Method for making secure the execution of an intermediate language software code in a portable device

1. A method for executing an application compiled in intermediate code, on a portable digital device having a processor and a memory that implement a virtual executing machine for interpreting the intermediate code and executing a first set of arithmetic and/or logical operations on data items, comprising:

storing, in the memory, a second set of operations comprising operations that respectively correspond to each of the arithmetic and/or logical operations in said first set, wherein each operation of the second set is related to its corresponding operation in the first set by a predetermined checksum function;

generating, by the processor, a checksum item for each of a plurality of data items, based on the predetermined checksum function, and storing the checksum items in memory;

during execution of the application in the executing machine implemented by the processor and memory, performing the following security procedure for an operation that is carried out on data items:

a) providing, to the executing machine, at least one data item from said plurality of data items, and operations in said first set that are to be performed on the provided data item;

b) obtaining, by the executing machine, the stored checksum item corresponding to the data item provided to the executing machine, and operations in said second set that correspond to the operations provided in step (a);

c) performing, in parallel, by the executing machine, the operations provided in step (a) on the at least one data item provided in step (a), and the operations obtained in step (b) on the stored checksum item obtained in step (b); and

verifying the integrity of a security procedure at any time during the execution of operations by applying the predetermined checksum function to a result obtained at such time from execution of operations provided in step (a), and determining whether the checksum matches the result obtained at that same time from execution of operations provided in step (b).

2. The method of claim 1 , wherein the executing machine employs a first data structure stored in the memory for the data items and a second data structure stored in the memory for the checksum items.

3. The method of claim 2 , wherein the first and second data structures are respectively organized as first and second stacks in the memory.

4. The method of claim 2 , wherein the first and second data structures are respectively organized as first and second registers in the memory.

5. The method of claim 1 , wherein the executing machine employs a single data structure in the memory to store both the data items and the checksum items.

6. The method of claim 5 wherein the data structure is organized as a stack in the memory.

7. The method of claim 1 , wherein the verifying step is performed on a random basis.

8. The method of claim 1 , wherein the security procedure is performed in response to detection of a predetermined condition.

9. The method of claim 1 , wherein the security procedure is performed in response to interpretation of a predetermined portion of the intermediate code.

10. The method of claim 1 , wherein the security procedure is performed in a random manner.

11. A virtual machine for executing an application compiled in intermediate code on a portable digital device, wherein said virtual machine is stored in a non-volatile memory of the device and is configured to implement the method according to claim 1 .

12. A portable digital device comprising a non-volatile memory which stores the virtual machine according to claim 11 .

13. The device according to claim 12 , wherein said device is a chip card.