Method for storing data in a cloud and network for carrying out the method

1. A method for storing data in a cloud, the method comprising:

providing at least one data file to be stored together with a predefined number t of replicas of the at least one data file within the cloud, at least one authentication tag corresponding to the at least one data file and t functions that are configurable to take at least a predefined time to compute;

transmitting the at least one data file, the at least one authentication tag and the t functions to the cloud;

storing the at least one data file within the cloud;

computing t solutions of the t functions within the cloud;

generating the t replicas of the at least one data file based on the t solutions of the t functions and the at least one data file within the cloud, wherein each of the t functions is used for at least one of the t replicas of the at least one data file; and

storing the t replicas within the cloud.

2. The method according to claim 1 , wherein the t functions each are not parallelizable and/or comprise exponent E and/or comprise a one-way function.

3. The method according to claim 1 , wherein the t functions are time-lock puzzles.

4. The method according to claim 3 , wherein at least one or each of the puzzles is based on exponentiation modulo a composite number.

5. The method according to claim 3 , wherein at least one or each of the puzzles exhibits a trapdoor based on an Euler totient function.

6. The method according to claim 3 , wherein at least one or each of the puzzles is based on finding a pre-image of a one-way function.

7. The method according to claim 1 , wherein each of the t solutions is efficiently verifiable.

8. The method according to claim 1 , wherein a processed file comprising the at least one data file and the at least one authentication tag is provided and transmitted to the cloud.

9. The method according to claim 1 , wherein a challenge is issued for blocks contained across all of the t replicas.

10. The method according to claim 9 , wherein the cloud computes a response to the challenge under consideration of the at least one authentication tag and the at least one data file and the t replicas stored.

11. The method according to claim 10 , wherein the time it takes for the cloud to respond is measured.

12. The method according to claim 10 , wherein the response is verified under use of a trapdoor function to ensure that all replicas are stored.

13. The method according to claim 1 , wherein proof of integrity for at least one or all of the t replicas is performed by a challenge-response protocol and/or by use of a homomorphic nature of the at least one authentication tag.

14. A network for carrying out a method for storing data in a cloud, the network comprising:

a transmitter configured to transmit to the cloud: at least one data file to be stored together with a predefined number t of replicas of the at least one data file within the cloud, at least one authentication tag corresponding to the at least one data file and t functions that are configurable to take at least a predefined time to compute;

a storage configured to store the at least one data file within the cloud;

a computer configured to compute t solutions of the t functions within the cloud;

a generating computer configured to generate the t replicas of the at least one data file based on the t solutions of the t functions and the at least one data file within the cloud, wherein each of the t functions is used for at least one of the t replicas of the at least one data file; and

a storage configured to store the t replicas within the cloud.