Data masking
Data masking is provided by, for at least one predetermined data item in data to be sent, applying a one-way function to that data item to produce a first value, producing a masked data item by encrypting the first value via a deterministic encryption scheme using a current encryption key for a current epoch, and replacing that data item by the masked data item. A data-provider computer sends the masked data to the data-user computer. On expiry of the current epoch, the data-provider computer generates a new encryption key for the encryption scheme in a new epoch, produces mask-update data, dependent on the current and new encryption keys, and sends the mask-update data to the data-user computer. The mask-update data permits updating, at the data-user computer, of masked data items produced with the current encryption key into masked data items produced with the new encryption key.
1. A computer-implemented method for data masking at a data-provider computer, the method comprising:
accessing, using a processor system, data to be sent to a data-user computer;
producing, using the processor system, masked data by, for at least one predetermined data item in the data to be sent, applying a one-way function to that data item to produce a first value, producing a masked data item by encrypting said first value via a deterministic encryption scheme using a current encryption key for a current epoch, and replacing that data item by the masked data item;
sending the masked data to the data-user computer; and
on expiry of said current epoch, generating a new encryption key for said encryption scheme in a new epoch, producing mask-update data, dependent on the current and new encryption keys, and sending the mask-update data to the data-user computer;
wherein said mask-update data permits updating, at the data-user computer, of masked data items produced with the current encryption key into masked data items produced with the new encryption key and said mask-update data comprises a predetermined function δ of the current and new encryption keys, and said encryption scheme comprises an algorithm Enc(k, X) for encrypting a value X under an encryption key k such that:
Enc (δ,( Enc ( s e ,X ))= Enc ( s e+1 ,X )
where s e is the current encryption key and s e+1 is the new encryption key and wherein said algorithm Enc(k, X)=X k and δ=s e+1 /s e .
2. The computer-implemented method as claimed in claim 1 including performing the steps of generating said new encryption key, producing said mask-update data, and sending the mask-update data to the data-user computer, on expiry of each of said new epoch and subsequent new epochs.
3. The computer-implemented method as claimed in claim 2 including, during each of at least some of said new epochs:
accessing further data to be sent to the data-user computer;
performing, for said further data, the step of producing masked data using the new encryption key as said current encryption key for that epoch, and sending the further masked data to the data-user computer.
4. The computer-implemented method as claimed in claim 1 wherein said encryption scheme comprises a symmetric encryption scheme and said mask-update data comprises the current encryption key and the new encryption key.
5. The computer-implemented method as claimed in claim 4 including applying said one-way function to said data item and a secret key of the data provider computer to produce said first value.
6. The computer-implemented method as claimed in claim 5 , wherein said one-way function comprises a hash function.
7. The computer-implemented method as claimed in claim 1 including applying said one-way function to said data item and a secret key of the data provider computer to produce said first value.
8. The computer-implemented method as claimed in claim 7 wherein said one-way function comprises a hash function.