Patent ID: 8290145
Filing Date: 2012-10-16
Classification: G06F,H04L

Abstract:
1. A method for transitioning from a first masked representation of a value to be kept secret to a second masked representation of the same value, wherein the value to be kept secret is prevented from being spied out, wherein the first masked representation is based on a first masking rule having a first mask and the second masked representation is based on a second masking rule having a second mask, the first masking rule being different from the second masking rule, and wherein, in transitioning from the first masked representation to the second masked representation, at least one previously calculated table having a plurality of entries is used and at least one calculation is carried out dependent on at least one randomly chosen veiling parameter, wherein the at least one randomly chosen veiling parameter is at least one parameter further to the first and second masks, and wherein the at least one randomly chosen veiling parameter influences the transitioning from the first masked representation to the second masked representation, thereby providing protection against an attack in which a plurality of calculation runs are statistically evaluated, wherein a table index of the table or of at least one of the tables, respectively, has a bit length that is smaller than the bit length of at least one of the first masked representation and the second masked representation, and wherein, in transitioning from the first masked representation to the second masked representation, repeated access takes place to the table or at least one of the tables, respectively, wherein operations of the method comprise: determining a third masked representation of the value to be kept secret, wherein the third masked representation is based on the first masking rule having a third mask; transforming the third masked representation into a fourth masked representation of the value to be kept secret using the table or at least one of the tables, respectively, wherein the fourth masked representation is based on the second masking rule having a fourth mask; and determining the second masked representation of the value to be kept secret from the fourth masked representation, wherein each operation of the method is executed by one or more processors on a smart card or chip module.