A secure calculation is performed on at least one input value. The calculation includes a number of operations, with a first operation performed on the input value, and subsequent operations performed on results produced by previous operations. An initial encryption rank is set, based on the number of operations to be performed in the calculation. The input value is encoded, together with the initial encryption rank. The calculation is then performed, such that the first operation is performed on the encoded input value to produce an encoded result, and subsequent operations are performed on respective encoded results produced by previous operations to produce further encoded results. A new encryption rank is set when an operation in the calculation is performed on the encoded input value or on an encoded result produced by a previous operation, such that the encoded result of said operation in the calculation has the new encryption rank. A decoding function provides a useable output value from an encoded result only if the encoded result has an encryption rank that has reached a predefined value.