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1. (WO2015173434) METHOD FOR PROVING RETRIEVABILITY OF INFORMATION
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C l a i m s

A method for proving retrievability, 'POR', of information, said method being performed in a memory available to one or more computation devices, wherein credentials between a user device, a storing device and an auditing device between each pair of said devices are exchanged and used for communication between them,

comprising the steps of

a) Encoding the information to be stored on said storing device by said user device or said auditing device,

b) Storing the encoded information on said storing device,

c) Verifying the correctness of said stored information by the auditing device using unpredictable random information,

d) Transmitting correctness information to the user device, said correctness information being secure and which are generated based on the result of said verification by the auditing device and

e) Validating said correctness information by the user device for proving retrievability of said stored information and said unpredictable random information.

The method according to claim 1 , wherein said auditing device is provided with contract information by the user device, said contract information specifying a checking policy for the auditing device and/or the information to be proved for retrievability.

The method according to claims 1 or 2, wherein said stored information is different from said information to be stored, wherein said information to be stored is recoverable from said stored information.

The method according to one of the claims 1 -3, wherein an information dispersal algorithm is applied to the information to be stored prior to storing.

5. The method according to one of the claims 1 -4, wherein a source for unpredictable random information is commonly used by the user device and the auditing device.

6. The method according to claim 5, wherein said source is based on Bitcoin.

7. The method according to one of the claims 1 -6, wherein said correctness information is based on information of an external mutually trusted entity.

8. The method according to one of the claims 1 -7, wherein said correctness information is provided in form of a log-file by the auditing device.

9. The method according to one of the claims 1 -8, wherein step c) and/or step e) is based on a proof-of retrievability protocol.

10. The method according to one of the claims 1 -9, wherein the auditing device performs a proof-of-retrieveabilty protocol with said storing device, and wherein the user device audits the auditing device using a proof-of- retrievability protocol.

1 1. The method according to claim 2, wherein said contract information includes at least one of the following: maximum interval within which the auditing device notifies the user device of an at least partial loss of said stored information, maximum failure tolerance.

12. A system for proving retrievability, 'POR', of information, said system comprising a user device, a storing device, and an auditing device, wherein credentials between said user device, said storing device and said auditing device between each pair of said devices are exchanged and used for communication between them,

Said user device or said auditing device being adapted to encode the information to be stored on said storing device, and said user device being adapted to validate correctness information for proving retrievability of said stored information using unpredictable random information,

Said storing device being adapted to store the encoded information,

Said auditing device being adapted to verify the correctness of said stored information using said unpredictable random information, and to transmit correctness information to the user device, said correctness information being secure and which are generated based on the result of said verification by the auditing device.

A method, performed by a user device, for proving retrievability, 'POR', of information

comprising the steps of

a1 ) exchanging credentials with a storing device and an auditing device to be used for communication between them,

b1 ) Preferably encoding the information to be stored on said storing device, c1) Initiating storing the encoded information on said storing device, d1 ) Receiving correctness information, wherein said correctness information being secure and which are generated based on the result of said verification and using unpredictable random information, and e1 ) Validating said correctness information and unpredictable random information for proving retrievability of said stored information.

A method, performed by an auditing device for proving retrievability, 'POR', of information,

comprising the steps of

a2) Exchanging credentials with a storing device and a user device to be used for communication between them,

b2) Verifying the correctness of stored information using unpredictable random information, and

c2) Transmitting correctness information to said user device, said correctness information being secure and which are generated based on the result of said verification.