said external storage device ascertaining that a predetermined operation has been performed with respect to the external storage device and that a reference time has elapsed since the predetermined operation was performed, wherein said destroying in response to said ascertaining.

17. A computer program product, comprising a computer readable storage device having computer readable program code stored therein, said program code containing instructions executable, by a computer readable external storage device or by both the external storage device and an information processing device, to implement a method for processing information, said method comprising:

an apparatus dividing target information into N pieces of divided data using a secret sharing scheme in which a predetermined number (K) of pieces of the N pieces of divided data is required to restore the target information, wherein N>K, and wherein the apparatus is an information processing device that stores the N pieces of divided data;

said apparatus selecting M pieces from the N pieces, wherein K>0 and K<M<N;

after said selecting M pieces, said information processing device transmitting the selected M pieces to an external storage device that is external to the information processing device, said transmitting resulting in the M pieces being stored in the external storage device which limits a totality of pieces of the N pieces being stored on the external storage device to the M pieces;

after said transmitting the M pieces, restoring, in the information processing device, the target information from at least K pieces of the N pieces, and

after said restoring, destroying only D pieces of the M pieces in the external storage device, wherein D>M−K and D<M.

18. The computer program product of claim 17 , wherein the method further comprises:

after said storing the M pieces and before said destroying D pieces, said external storage device ascertaining that a predetermined operation has been performed with respect to the external storage device and that a reference time has elapsed since the predetermined operation was performed, wherein said destroying in response to said ascertaining.